What causes bitterpit

This article discusses causes of bitterpit. Frequently I see the result but seldom does anyone discuss prevention Bitter Pit - an overview | ScienceDirect Topics

" Bitter Pit

Bitter pit, the collapse of cell clusters usually after storage of the fruit, is generally prevented by sufficient calcium and accentuated by high magnesium.

From: Encyclopedia of Food Sciences and Nutrition (Second Edition), 2003

Related terms:

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Physiological Disorders and Their Control

Elhadi M. Yahia, … Adriana Sañudo, in Postharvest Technology of Perishable Horticultural Commodities, 2019

Bitter Pit

Bitter pit (Fig. 15.12) is a disorder affecting the appearance of apples. The disorder consists of circular depressions of dark skin color affecting the postharvest quality of fruit. The disorder has been related to a localized calcium deficiency during the stages of cell division and elongation occurring during a period of 4–6 weeks after anthesis. Mineral imbalance in this stage might produce a decrement in calcium levels and the consequent increment of potassium and magnesium concentration, thus affecting cell membrane permeability and progressive cell death. Bitter pit symptoms appear more frequently at the end of the fruit calyx and are seasonally associated with dry summers. The varietal sensibility is a main factor influencing the disorder; that is the cultivars Granny Smith, Gala, Golden Delicious, and Honeycrisp might present the symptoms even before harvest. Other closely related factors are excessive nitrogen nutrition, high salinity, poor pollination, light crop load, and elevated positions of fruit on the trees. Other disorders occurring in apples during storage are Jonathan spot, internal breakdown, and storage scalds."

" Bitter pit and cork spot


Bitter pit and cork spot

Physiological disorder

Distribution: Widespread


Small, green to purplish to light brown, slightly sunken lesions appear on mature fruit.

Small, green to purplish to light brown, slightly sunken lesions appear on mature fruit.William Turechek, USDA-ARS

  • Small, green to purplish to light brown, slightly sunken lesions appear on mature fruit.
  • Individual lesions are dry and do not extend deep into the fruit.

Small, green to purplish to light brown, slightly sunken lesions appear on the surface of mature fruit (A). Individual lesions on the fruit surface are dry and do not extend deep into the fruit (B); however, cutting into the fruit can reveal numerous internal lesions. Bitter pit usually develops in storage and is most severe at the calyx end. A similar calcium-related disorder that occurs only on d’Anjou pears is named cork spot.

  • Crops Affected: Apples, Pears


This is a physiological disorder associated with calcium deficiency in apple fruit. It is common on the varieties Cortland, Gravenstein, Honeycrisp, Northern Spy, and York. Losses can be minimized by avoiding excessive tree vigor (because shoots compete with fruit for calcium) and applying calcium sprays during summer.

Similar Species

On apple, symptoms can be confused with other calcium-related physiological disorders such as Jonathan spot and the disease Brooks fruit spot.


In addition to causing bitter pit, calcium deficiency also increases susceptibility to canker. I’ve found dramatic improvements from simply giving my trees crushed oyster shell.


I’ve had less issues with apple maggots after supplementing with calcium as well.


Crushed oyster shells? Interesting. How much do you put around each tree? Where do you get your crushed oyster shells? I see all sorts of different prices when I pull up bags of these. TY
I have had a few apples ( not the whole tree though) over the years that has had bitterpit. So having a chance to prevent it before you get it would be good.

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50lb bags of crushed oyster shells are cheap if you go to a feed store where they’re sold as a chicken dietary supplement. I apply unmeasured amounts rather indiscriminately since it isn’t all instantly available so isn’t a huge risk of over doing. There will be some portions which are more powdery and quickly available as well as the larger flakes which will be more slow release.

I’m in western Washington. It’s the rainy side of the state so much of the calcium is leached away.


It looked like I could get bags of the crushed oyster shells at feed stores since it is used for chickens. I was not sure if this was where you bought yours. I am glad this helped you. I will get some to put around my trees. We get a lot of rain mostly in the spring. At times 2-5 inches at a time. It can’t hurt to add the crushed oyster shells.


In Kansas some grain farmers who need it apply tons of ag lime to their fields. Oyster shells are not as readily available here. Oyster shell is more expensive but better. Chicken egg shells are great when you need a small amount of calcium for a plant or two or just 1 tree. Normally egg shells are part of the compost pile. Calcium deficiency we know also causes blossom end rot in tomatoes. If this has been a problem start treating asap after petal fall Calcium sprays for bitter pit should start at petal fall | Good Fruit Grower
The trees will be done with uptake by July. This year adding it as a solid might be to late so you will want to use a calcium foliar spray. " Calcium sprays for bitter pit should start at petal fall

January 1, 2013

Apple growers in the eastern United States should start calcium sprays at petal fall and continue them through the season to reduce the incidence of bitter pit on susceptible varieties.

Dr. Steve Hoying, Cornell University pomologist in New York’s Hudson Valley, laid out his recommendations during fruit growers’ schools this spring.

Large-fruited cultivars—Fuji, Jonagold, Cortland, Red Delicious, Golden Delicious, and, especially, Honeycrisp—need repeated applications of calcium, which growers usually apply as calcium chloride. Most calcium is taken into the fruit by mid-July, he said, so sprays should begin soon after petal fall to be most effective.

Bitter pit-sensitive cultivars should be treated with three to four cover sprays containing one to two pounds of calcium chloride (78 percent calcium) or its equivalent per 100 gallons at 14-day intervals beginning seven to ten days after petal fall, he said.

Two additional sprays of three to four pounds per 100 gallons should be made four and two weeks prior to harvest.

This recipe provides 7.5-13.4 pounds of actual calcium per acre for an orchard that requires 300 gallons of dilute spray per acre, he said.

Bitter pit can be more prevalent when there is excess tree vigor, winter injury, large fruit, low crop load, excessive pruning, variable water availability and supply, and nutritional imbalances, he said. Nutritional imbalances include high nitrogen levels and low calcium to potassium and calcium to magnesium ratios.

Control of bitter pit on susceptible cultivars requires foliar application of calcium because calcium is relatively immobile in the tree and may be deficient in fruit even when it is found in adequate amounts in the soil or other tree parts, Hoying said.

Most calcium is taken into the fruit by mid-July. From then to harvest, calcium within the fruit is diluted as the fruit increases in size. Thus, sprays must begin after petal fall to be most effective, he said.

The source of the calcium is not as important as getting sufficient amount on the fruit and at the correct time.

If nitrogen levels are low, Hoying recommends using calcium nitrate for the first two sprays and then calcium chloride for the remaining sprays. In orchards well supplied with nitrogen, applications of calcium nitrate may result in poor-colored fruit that do not store well.

Calcium sprays must contact the fruit for uptake to be effective. Therefore, water volumes capable of wetting the entire tree are required.

Calcium products should be compatible with most wettable powders. Calcium chloride and calcium nitrate are not compatible with magnesium sulfate (Epsom salt), Polyram, certain wettable sulfur formulations, and may inactivate Apogee, he said.

If there is doubt concerning compatibility of calcium with pesticides in foliar sprays, consult the manufacturer of the pesticide or use other sources of calcium known to be compatible, Hoying advised.

@alan mentioned many times of problems with excess nitrogen in an orchard. He discussed composting with wood chips many years and questioning if excess nutrients might be building up. Many growers when first starting to grow apples apply excessive fertilizer higher in nitrogen to cause the trees to grow. That might sound ok but appmying nitrogen for growth going into winter is a bad idea the same as late spring. Nitrogen should be applied in Kansas in late March or early April but in every place the times will be different as trees start to wake up and grow. That is a big mistake to apply nitrogen at the wrong time because nitrogen is a problem with calcium uptake. Bitter Pit Control in Apples

" Bitter Pit Control in Apples

Factsheet - ISSN 1198-712X - Copyright Queen's Printer for Ontario
Agdex#: 211/690
Publication Date: 03/00
Order#: 00-009
Last Reviewed: 08/09
History: Replaces Factsheet “Bitter Pit Control in Apples” (Order No. 92-027
Written by: John Cline - University of Guelph

Table of Contents

  1. Introduction
  2. General Description
  3. Orchard Management
  4. Calcium Nutrition
  5. Fruit Analysis
  6. Timing of Calcium Sprays
  7. Caution
  8. Coverage
  9. Sources of Calcium
  10. Compatibility With Other Spray Materials
  11. Summary


Bitter pit is a physiological disorder of apple fruit that has caused serious losses in certain apple varieties for many years. Spy is frequently affected by this disorder. With the right conditions, bitter pit can occur on Delicious, Idared, Crispin, Cortland, Empire, Honeycrisp and other varieties. The bitter pit sensitivity of some of the newer cultivars is not accurately known at this time. Bitter pit may not be evident at harvest but develops in stored fruit and can result in extensive loss from storage.

General Description

Bitter pit is the physiological breakdown of cells under the skin, causing slight depressions generally concentrated at the calyx end of the fruit (Figure 1). The tissue in these depressed areas is darkened, dry and spongy with a bitter taste. In some instances the symptoms may not be apparent on the fruit surface but appear under the skin. Large fruit from trees with light crops are more likely to have bitter pit. Excessive nitrogen (N), potassium (K) or fluctuating soil moisture can cause bitter pit. Calcium (Ca) has an important role in cell wall development. When Ca is in short supply, cell wall integrity is lost, resulting in these symptoms which vary slightly between varieties.

Image of apple with a section cut to reveal many brown spots that extends from the skin into the flesh.

Figure 1. Typical bitter pit symptoms on fruit.

Orchard Management

Cultural practices in orchards with a history of bitter pit may be modified to minimize this disorder. Consider the following factors.

Nutritional Factors

  • Ca nutrition is directly involved in bitter pit development and is discussed later in this factsheet. Other nutrients interact with Ca within the fruit. Upset nutrient balances can result in more serious bitter pit problems.

For example, excessive N causes large fruit that results in a dilution of Ca in the fruit and more serious bitter pit. Apply N fertilizer on the basis of leaf analysis. Excessive N is also indicated by excessive growth and large dark leaves. If N levels are high, reduce the rate of N and in extreme cases, do not apply N fertilizer. Apply N fertilizer as early in spring as possible. Research has shown that applying N after the middle of April increases the incidence of bitter pit.

Excessive K fertilizer applications can also depress Ca in the fruit, particularly when Ca levels are low. Apply K fertilizer only when leaf analysis indicates a need.

Boron (B) is involved in movement of Ca to the fruit. If B is low, Ca disorders such as bitter pit may develop. Be sure there is an adequate B level in the leaves by leaf analysis.

  • Pruning can result in higher N levels. If trees are to be severely pruned, reduce the amount of N fertilizer. Moderate annual pruning is best.
  • Mulch will even-out soil moisture fluctuations, helping to avoid bitter pit. Do not use mulch materials high in N, such as legume hay. A wide herbicide band with the sod herbicide system of soil management may lead to excessive N and more serious bitter pit problems. The herbicide strip should not extend beyond the spread of the tree branches.
  • Excessive fruit thinning or light crops result in large fruit. Annual cropping should be promoted by proper thinning. Apply Ca sprays when the crop is light or the fruit is large.
  • Since the disorder develops in storage, loss can be reduced by immediately marketing large fruit or fruit from areas where bitter pit has been a problem.

Calcium Nutrition

Bitter pit is closely related to the Ca nutrition of the fruit. Ca is relatively immobile within trees. There can be ample Ca in the leaves and soil but a shortage within the fruit. For this reason, fruit Ca is a much better indicator of potential bitter pit problems than leaf or soil Ca. A gradient of Ca concentrations is found from the stem (high Ca) to the calyx (low Ca) end of the fruit where bitter pit shows first.

Most of the Ca is taken into the fruit by mid-July. From then to harvest, Ca within the fruit is diluted as the fruit increases in size. The larger the fruit the more the dilution, and the more likely there is to be a shortage of Ca. There may even be some export of Ca out of the fruit late in the season. Ca sprays applied to the fruit during this time of fruit enlargement have increased fruit Ca concentrations and reduced the incidence of bitter pit. Soil application of Ca, in contrast, has not been effective in reducing the incidence of bitter pit.

Fruit Analysis

Fruit analysis is a helpful indicator of the Ca level within the fruit and the potential risk of bitter pit development in storage. Select 20 average-sized fruit per sample 3 weeks before harvest. Wash samples with distilled water to remove surface Ca deposits. Opposite longitudinal sections, cut from stem cavity to calyx, excluding stems and seeds, are combined to give a sample of apple fruit to be analyzed. Typical optimum analytical values for different cultivars for long-term storage are given in Table 1.

Ca levels should be higher for long-term CA storage. At high Ca levels, K levels will be less detrimental than at low Ca levels, and in fact may improve fruit quality of certain cultivars. At low Ca levels, high K may depress Ca and result in more bitter pit. The ratio of K/Ca should not exceed 25:1.

Table 1. Optimum Apple Fruit Composition 3 Weeks Before Harvest (excluding seeds and stems)|Expressed in mg/100g of fresh weight|N mg/100g|K mg/100g|Ca mg/100g|Mg mg/100g|K/Ca Ratio less than:|
| — | — | — | — | — | — |
|McIntosh, Empire, Spy|30-50|70-100|4.0-5.0|4.0-5.0|25:1|
|Delicious, Crispin, Idared|40-60|100-120|4.5-5.5|4.5-5.5|25:1|

Timing of Calcium Sprays

Under Ontario conditions Ca sprays should be applied to the fruit beginning in early July and repeated at 2-week intervals. At least 4 sprays are needed. Where a greater amount of total calcium is required, additional applications can be made by beginning earlier (mid-June) or by continuing applications up until harvest if required. In general, the more Ca applied, the larger the fruit Ca concentrations and the better the bitter pit control. Ca sprays have been applied right up to harvest and even as a dip after harvest.


With red varieties, the deposit of Ca on the fruit surface resulting from repeated Ca sprays in dry weather, close to harvest, may result in depressed colour development.

The application of foliar sprays of Ca has also been shown to advance fruit maturity. When foliar Ca is being applied fruit maturity should be monitored beginning several days before anticipated harvest.


Calcium sprays must contact the fruit for uptake to be effective, therefore water volumes capable of wetting the entire tree are required. If concentrate spraying must be used - apply sprays at 10-day intervals until total amount of calcium is applied.

Sources of Calcium

Calcium chloride is perhaps the most economical source of Ca and has given effective control of bitter pit. It can however, cause foliar burning in some cultivars and conditions (Figure 2). Calcium chloride should not be applied at temperatures above 25°C nor under slow drying (high humidity) conditions. McIntosh, Golden Delicious and Idared foliage is very sensitive to calcium and should not be sprayed with calcium chloride.

Commercially calcium chloride is available in flake form (78% CaCl2). This contains 28% elemental Ca. Rates of calcium chloride are shown in Table 2. Do not exceed the concentration shown. Calcium nitrate is another source of Ca that has been used for bitter pit control. Commercial calcium nitrate contains 79% Ca (NO3)2, 19% elemental Ca and 13.5% N.

In orchards well supplied with N, applications of calcium nitrate may result in poor-coloured fruit that does not store well and for this reason should not be used. If N levels are lower, calcium nitrate might be used for the first 2 sprays in July and calcium chloride for the remaining sprays.

Image of apples and leaves damaged by calcium chloride.

Figure 2. Necrotic leaf margins can be caused by too high a concentration of calcium chloride or by applying calcium chloride at temperatures above 25°C.

Avoid spraying Crispin and Golden Delicious with calcium nitrate, since fruit damage may result. Rates of calcium nitrate are shown in Table 2. Other sources of Ca are available and have been found to control bitter pit provided sufficient Ca is applied.

There is debate as to whether these are more effective per unit of Ca than calcium chloride and calcium nitrate.

Apply at least 20% of the total calcium shown in Table 2. This would require a total of 50 L/ha of 6% Ca (This Ca, OligoCa), 37.5 L/ha of 8% Ca (Liqui-Cal), 30 L/ha of 10% Ca (CaB’y), 25 L/ha of 12% Ca (Stopit), and 17.5 L/ha of 24% CaO (Wuxal). These are total amounts spread over the growing season in 4-5 applications and are minimum amounts.

If conditions are right for bitter pit development, rates could be doubled. These materials can be applied in low volume but sufficient water must be applied to ensure thorough wetting of the fruit and foliage. Check with the manufacturer regarding compatibility with other spray materials. Ca sources should be compared on the basis of cost per unit of Ca.

Be sure to wash the sprayer thoroughly after spraying, since Ca salts are corrosive.

Table 2. Rates of Calcium Chloride and Calcium Nitrate for Bitter Pit Control|Time|Calcium kg/ha|Calcium chloride kg/ha/2000L*|Calcium nitrate** kg/ha/2000L*|
| — | — | — | — |
|End July|3.5|12|18|
|End Aug|4|14|21|

  • If lower volumes/ha are used, spray more frequently so that the total amount of Ca is applied during the season. Do not concentrate Ca sprays.

** Calcium nitrate should not be used in August unless the orchard is deficient in nitrogen.

Compatibility With Other Spray Materials

Calcium chloride or calcium nitrate are compatible with most wettable powders including captan, Guthion and Imidan when sprayed dilute (2000 L/ha). Dissolve the calcium chloride in a pail and thoroughly mix in the spray tank before creaming the wettable powders and adding them. Be sure there is thorough agitation during application.

Sprays containing calcium chloride or calcium nitrate are known to be incompatible with Polyram, magnesium sulfate (Epsom salts), liquid pesticides or emulsifiable formulations, and certain wettable sulfur formulations. If there is doubt concerning compatibility of Ca with pesticides in foliar sprays, consult the manufacturer of the pesticide or use other sources of Ca known to be compatible.


In summary, the extent and seriousness of bitter pit depends on many factors, including some weather and crop factors outside the grower’s control.

However, there are many practices that minimize the extent of bitter pit, reducing fruit loss at harvest and during storage. This increases the return to growers, particularly for varieties prone to developing this disorder. All of these factors should be considered in orchard management to produce high-quality fruit.

For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca

Back to the idea of mulching with woodchips its a fantastic idea today it retains moisture and nutrients and encourages worms! Everything is very good with wood chip mulch when first applied. Keep in mind 20 years down the road what’s a fantastic idea today may not be fantastic later. If excessive nutrients begin building up from woodchips breaking down in the decomposition process it can be a problem. As an example I used woodchips mixed with chicken manure in a compost pile. The idea was the woodchips would help absorb excess nitrogen in the decomposition of the woodchips. Several years later the woodchips and chicken manure would be an exceptional compost and the nitrogen that was locked up would be available again. That delayed nutrient release is common of wood chips and manure. Wood chips mixed in the soil use nitrogen but on top of the ground do not use nitrogen according to experts. In my case having to much chicken manure to use at the time after cleaning out a hen house mixing it with wood chips made sense. Robbing the manure of nitrogen for the decomposition process was the idea.


Early fall applications of quick release N. may be the best way to direct it to spur leaves, which is where you want it after trees reach their desired size. When you want them bigger, you are served well to supply ample N into mid-summer- a very late summer or early fall app may also be useful to assure even vegetative buds have plenty stored going into winter for vigorous spring growth. Otherwise the roots won’t pick it up until the soil is warm and aerobic enough.

Cornell suggests earlier apps of calcium than what is suggested by Canadians- soil applied calcium seems to have little affect at reducing bitterpit. It is possible that too much potassium can reduce calcium intake into the fruit itself and woodchips are loaded with soluble K.

One thing I should know but don’t- does calcium in the tank destroy the effectiveness of Captan? I have even searched for the answer but not found it. It would be difficult to follow the Cornell early CA apps if it can’t be tank mixed with Captan for me. This is why I’ve only done July-Aug apps of it so far and it seems to work.



In the past @Olpea and I discussed this very thing about chemical and calcium. Hard water does reduce the effectiveness of chemicals we know that. We also know if you added vinegar to the water your chemicals would effectively become stronger but not better. Adding vinegar is not a good thing but read the attached article and it explains why. This is not unknown to the farming community in our part of the world as chemicals can become very expensive and they want to know they are working properly https://www.croplife.com/crop-inputs/herbicides/herbicide-application-effective-management-of-hard-water-in-spray-solutions/
Ammonium sulfide additions may be added and those impact calcium only but not magnesium and others https://extension.psu.edu/ph-and-water-modifications-to-improve-pesticide-performance
"pH and Water Modifications to Improve Pesticide Performance

The water carrier of pesticides may influence the overall effectiveness of the pesticide used for control. Knowing some basics of water can be useful in protecting yields in crops.



I read with interest an article from an Pesticide Education Specialist Reeves Petrof from Montana State University regarding pesticides and water. Here is a brief overview of key points Reeves Petrof details in his fact sheet. I have also added items for the Penn State Vegetable guide as well as the Penn State Water Resources Team.

Pesticides are chemicals and when introduced into water may react depending on the hardness of the water. Cations (+) and anions (-) are similar to magnets. Hard water typically has a positive charge so if a pesticide is an anion or negative charge they will bind together and will not separate once applied to the pest in question. This reduces the effectiveness of the product. A simple water test of your primary spray water supply now will determine how you manage the water this season. Most farms water sample for either dairy, swine and poultry so a water test should be relatively simple to locate and or gain.

Here is a simple table to the hardness of water. Hardness is the makeup of the minerals in the water and may contain either Ca++, Mg+++ or Fe+++

Softbelow 50 ppmMedium Hard50-100 ppmHard100-200 ppmPesticide effects?

I have had several herbicide and insecticide failures that I could not diagnose for certain but I had suspected issues with the water. All of the cases that I was involved in happened to be in spray tanks that were filled and then sat overnight before being emptied and I had theorized a reaction with the water rendered the pesticide useless. One take home message is to avoid allowing certain pesticides to remain in the tank for any long term time frame. One example I was involved with included Dimethoate which can react in literally minutes after mixing pending the water pH. Salt-formulated herbicides such as Roundup (glyphosate), Poast (sethoxydim), Pursuit (imazethapyr), and Liberty (glufosinate) are subject to being bound in the water and for this reason many labels instruct to lower the pH of the water to ensure optimum performance. These minerals may bind with salts of certain herbicides and with some surfactants to form an insoluble salt. These insoluble salts then “fall out" out of solution decreasing herbicide or surfactefficiency. In the case of isopropylamine salt formulations of glyphosate, the positively charged cations of calcium (Ca2+) and magnesium (Mg2+) salts compete with the isopropylamine in the formulation for association with the glyphosate anion (negatively charged). This results in the herbicide having a greater difficulty absorbing into the plant leaf.

In addition, research has shown that extremely hard water, 600 ppm (35 grains/US gallon), can almost completely antagonize 2,4-D amine applied at a low rate of about 4 to 8 ounces per acre. Hard water also affects fungicides and insecticides so it is important to read the labels of all products to determine ideal pH ranges.

Here is a small list of some common products in addition to the glyphosate formulations which is more widely recognized.

Common nameTrade nameHalf-life at different pH valuesFungicide examplesPropiconazoleTiltMost effective in pH 5 to 9; use within 12 to 16 hoursCaptanOrthocidepH 5 = 32 hours, pH 7 = 8 hours, pH 8 = 10 minutesInsecticide examplesCarbarylSevinpH 7 = 24 days, pH 8 = 2.5 days, pH 9 = 1 dayDimethoateCygonpH 4 = 20 hours, pH 6 = 12 hours, pH 9 = 48 minutesPermethrinPounceOptimum stability pH 4Herbicide exampleParaquatGramoxone Extranot stable in pH above 7Plant growth regulatorGibberellic AcidPromalinA buffered wetting, final spray should not exceed pH 8So how do you reduce the hardness of the water?

Note: Acidifiers should not be used in conjunction with some organo-silicone adjuvants as increased acidity may enhance chemical breakdown of the adjuvant. In addition, sulfonyl urea herbicides (Accent, Harmony etc) can degrade in acidic environments below 7.

Read the label!

The most widely used materials to help with hard water is AMS. With the Xtend technologies, it is critical to read the label as additional water modifications can can change the dicamba and change the acid to a more volatile form.

  1. Ammonium Sulfate (NH4SO4).

Ammonium sulfate (AMS) has been used successfully to increase herbicide efficacy on a broad spectrum of weed species. This is particularly true for the weak-acid herbicides like Roundup (glyphosate), 2-4-D, Pursuit (imazethapyr), Poast (sethoxydim) and Basagran (bentazon). The AMS adjusts the pH so that more of the active herbicide is transported across the leaf surface and into the plant. An added benefit is that sulfate ions (SO4) bind up with hard water minerals. In addition, ammonium-herbicide combinations are more easily absorbed by some weed species. A general rule-of-thumb for adding AMS is the addition of 2% AMS by weight or 17 pounds of dry AMS per 100 gallons of water for most applications.

AMS should be added to the spray carrier solution prior to the herbicide and always, consult the pesticide label for mixing instructions. There may be limitations on the use of fertilizer-based surfactants. The industry has strived to make this process simpler for the applicator by liquifying AMS and there are numerous products that are liquid AMS (Turbo and numerous others) and each product needs to be added at the appropriate rate according to the label to effectively bind the hard water. They can range from a per acre to a per 100 gallon dilution. There are some new products in this arena that either are AMS and or UAN derrivitives. Halo is relatively new the area and has been used to replace AMS, Turbo, Request, Choice, and other similar products.

  1. Organic Acids.

A very effective treatment is utilizing citric acid. The addition of an organic acid such as food grade citric acid will effectively remove hard water ions from solution. Organic acids are effective because the conjugate base (negative portion) of the acid binds to and removes positively charged cations from solution. A weak acid, such as citric acid, will provide a stronger conjugate base, and therefore, will be more effective than a strong acid such as nitric or hydrochloric acid. The addition of the organic acid will also lower the spray solution pH because of the addition of hydrogen (H+) ions. Organic acid is added to the water carrier prior to the addition of the herbicide. A use rate of 2.2 pounds of citric acid per 100 gallons of water should be adequate for water with 250 ppm of Ca2+.

From my travels, many poultry growers have citric acid on hand for use in the poultry watering system.

  1. Urea Ammonium Nitrate (UAN)

Some sources of Urea Ammonium Nitrate (UAN) may also reduce the hardness but not as effective as AMS and this is why AMS is preferred over UAN. Some UAN utilizes a Sulfuric Acid source to add Sulfur to the fertilizer mixture and may enhance the acidification from UAN.

Use the following general guidelines once you have determined the pH is of your spray water. Remember, read the pesticide label.

pH 3.5-6.0 Satisfactory for most spraying and short-term (12 to 24 hours) storage of most pesticide mixtures in the spray tank. Read the label. Not suitable for sulfonylurea (Accent, Harmony) herbicides.pH 6.1-7.0 Adequate for immediate spraying of most pesticides. Do not leave the spray mixture in the tank for over 1 to 2 hours to prevent loss of effectiveness.pH 7.0 and higher. Add buffer or acidifier.

You can offset the effects of water pH by adding certain adjuvants (additives) that can either change the pH or your spray mixture or maintain (buffer) the levels of dissolved solids and organic particulate matter … dirt! These soil particles decrease Roundup (glyphosate) and paraquat activity and can cause equipment wear. This type of antagonism cannot be corrected by adding AMS or an organic acid. Always choose a water source that is free of dirt, grit, and organic matter.

Adjuvants and Surfactants

Water softening additives designed for pesticide applications are available to offset hard water problems. While nonionic surfactants will generally enhance herbicide activity on most weed species, they will not overcome the antagonism between salt-based herbicides and hard water. Therefore, under hard water conditions, AMS or organic acids should be used in conjunction with nonionic surfactants to maximize herbicide absorption. Read the label of surfactants that you buy. Some AMS surfactants already have a nonionic surfactant added pH if it already at the desirable level. Here is an older, however useful, fact sheet that UAP has produced with Loveland regarding its LI 700 UAP product that is a penetrant as well as a hard water solution. This product is designed to aid in penetration as well as reduce pH. I am not promoting their product, rather the fact that they have a large list of pesticides and their pH requirements. There are numerous other products similar to this product so check with your supplier for these products and use.

Final ThoughtsThe key is to read the labelGain a water testFill the tank half to 2/3rd full and add the water treatment before adding any of the products that are affected by the pH or hardness.Add other products in the right order to ensure mixing.

By following some simple rules the maximum effectiveness of herbicides, insecticides, fungicides and plant growth regulators may be achieved and avoid failures in the field."

" Herbicide Application: Effective Management of Hard Water in Spray Solutions

Avatar for Matt Hopkins By David VincentMay 14, 2019

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Water quality is a frequently overlooked factor that can adversely affect the performance of pesticides, especially herbicides. Besides pH, water “hardness” is a key concern, with much of the agricultural water sources across the U.S. exhibiting high concentrations of calcium, magnesium, iron, sodium, and aluminum. These hard-water cations — especially calcium and magnesium — can wreak havoc in a spray tank when not managed.


Weak acid herbicides, such as glyphosate and 2,4-D, are most susceptible, but no herbicide chemistries are completely immune to the negative effects of hard water, including dicamba and sulfonylurea (SU) herbicides. Use of ammonium sulfate (AMS) in spray solutions only counters the effects of calcium hard-water cations, providing no protection whatsoever from magnesium and the others.

Herbicide Application: Effective Management of Hard Water in Spray Solutions

Iowa applicator Jason Winegar of Nutrien Ag Solutions has been able to eliminate having to handle and pour 50-pound bags of ammonium sulfate into his sprayer while in the field.

“When you do a good job of addressing hard water, the herbicides mix, blend, and apply much better,” says Jason Winegar, an applicator at Nutrien Ag Solutions in Dunlap, IA. “You get more uniform spray coverage, better adhesion to and penetration of herbicides to target weed species, and more control over drift by better managing spray droplet size and patterns.”

For eight years Winegar has driven floaters and high-clearance sprayers over at least 50,000 acres of corn and soybeans annually. He makes burndown, preemergence, and post-emergence over-the-top herbicide applications and often covers the same ground at least twice during any given growing season.

With a staff of five or six applicators, this Nutrien Ag Solutions location provides custom-application services on at least a quarter-million acres every year. Herbicides routinely applied include glyphosate, Accuron, Diflex, Caprino, Harness Extra, 2,4-D, and dicamba. In addition to his application work, Winegar also works in the company’s mixing and blending facilities.

Multiple Modes of Action

Water with high concentrations of magnesium and calcium is a challenge to manage when applying herbicides. Instead of AMS, Winegar uses a water conditioner, Choice Trio from Loveland Products, which offers three modes of action: sequestering, synthetic chelating, and complexing. The adjuvant, he says, reduces the effects of hard-water cations on herbicide performance, eliminating the need to use AMS.

“We can’t run AMS through the liquid system at the plant because it plugs things up,” Winegar says. “Instead, I have to add it directly to the sprayer while nursing in the field. This means I have to manually open 50-pound bags of granular AMS and pour them into the sprayer. It’s a handling issue that really slows us down when we need to focus on covering as many acres as quickly as possible. We can load the Choice Trio at the plant and do away with the AMS field-loading delays.”

Choice Trio is a liquid formulation available in 2.5-gallon pack sizes. Besides interfering with herbicide efficacy, hard water that isn’t properly buffered also takes its toll on equipment, including pumps, seals, screens, filters, and hoses. “This is another economic downside of hard water,” Winegar says. “It drives up maintenance costs because these items have to be replaced more often.”

Enhanced Grove Care

Commercial applicator Richard Byrd in South Florida makes herbicide applications in an area where water is exceptionally hard. Operating under Richard Byrd Caretaking, he conducts herbicide applications on 1,800 to 2,000 acres of orange groves, making three application trips per year for a combined 5,500 to 6,000 treated acres.

This work includes chemical mowing of grove middles and weed control in the tree line with residual and contact herbicides, including Karmex, Solicam, glyphosate, Tree Vix, and MSO. He uses high-end application equipment, GPS positioning, and other state-of-the-art technology.

“When I’m running flat out, I mix and apply 1,400 to 1,500 gallons of herbicide daily,” Byrd says. “Due to the concentrations of magnesium in the surface water I use as a carrier, I would have to stop two or three times a day — about every 400 to 500 gallons — to clean clogged filters. Then, a few weeks after application, there would be strips in the middles where weeds had not been controlled due to clogged nozzles or herbicide that didn’t mix very well.”

Herbicide Application: Effective Management of Hard Water in Spray Solutions

A comparison of filters before and after Choice Trio use.

Another hard-water casualty was the toll it took on spray tanks. A nasty black substance would build up on tank bottoms and walls following herbicide applications. This was residue from the magnesium in the water, and cleaning it required a substantial amount of elbow grease. In 2015 Byrd began using Choice Trio adjuvant to better address the mixing, application, and staining issues associated with hard water.

“I haven’t had to clean the magnesium and chemical residues out of any spray tanks in the four years since I started using the adjuvant,” he says. “I also have greatly reduced — almost eliminated — the downtime associated with clogged filters, screens, and nozzles, as well as the misapplications of herbicides due to mixing issues.”

Byrd says 99.9% of mixtures in the tank are applied and that mixtures stay in suspension longer. “Any herbicide remaining in the tank after application is wasted money,” he notes. “And any herbicides that don’t mix properly are costing you money as well.”

Byrd adds that taming his hard water has had a profound effect on equipment maintenance costs. “I’m getting at least an extra year out of my pump seals, as well as from my pumps,” he says.

Other adjuvants that Byrd routinely relies upon include E-Z Mix when applying powdered or granular herbicides and LI 700 as a sticker/spreader to reduce drift, improve spray droplet retention by adhesion and spreading, and increase herbicide penetration without cuticle disruption. He no longer uses liquid AMS, he says, because he doesn’t have to."

In conclusion calcium sprays should be separate from others. Calcium is a cation which readily bonds to anions neutralizing them. Progressively more soil Scientist and medical
scientist are aware of the importance of these relationships between cations and anions
" AY-238

Soils (Fertility)

Purdue University
Cooperative Extension Service
West Lafayette, IN 47907

Fundamentals of Soil Cation Exchange Capacity (CEC)

David B. Mengel, Department of Agronomy, Purdue University
Soils can be thought of as storehouses for plant nutrients. Many nutrients, such as calcium and magnesium, may be supplied to plants solely from reserves held in the soil. Others like potassium are added regularly to soils as fertilizer for the purpose of being withdrawn as needed by crops. The relative ability of soils to store one particular group of nutrients, the cations, is referred to as cation exchange capacity or CEC.

Soils are composed of a mixture of sand, silt, clay and organic matter. Both the clay and organic matter particles have a net negative charge. Thus, these negatively-charged soil particles will attract and hold positively-charged particles, much like the opposite poles of a magnet attract each other. By the same token, they will repel other negatively-charged particles, as like poles of a magnet repel each other.

Forms of Nutrient Elements in Soils

Elements having an electrical charge are called ions. Positively-charged ions are cations; negatively-charged ones are anions.

The most common soil cations (including their chemical symbol and charge) are: calcium (Ca++), magnesium (Mg++), potassium (K+), ammonium (NH4+), hydrogen (H+) and sodium (Na+). Notice that some cations have more than one positive charge.

Common soil anions (with their symbol and charge) include: chlorine (Cl-), nitrate (NO3-), sulfate (S04=) and phosphate (PO43-). Note also that anions can have more than one negative charge and may be combinations of elements with oxygen.

Defining Cation Exchange Capacity

Cations held on the clay and organic matter particles in soils can be replaced by other cations; thus, they are exchangeable . For instance, potassium can be replaced by cations such as calcium or hydrogen, and vice versa.

The total number of cations a soil can hold–or its total negative charge–is the soil’s cation exchange capacity. The higher the CEC, the higher the negative charge and the more cations that can be held.

CEC is measured in millequivalents per 100 grams of soil (meq/100g). A meq is the number of ions which total a specific quantity of electrical charges. In the case of potassium (K+), for example, a meq of K ions is approximately 6 x 1020 positive charges. With calcium, on the other hand, a meq of Ca++ is also 6 x 1020 positive charges, but only 3 x 1020 ions because each Ca ion has two positive charges.

Following are the common soil nutrient cations and the amounts in pounds per acre that equal 1 meq/100g:

Calcium (Ca++) - 400 lb./acre Magnesium (Mg++) - 240 lb./acre Potassium (K+) 780 lb./acre Ammonium (NH4+) - 360 lb./acre

Measuring Cation Exchange Capacity

Since a soil’s CEC comes from the clay and organic matter present, it can be estimated from soil texture and color. Table 1 lists some soil groups based on color and texture, representative soil series in each group, and common CEC value measures on these soils.

Table 1. Normal Range of CEC Values for Common Color/Texture Soil Groups.

CEC in Soil groups Examples meg/100g ----------------------------------------------- Light colored sands Plainfield 3-5 Bloomfield Dark colored sands Maumee 10-20 Gilford Light colored loams and Clermont-Miami 10-20 silt loams Miami Dark colored loams and Sidell 15-25 silt loams Gennesee Dark colored silty clay Pewamo 30-40 loams and silty clays Hoytville Organic soils Carlisle muck 50-100 -------------------------------------------------

Cation exchange capacity is usually measured in soil testing labs by one of two methods. The direct method is to replace the normal mixture of cations on the exchange sites with a single cation such as ammonium (NH4+), to replace that exchangeable NH4+ with another cation, and then to measure the amount of NH4+ exchanged (which was how much the soil had held).

More commonly. the soil testing labs estimate CEC by summing the calcium, magnesium and potassium measured in the soil testing procedure with an estimate of exchangeable hydrogen obtained from the buffer pH. Generally, CEC values arrived at by this summation method will be slightly lower than those obtained by direct measures.

Buffer Capacity and Percent Base Saturation

Cations on the soil’s exchange sites serve as a source of resupply for those in soil water which were removed by plant roots or lost through leaching. The higher the CEC, the more cations which can be supplied. This is called the soil’s buffer capacity .

Cations can be classified as either acidic (acid- forming) or basic. The common acidic cations are hydrogen and aluminum; common basic ones are calcium, magnesium, potassium and sodium. The proportion of acids and bases on the CEC is called the percent base saturation and can be calculated as follows:

Total meq of bases on exchange sites Pct. base =(i.e., meq Ca++ meq Mg++ + meq K+) saturation ------------------------------- x 100 Cation exchange capacity

The concept of base saturation is important, because the relative proportion of acids and bases on the exchange sites determines a soil’s pH. As the number of Ca++ and Mg++ions decreases and the number of H+ and Al+++ions increases, the pH drops. Adding limestone replaces acidic hydrogen and aluminum cations with basic calcium and magnesium cations, which increases the base saturation and raises the pH.

In the case of Midwestern soils, the actual mix of cations found on the exchange sites can vary markedly. On most, however, Ca++ and Mg++ are the dominant basic cations and are in greater concentrations than K+. Normally, very little sodium is found in Midwestern soils.

Relationship Between CEC and Fertilization Practices

Recommended liming and fertilization practices will vary for soils with widely differing cation exchange capacities. For instance, soils having a high CEC and high buffer capacity change pH much more slowly under normal management than low-CEC soils. Therefore, high-CEC soils generally do not need to be limed as frequently as low-CEC soils; but when they do become acid and require liming, higher lime rates are needed to reach optimum pH.

CEC can also influence when and how often nitrogen and potassium fertilizers can be applied. On low-CEC soils (less than 5 meg/20000g), for example, some leaching of cations can occur. Fall applications of ammonium N and potassium on these soils could result in some leaching below the root zone, particularly in the case of sandy soils with low-CEC subsoils. Thus, spring fertilizer application may mean improved production efficiency. Also, multi-year potash applications are not recommended on low-CEC soils.

Higher-CEC soils (greater than 10 meg/100g), on the other hand, experience little cation leaching, thus making fall application of N and K a realistic alternative. Applying potassium for two crops can also be done effectively on these soils. Thus, other factors such as drainage will have a greater effect on the fertility management practices used on high- CEC soils.


The cation exchange capacity of a soil determines the number of positively-charged ions cations-that the soil can hold. This, in turn, can have a significant effect on the fertility management of the soil.


Cooperative Extension work in Agriculture and Home Economics, State of Indiana, Purdue University and U.S. Department of Agriculture cooperating: H.A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the acts of May 8 and June 30, 1914. The Cooperative Extension Service of Purdue University is an equal opportunity/equal access institution.

It said in the article above.


For anyone not familiar captan is one of the fungicides sprayed to prevent fruit problems. https://extension.psu.edu/tree-fruit-disease-toolbox-fungicide-resistance-management

"Tree Fruit Disease Toolbox - Fungicide Resistance Management

Resistance has sometimes resulted in pest-management-program failures. Below are presented tactics to help delay resistance to fungicides.


UPDATED: JUNE 19, 2018

Understanding Types of Fungicides

Pesticides used for managing fungi-caused fruit diseases are either fungicidal (they kill fungi) or fungistatic (they inhibit fungal growth). Fungicides can be separated into two categories: protectants and systemics.

Protectant fungicides protect the plant against infection at the site of application. Their characteristics are as follows:

They provide protection against infection.They do not penetrate into the plant.They require uniform distribution over the plant surface.They require repeated application to renew deposit.They have a multisite mode of action against fungi.Fungi are not likely to become resistant to protectant fungicides. Some common protectant fungicides are Bravo, captan, copper, Dithane, Manzate, Polyram, sulfur, and Ziram.

Systemic fungicides prevent disease from developing on parts of the plant away from the site of application. Their characteristics are as follows:

They penetrate into the plant.They move within the plant.They control disease by protectant and/or curative action.They often have a very specific mode of action against fungi. Some systemic fungicides are Elite, Flint, Indar, Rally, Merivon, Orbit, Pristine, Procure, Rubigan, and Sovran.Cultural Control and Fungicide Use Patterns

Due to environmental conditions, disease is inevitable in the Mid-Atlantic growing region and use of chemical controls is a necessity; however, following cultural practices that favor decreasing disease pressure will help decrease the opportunity for resistance. Using resistant varieties, minimizing tree stress, and maintaining proper soil fertility reduces disease incidence since pathogens do not reproduce well on trees that are less susceptible to disease. As a result, the chance of resistance decreases. Avoid selecting sites with high disease pressure since this increases the chance of selecting for resistant fungi. Using dormant copper sprays and removing inoculum sources such as leaves (using urea or a flail mower), mummified fruit, and dead twigs/branches reduces the initial pathogen population. When using fungicides, use only when needed since this avoids unnecessary selection for resistant populations. It is important to be sure sprayers are appropriately calibrated and covering trees effectively. Achieving good spray coverage, tank-mixing with protectants, and alternating fungicides with different modes of action (FRAC group) reduces populations exposed to selection.

Fungicide Resistance Issues and Mitigation Strategies for Specific DiseasesApple scab and brown rot

Fungicides in FRAC Groups 3, 7, 9, and 11 are highly effective against scab infection on apples and brown rot on stone fruit. However, apple scab and brown rot fungi can become resistant to these fungicides, especially if any of them are continually applied alone. Growers using one of these fungicides to control apple scab or brown rot must be certain to not only alternate it with an unrelated fungicide but also use it in combination with a broad-spectrum fungicide, like captan, metiram (Polyram), mancozeb, Ziram, thiram, sulfur, or ferbam. Another strategy to prevent resistance is to alternate the use of these materials throughout the season. The less any one of them is used in an orchard during a given season, the lower the chances that resistance will develop. At the present time, we know fungi causing apple scab and brown rot have shown high tolerance to fungicides in FRAC Group 11. As a result, growers are cautioned when using fungicides in this class, especially when it is not included as a premix. These fungicides should be avoided during peak primary apple scab spore dispersal, which is from late pink through petal fall.

Mitigating fungicide resistance for apple scab

Using cultural controls, such as removing inoculum sources (fallen leaves), is important for decreasing disease incidence; however, during seasons where the disease pressure is high (frequent rains, warm temperatures), fungicide applications will be important. It is critical to monitor disease conditions since this will play a crucial role in deciding which fungicides to use and when. In addition, if the alternate row middle (ARM) method is being used, it is very important to not stretch intervals, especially during frequent warm and rainy conditions. Sometimes this may mean shrinking intervals to five days, especially if disease conditions are favorable. There have been incidences where apple scab “broke through” as a result of stretching ARM intervals too long during very wet periods.

From green tip through tight cluster

Scab spores will begin to be dispersed from overwintering leaves starting at green tip; however, the spore numbers will be low, gradually increasing over time. If conditions are dry, focus on managing powdery mildew by using products such as Indar, Rally, Topguard/Rhyme, or sulfur tank-mixed with a broad-spectrum fungicide (EBDC, ferbam, metiram, ziram). Dry weather plus low scab spore numbers equals low disease pressure. Although some strong powdery mildew products are not as effective against scab, a broad-spectrum fungicide will keep the disease in check. If disease conditions are favorable for scab (warm and wet), then consider using other fungicides from FRAC Groups 3 or 9, such as Indar, Inspire Super, Procure/Trionic, Scala, or Vangard, during this period. Be sure to rotate FRAC Groups. Growers are highly encouraged not to use the FRAC Group 7 fungicides during this time period; these fungicides are best saved for peak apple scab pressure, which is from pink through petal fall.

From pink through petal fall

Scab spores will start to peak (the maximum number of available spores dispersing from the overwintering leaves) beginning late pink and will remain high through approximately late petal fall. In our experience with monitoring scab spore dispersal from overwintering leaves, available scab spores remain high (more than 10,000) for approximately two weeks (from pink through petal fall). During this time, it is best to use FRAC Group 7 (SDHI) fungicides, such as Aprovia, Fontelis, Luna Sensation, Luna Tranquility, Merivon, Pristine, or Sercadis, and tank-mix with a broadspectrum fungicide. Limit FRAC Group 7 fungicides to two applications during this period of high disease pressure. A maximum of four complete applications are allowed per year for FRAC Group 7 fungicides. Save two FRAC Group 7 fungicide sprays (if possible) for the end of the season when Luna Sensation, Merivon, or Pristine should be applied in order to mitigate late season and storage fruit rots.

From post petal fall through second cover

Although the number of overwintering scab spores drastically decreases after petal fall, spores are still available and can wreak havoc, especially if conditions favorable for disease are present. During this time, use products from FRAC Group 3 and 9, such as Inspire Super, Indar, Rally, Procure/Trionic, Scala, or Vangard, plus a broad-spectrum fungicide. One recommendation is to use an EBDC through first or second cover and then switch to captan for the later summer cover sprays. Use products that may have a long PHI (such as Scala) earlier rather than later. These products could also be used in rotation with the FRAC Group 7 fungicides that are used from pink through petal fall.

Mitigating fungicide resistance for brown rot

Many factors influence brown rot development. During dormancy, removal of brown rot blossom blight cankers and fruit mummies will decrease the number of available spores during the season. Green fruit are not susceptible to infection by the brown rot pathogen. However, immature fruit that are not properly pollinated or become injured can become infected and begin to rot. Remove any infected green fruit and drop them to the ground. Near harvest, as fruit are maturing, drop any rotting fruit to the ground to prevent fruit from becoming mummies, thereby reducing overwintering inoculum for next year.

Bloom through cover sprays

The relative efficacies of current fungicides available are listed in Table 4-14. Depending on disease conditions during bloom, one or two sprays will be needed for protection from blossom blight caused by the brown rot pathogen. Research from Rutgers has shown that captan cover sprays will adequately drop the number of available spores that could cause disease when harvest nears.

Preharvest sprays for brown rot

If frequent rains continue throughout the summer and harvest season, then a three-spray preharvest program is highly recommended. The recommended timing for this program is 18 days, nine days, and one day preharvest, with a final captan cover spray at 28 days preharvest. Note that the final preharvest spray can be applied immediately before the first picking, or alternatively between the first and second picking; the idea is to provide protection throughout the handling process. Of course, the fungicide used at this time must have a zero- or one-day PHI and appropriate REI. For resistance management reasons, a minimum of two different chemistries should be applied to each cultivar block (alternated). However, use of three different chemistries is strongly recommended given that some of these chemistries are rated as high risk for development of resistance. An excellent three-spray program that utilizes all three chemistries is Gem (FRAC Group 11), Indar (FRAC Group 3), and Fontelis (FRAC Group 7). For those fungicides composed of two active ingredients, simply alternate with the third chemistry. For example, apply a fungicide with FRAC Groups 7 and 11, FRAC Group 3, and FRAC Groups 7 and 11. As you progress through the harvest season spraying different cultivar blocks, simply continue with the rotation.

Powdery mildew

Frequent applications of fungicide may be required for mildew control. Fungicides in FRAC Groups 3 and 7 are effective for controlling powdery mildew. There are presently no documented cases of apple powdery mildew resistance to these materials.

Cedar apple rust

Only a brief part of the life cycle of the cedar apple rust fungus is spent on apple trees. Infection of apple leaves or fruit occurs between the pink and first cover spray periods. The cedar apple rust fungus survives 19 months or longer on red cedar. The contact between the fungus and the fungicide applied to apples is relatively short, reducing the potential for resistance to develop. If a resistant cedar apple rust fungus does develop, it must also survive on red cedar. Therefore, resistance of the cedar apple rust fungus to any fungicide is not likely.

Summer diseases on apple

Although resistance has not been reported for fruit rots or sooty blotch and flyspeck, it is important to be proactive by rotating fungicides and tank mixing with a broad spectrum chemical when controlling these diseases.

Frequently asked questions about fungicide resistanceDoes the type of fungicide used affect the potential for a fungus to develop fungicide resistance?

Broad-spectrum fungicides like copper, captan, and sulfur act by interfering with several of the fungus’s vital life functions. These fungicides have multiple modes of action, which allows little chance for resistance since the fungus must undergo multiple changes to counteract the fungicide.

Systemic fungicides like Inspire Super, Vangard, Scala, Flint, Sovran, Merivon, Pristine, Luna Sensation, Luna Tranquility, Fontelis, Rubigan, and Rally are highly effective against many tree fruit diseases. They are single-target-site fungicides interfering with one vital life function, so one change is needed for the fungus to become resistant. Thus, the potential for resistance to these fungicides is much greater than to broad-spectrum fungicides.

How do fungi develop resistance to a fungicide in an orchard?

As previously discussed, resistance is more likely to develop against fungicides that have a single mode of action, especially if they are used alone for a long time. In the orchard, resistant fungi may occur naturally in very small numbers even before the fungicide is first used. When a fungicide is applied, it reduces the number of susceptible apple scab and brown rot fungi. The few scab and brown rot fungi that are resistant to the fungicide are able to increase in number. As the fungicide is repeatedly used, the number of resistant fungi increases. The fungicide becomes less effective as the fungus becomes more tolerant to it.

Are resistant apple scab fungi and brown rot “super” fungi?

No, apple scab and brown rot fungi that are resistant to certain fungicides are still susceptible to others that have a different toxic action against the fungi. Using fungicide mixtures will delay the buildup of resistant scab and brown rot fungi. Mixtures are most effective when used before resistance becomes a problem. Alternating chemicals that have different modes of action/FRAC code is another strategy to prevent resistance from developing.

Can sensitivity can return to certain fungicide classes?

Fungicides are not created equal when discussing persistence of tolerance of the fungus to a particular class of fungicides. For instance, sensitivity can return to fungicides in the FRAC Group 3 if these fungicides are not used for a period of time. This is due to resistance being a fitness cost to the fungus, i.e. the fungus will not maintain resistance since it will prevent the fungus from surviving over time. In contrast, sensitivity will not return to fungi that are resistant to the fungicides in FRAC Group 11 since the nature of the resistance is based on the mutation of one gene that is stable and not linked to fitness.

The Future of Tree Fruit Disease Control

Growers can prevent resistance by practicing good cultural control methods, using fungicide mixtures, tank-mixing with a broad-spectrum protectant, and alternating chemicals by FRAC Group code (“spraying by the numbers”).

Spraying by the Numbers: Fungicide Resistance Management —These downloadable tables will help you to avoid resistance by “spraying by the numbers.”


Really great information posted here. So much to take in and think about. I would really hate to have to spray calcium on my trees. That seems like of extra work for a recreational apple grower to do just to get apples to enjoy. If I had a commercial operation it would be a must to do and I could justify the cost. Placing crushed oyster shells is, to me, a lot easier and cheaper to do. I will do that to my trees though.
Again, great information. TY all for posting this helpful information.

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The average orchardist isn’t looking for perfect apples most of the time. In Kansas I’m OK with apple cider.

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There are plenty of delicious varieties not prone to bitterpit, so if you can keep your fruit growing from becoming an absolute obsession with the “need” to grow any apple you happen to love, regardless of effort, you will be fine- most sites, most seasons. For many, Honeycrisp and Jonagold won’t be worth the effort. Red Prince Jonagold is a lot like Honeycrisp and I “need” some in my fridge to get me through winter.


Good points. The only reason I have Honeycrisp is my family did a taste test years ago of apples they liked. I planted some trees of the varieties we could all pretty much agree on. The varieties we tried were all from a local orchard grower.
I may have gotten some bitterpit on a couple of other apple varieties I grow. I will keep track of the ones that get it. It is not something I get every year.
I know I threw the apples away that had it. However, I do not think it was on all the apples on that tree, only some of them.
I am not sure if that is normal or not- only some apples on the tree get it and other do not.

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