The dreaded F word (Fireblight) is showing up in our orchards

Was your Canadian Reinette considered synonymous with Pomme Gris?

I have seen some sources claim those apples are one and the same.

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They are very different apples, CR is big PG is small, CR is round, PG is flattened, etc.

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Thanks. There is some misinformation out there on the interwebs!


I never saw fireblight here before but I was away for a week and when I returned all my pears were covered with it. Last year was their first year to fruit. I thought the varieties I planted were highly resistant (Keiffer, Orient, Pineapple, Moonglow) but looks like that didn’t save me. I cut out some of it but a lot is too high to reach with the equipment I have. At this point I’m just hoping some of the trees survive. It feels like a kick in the gut.


Sorry to hear that. I know your pain having had the same thing happen in the past. When it gets bad you feel powerless.

While the standard recommendation is to prune it all out, some people just leave tip strikes alone and are of the opinion it doesn’t make a huge difference. I am in-between, if its convenient I will prune it out but I don’t go after every single strike. Any big limb strike I remove as those seem to ooze the most.

This spring is the worst for me in the last five or so years. Its still only minor single tip and blossom strikes in nearly all spots so no panic yet.


So as far as conditions go for FB to really get going: I gather you need warm/wet conditions? Is humid air enough? Or so you need dew or rain?

I did a hook around the block and checked the pear the had bad blossom blight last year with ominous oozing pears midsummer. No signs of it this year. But today was our 1st or 2nd really warm (84F) day where we got a bit of humdity.

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As I drive around in southern California, I see flowering pears and pyracantha in parking lots and industrial landscapes with about 15% FB damage per plant; i.e., the die-back is about 8 inches on half the branches.

I haven’t detected FB damage on my susceptible plants yet this year. As mentioned in other threads, I do have an on-again off-again winter-spring cadence with my deciduous trees – lasting from around November through March because there is no “hard” freeze here. I’ve learned to spray with copper (Kocide 3000) at times of leaf-fall and anti-biotic (Agrimycin) during times of leaf bud. However, I do expect my Hood Pear will show FB sign before Fall.


Fireblight is one of the most mysterious plant illnesses ever encountered. My observations have been the years you expect it you won’t see it and the years you don’t expect it you will. Personally I believe it’s ever present waiting for a disease spreading agent like insects. In my case the 17 year cicada caused the worse fireblight I’ve ever experienced. Callery pears are either resistant to FB or not like normal pears but the ones I have never showed a strike from it. To make matters more complicated there are different strains of fireblight so never presume to know how bad someone’s battle is until you live where they do and fight their strain of FB because it takes trees down and does not discriminate which ones at times. I had plumblee which is reportedly highly FB resistant in the south killed to the ground when the tree reached several feet of growth in a single year ( last year). I’m convinced it is a great tree and I made backup grafts that were fine a few feet away. The FB Bacteria problem is nearby home orchards leave it unchecked. Some of their trees are resistant so they live through it and birds and insects bring it here. Once a tree blooms and fruits it weakens the trees immunity and it’s more susceptible to FB. Poor soil does the same thing in my observations but I have no hard science to confirm my claims. Time will confirm if I’m getting better at treating it or not but I’m under the impression some trees are magnets and I graft them over. I had a seedling bartlett that was a magnet. Young trees are more likely to get FB than old trees because FB only attacks rapidly growing tissue. Old trees loose vigor as they age so they will seem immune to FB but they are not. Don’t over fertilize your trees because that’s trouble waiting to happen. Copper is a good anti bacterial and I’m thankful the people here convinced me of that. No one likes to spray their trees with heavy metals and I’m no exception and I fought it as long as I could. Once or twice a year copper sprays are very effective! My theories are ever changing and one thing I’ve seen is that plumblee was killed to the ground just like my clapps favorite. Seckel can get FB and so can kieffer. Every tree has it’s own characteristics one of which is kieffer corks off FB so right now I grafted abate fetel on kieffer as a test. I grafted forelle high up on ohxf333 low vigor. I grafted some susceptible varieties on callery but it will be years until I know how my tests turn out. In my lifetime I expect to leave behind some very useful information for the next generation unless something happens to cut my research short. Kansas has never grown many pears so the research is critical here. The way they are burning up top soil here due to erosion they will need the information sooner than they might know.


And yet out here it is obvious everywhere you go.

The hard science for “real” trees, paraphrased: “the life center of the tree is underground, everything above ground is sex and solar panels”.

Thus: stress below ground → stress above ground.

Observationally magnets, but because they are great hosts.

In your climate, regardless in mine.

Out here, Zinc chelate (e.g. Zinc lignosulfate) is used on some crops (e.g. table grapes) to control fungal attacks in coastal-influenced areas. In my experience it also has a positive influence as a summer spray on FB prone plants.


I am removing all apples and grafting my own Asian pear trees on ohfx97 rootstock. Hopefully this will build some resistance over the next few years. I will immediately discard of anything showing symptoms of FB.

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I agree Zinc is critical as in my opinion is boron and magnesium. Since these trace minerals are essential in very small quantities it’s a hard call.

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That’s why I have them in my fertilizer. But the mildew pressure here is high so a mid-summer spraying is also helpful to most plants – including the Citrus.


Excellent ingredients Richard I like the looks of that fertilizer.

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This double and triple spring that most of us are experiencing has
exacerbated the problem and prolonged FB season drastically. None of
my trees should be blooming now, but they are, and these rat tail blooms
are the cause of the prolonged FB season, because that’s where the disease
enters the tree. So every morning I go around and prune out all of these rat
tail blooms, so that the disease will stop on its own. It’s too late to spray
anything for this season.


Great advice Ray. I just finished doing it.


I don’t believe high humidity will cause the bacteria to enter the blossoms and cause the blossom blight phase of FB, but I have seen some models that suggested that humidity above 85% is the same as a “wetting event” like rain or dew.

I rely on the Cougarblight forecasting model which is connected to measurement devices in certain areas by Cornell. Lots of weather data from locations in major apple growing areas in NY, MI, PA, VA and some in NC go into the system. This model originated in Washington state, but I don’t see locations in the western part of the country. The same system uses weather data to make predictions about other diseases like scab. Part of the prediction is based on if you had FB in your neighborhood last year. The greater the amount of carry over FB bacteria from the previous year, the more likely you will experience it again this year.

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Regarding Zinc chelate: as you probably know, zinc can be used as a biocide. It

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To finish my thought…

Zinc is a biocide but much higher concentrations are needed than copper.


Research is pretty clear on what causes a fb outbreak. It’s mostly about the weather. Temperature but mostly water; rain, humidity, and dew. It is ever present but cankers that ooze in spring are especially bad.

Hail and insect punctures can be a factor but mostly on tender young foliage. However we have lots of hail and cicada in west Texas and I’ve only seen fb once in Alpine, the one yr we had a rainy wet spring. The cicada in Amarillo are every yr all summer. Their whining racket is enough to drive a guy crazy. They puncture the limbs every summer but zero fb.

There are models that predict fb based on weather. I think they even have sensors that detect water on the foliage.

It is highly variable and outbreaks can seemingly come out of no where. So I don’t discount anyone’s experience.

I was blown away the one yr it hit hard here after not seeing it in 45 yrs.

Here’s a quote from my link:

Fire blight bacteria overwinter in cankers on twigs, branches, or trunks of host trees. In spring when the weather is sufficiently warm and moist and trees resume growth, a small percentage of the cankers become active as bacteria multiply and ooze from branch or twig surfaces in a light tan liquid. Splashing rain or insects transmit the bacteria to nearby blossoms or succulent growing shoots. Once blossoms are contaminated with the bacteria, honey bees become efficient carriers of the pathogen.

Injuries on tender young leaves and shoots, caused by wind, hail, or insect punctures, are easily invaded by the fire blight bacteria. Such infections lead to shoot blight. Ideal conditions for infection, disease development, and spread of the pathogen are rainy or humid weather with daytime temperatures from 75° to 85°F, especially when night temperatures stay above 55°F.

Fire blight bacteria generally don’t move uniformly through the bark but invade healthy wood by moving in narrow paths up to 1 1⁄2 inches wide in the outer bark ahead of the main infection. These long, narrow infections can extend 2 to 3 feet beyond the edge of the main infection or canker. If you expose bark from an infected woody area, you will see that the diseased tissue closest to the main canker is brown. Farther out, the infection turns red and then appears as flecking. Just beyond the visible infection the tissue will look healthy.

Tree vigor has a major influence on the extent of fire blight damage. Once established, the distance the pathogen moves relates directly to the susceptibility of the tree and rate of tree growth. Vigorously growing shoots are the most severely affected; therefore, conditions such as high soil fertility and abundant soil moisture, which favor rapid shoot growth, increase the severity of damage to trees. In general, trees are more susceptible when young and suffer less damage as they age.


Fire blight development is influenced primarily by seasonal weather. When temperatures of 75° to 85°F are accompanied by intermittent rain or hail, conditions are ideal for disease development. The succulent tissue of rapidly growing trees is especially vulnerable; thus excess nitrogen fertilization and heavy pruning, which promote such growth, should be avoided. Trees shouldn’t be irrigated during bloom. Monitor trees regularly, and remove and destroy fire blight infections. (See Removing Diseased Wood.) If fire blight has been a problem in the past, apply blossom sprays. Sprays prevent new infections but won’t eliminate wood infections; these must be pruned out. In years when weather conditions are very conducive to fire blight development, it can be difficult if not impossible to control the disease.


I have learned the hard way that rooting from cuttings it’s much easier to get fire blight than with the grafting method. A lot of my cuttings of different varieties from 4 different sources are infected. Yet one of the Altoona, IA appears to be unaffected by blight.