This was my thought too when I purchased pear scions for the first time this year. I figure if I’m going to invest in the fruit I might as well try anything that could work. If a variety only lives a few years but makes some fruit, I can plant those seeds.
I also haven’t seen any obvious cases of fireblight around me (though I assume the disease is here) so I am willing to test the boundaries a bit. Same with rust, even though there are junipers everywhere.
Warren, Seckel, Olton Broussard, Hosui, Shinko, MoonGlow, Clark, and Plumblee were all hit hard by fire blight last season. The pressure here is so intense that I am close to replacing all my pome and stone fruits.
lol! I’m almost the exact opposite. I have so much fireblight I assume everything is going to get it.
My advice wait out the fireblight and spray with antibiotics if necessary
I made a list of Pear trees from Clarkinks list and from nursery websites of Fire Blight resistant pears. I did not include pears listed as moderate or with some fire blight resistance. I tried to capture if they were self-pollinating and the bloom group. This may help folks (or maybe not).
Comice and Spalding don’t belong on that list. Both are susceptible to fireblight. You have Duchess d’Angouleme listed twice but should only be one time. Clark spelled it wrong in the first post. Bell is missing from the list but should definitely be there. Starking Delicious and Maxine are the same pear. I could comment about several others, but will leave that for Clark and others to do. You might look at Grandpa’s Orchard for some other info.
This isn’t meant to come off as an authoritative opinion, bur rather a thought exercise based on my current understanding of fireblight and reading about different strains. I expect others will have more knowledge to contribute on the subject but here are my thoughts anyway.
It is my understanding that, for the most part, there is no single gene resistance for fireblight. The only possible known exception being for the crabapple M. x robusta No. 5, and in that case the resistance has been matched.
So by and large any resistance to fireblight, particularly in pears, is a quantitative resistance or what is sometimes referred to as horizontal resistance, and the effectiveness of horizontal resistance varies greatly by geographic area.
Also, fireblight is said to have low genetic diversity with most of the variations between strains being Single Nucleotide Polymorphisms (SNP’s), with the number of SNP’s being attributed more to the geographic location rather than the host of the strain.
So, it seems to me that a list of fireblight resistant pears is really only useful if it’s broken down by the general location for which growers have shown them to have good resistance. That actually shouldn’t be that difficult to accomplish over time using a voting system of verified growers on the forum. Maybe the votes would need to be weighted some based on a few different criteria, but still a relatively straight forward approach.
Lasty, once you have good geographic lists, I would think that it wouldn’t be all that difficult to come up with new varieties that are adapted to your new local strains by planting seeds from the most resistant varieties for your specific location. The thought being that since fireblight isn’t very genetically diverse you should be able to decently increase the horizontal resistance in a single generation since the current resistance, even though occasionally inadequate for some new strains, is still based on long standing horizontal resistance. Time to fruit being worst part of that process.
I would agree on most of this but it is missing some key context. Fireblight spreads readily in the environment where what affects Clark this year might hit me in 2 or 3 years. Also, fireblight tends to have a huge spring infection event where a single strain affects a geographic area. The next year, a different strain may affect the same area.
I agree that fireblight resistance is from horizontal mechanisms. This just means that there are several individual genes/traits that added together give a variety with good resistance. I don’t think there is an R gene complex that contributes to fireblight tolerance, but can’t rule it out. R genes can be thought of as a group of genes that act like a lock and key that affect resistance to a single disease organism where some of the R genes are compromised but others are still effective. Potato late blight resistance is a classic example of an R gene complex where individual R genes can be stacked into a single variety giving a type of polygenic resistance. Different strains of late blight can infect some potato varieties but not others based on which R genes are in the different varieties.
To get to the point, fireblight is not regional therefore trying to figure out which varieties are resistant in a given region won’t work. What will work is to figure out which varieties show high resistance in a large number of regions against a large number of strains of fireblight. Those will be the varieties that can be grown with high levels of success just about anywhere.
One of the most effective ways to limit disease problems with plants is to grow several different varieties each with slightly different genes for fireblight resistance. That way, a single strain can’t decimate an orchard.
There are also cultural contributions to fireblight resistance. For example, have you noticed that when trees are heavily fertilized they tend to be more susceptible?
I’m impressed that you made a list and began working on your plan.
Harrow delight has a little resistant
Atlantic queen is not resistant
Beurre giffard is not resistant
Chapin is not resistant
Comice is not resistant
Johantorp is not resistant
Vermont Beauty is not resistant
Summercrisp is not resistant
Baby shipova and crosses are not resistant
Spalding has little resistant
This is what fusion power mentioned
To add onto what @Fusion_power is saying, since fireblight partly lives in the air, clusters of the bacteria can float in the wind and land in a new location with a suitable host, where it then establishes itself and can spread. Sort of like northern fowl mites travelling on birds and landing in new locations.
This is why the notion of 'geographic adaptation’ is a bit fuzzy for FB. New strains can pop in at anytime from wherever the wind came from. I do think there is some truth in the idea - a more ideal climate/soil for a particular pear better supports its immune system.
This part is the most important. Can’t really have field adaptation without field adaptation.
Thank you so much for the list in particular where you can buy the trees. That has been a major obstacle for me where to buy the trees once I decide on a variety to try .
Remember fireblight is a bacteria. Bleach, alcohol, vinegar , copper, and antibiotics all kill bacteria. Some of those like vinegar are a mild herbicide for plants also. I’m not suggesting you use them all for everything. I am saying you can clean pruners between cuts. You can spray trees with copper or antibiotics. Do.not feel fireblight is a problem without a solution. The solution in some areas may take a multifaceted approach of planting resistant pears, spraying in spring and fall with copper, cleaning tools etc. The first step is understanding the disease. This is an example of an antibiotic Streptomycin Sulfate Powder
Everything used should be labeled for Erwinia amylovora
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Fire blight, caused by the bacterium Erwinia amylovora, is one of the most destructive diseases in apple and pear production. Fire blight can infect other members of the rose family including quince, juneberry, hawthorne, mountain-ash, and Pyracantha.
Causal agent of fire blight
Symptoms and signs of fire blight
Disease cycle and epidemiology of fire blight
Management of fire blight
With the exception of China and Australia, fire blight occurs worldwide in all regions where apples and pears are grown. Under conditions favoring disease, fire blight can infect, blight, and kill trees across large acreages over the course of only a few weeks. Disease outbreaks are often sporadic and the disease is difficult to manage. Estimated economic losses in the U.S. exceed $100 million annually.
Erwinia amylovora, is a Gram-negative bacterium in the Enterobacteriaceae. It grows most efficiently in warm, moist conditions, preferentially colonizing flower stigmas. The bacteria cannot penetrate cells directly and require natural openings or damaged tissue to enter the host. Once inside the plant, E. amylovora can move systemically within the plant via the vascular tissues, ahead of symptom expression by the infected plant. Some differences in host range and aggressiveness have been described between strains. Erwinia amylovora can share genes on small DNA molecules called plasmids, which is one way antibiotic resistance can spread through bacterial Populations.
Erwinia amylovora can infect flowers, shoots, fruits, and woody tissues. Blighted tissues initially have a water soaked appearance, then wilt and turn black or brown within 1-3 weeks. All infected tissues may produce droplets of bacterial ooze, pale yellow to dark amber in color (Fig. 1 and 2), which is attractive to insects and serves as inoculum for disease transmission. Four types of infections may occur, with slightly different symptoms.
Open blossoms are colonized via the flowers’ stigmas and from there they gain entry via natural openings in the nectaries. Infected flowers and peduncles wilt, shrivel and darken. Infected fruitlets wither, turning black or brown. The entire flower cluster may shrivel and die but remain firmly attached to the tree (Fig. 3).
Shoot tips wilt, turn black or brown, and bend down, forming the characteristic symptom called a shepherds crook (Fig. 4). Infected leaves often turn black or purplish-brown along the mid-vein, as bacteria colonize the vascular tissue and move into the shoot. Young shoots are most susceptible and symptoms often stop at older, woody tissue. Apple leaves killed by fire blight turn dark orange-brown, whereas pear leaves will turn black.
As bacteria move into the tree from infected shoots, infected woody tissues may form cankers (Fig. 5). Shoots infected by bacteria moving into them from cankers, often appear distinctly orange-brown. Cankers may girdle the trunk, leading to tree collapse and death. The bacteria in overwintered cankers become active in the spring and may move systemically to adjacent, new growth. Bacterial ooze may form on the edges of cankers in spring.
Bacteria can move systemically through vascular tissue from blighted blossoms or shoots to the rootstock, where a local canker forms. Sunken purple or orange cankers on infected rootstocks may girdle the trunk, leading to tree collapse and death.
Figure 1. Wilting, blackened shoot tip with droplets of bacterial ooze and necrosis (blackening) along the leaf mid-veins.
Figure 2. Gala fruit infected with E. amylovora producing droplets of bacterial ooze.
Figure 3. Wilting flower cluster and spur leaves infected with E. amylovora; typical blossom blight symptoms.
Figure 4. Blighted shoot infected with E. amylovora; typical shoot blight symptoms.
Figure 5. Canker producing bacterial ooze in early spring; typical canker blight symptoms.
Fire blight bacteria require living host tissue to survive, but may persist on other materials for short periods and in pruned infected branches that are kept moist. Bacterial growth occurs over a wide range of temperatures, from 39°F to 99°F (4°C to 37°C), with an optimal range of 70°F to 77°F (21°C to 25°C). Blossom or shoot blight symptoms occur approximately 90 to 100 degree days base 55°F after infection or within about one to three weeks. The bacteria overwinter at the margins of cankers. In spring, cankers produce ooze when temperatures rise and tree growth begins. Insects, wind, and rain can carry bacterial ooze from cankers to open flowers. Flies and bees visiting flowers can spread fire blight bacteria to other open flowers. On flowers, the bacteria preferentially colonize the stigma. Bacteria get washed into the floral cup during rain, heavy dew, or spray applications where they enter the host via openings in the nectary glands, leading to blossom blight infections (Fig. 3). The requirements for blossom blight infection include open blossoms, sufficient heat for bacterial population growth, a wetting event, and continued heat for infection.
Infected blossoms and other plant tissues produce high levels of bacteria that may spread by wind, rain, and possibly insects, for shoot blight infections (Figs. 1 and 4) later in the season. Shoot blight is favored by traumatic events that cause mechanical injury, such as strong winds, thunderstorms, hail, or piercing-sucking insects (e.g. leafhoppers and plant bugs). The bacteria enter through wounds and move systemically through the vascular tissue. Bacteria may travel to the rootstock, leading to rootstock blight and tree death. When trees remain alive and successfully compartmentalize the infection, cankers form on scaffold branches, trunks, and rootstocks that overwinter to complete the disease cycle.
Figure 6. Disease cycle of Erwinia amylovora, causal bacteria of fire blight.
Cankers ooze in the spring as the weather warms and lands on open flowers.
Bacteria multiplying on the stigma infect through floral nectaries. This is the primary infection. (A)
Blossoms blight as bacteria invades. Secondary infection may occur due to insects and wind dispersing bacteria to actively growing tissues. (B)
Bacteria travel to active growing shoot tips and developing fruit, which may ooze or blight.
Bacterial invasion ends at terminal bud set, but entire shoots may blight;
Bacteria overwinters in cankers formed on shoots and trunks in the fall.
A successful management program includes an integrated approach, including planting resistant varieties and rootstocks, avoiding excess nitrogen fertilization, controlling shoot vigor, reducing inoculum and its spread in the orchard, environmental monitoring for disease risk, and judicious application of crop protectants. Young trees and dwarf trees grown in high-density systems may be less resilient because they have less woody tissue, may be less capable of walling off infection, and infection will spread more readily into the trunk or rootstock to kill the tree.
Choose resistant cultivars such as Jonafree, Prima, Priscilla, RedFree, Empire, Delicious, Honeycrisp, Jonagold, Liberty, McIntosh, and Northern Spy whenever possible. Avoid highly susceptible cultivars such as Fuji, Gala, Gingergold, Honeycrisp, Idared, Jonathan, Lady Apple, Paulared, Rome, and SweeTango. Use resistant rootstocks, such as the Geneva series, and avoid susceptible rootstocks such as M.9 and M.26.
Vigorous shoot growth is highly susceptible to fire blight. Manage tree vigor by maintaining a balanced nutrient program without excess nitrogen and avoid excessive winter pruning. The plant growth regulator prohexadione-calcium can control shoot growth and can prove highly effective against fire blight infection, but may compromise shoot growth.
Reducing overwintering inoculum is critical for managing fire blight. Remove cankers during dormant pruning. Trees with trunk or rootstock cankers should be removed completely. Copper products applied at late dormant or between green tip and bloom can reduce inoculum on the surface of the tree.
During spring and summer, prune shoot blight strikes at least 8 to 12 inches below visible symptoms as soon as possible after they have been observed. Always prune during dry weather. Sterilize pruning equipment with 10% bleach between cuts to help prevent spread of the disease; oil pruning equipment after using bleach to prevent corrosion. Avoid dragging infected prunings through the orchard and rubbing them against healthy trees. Destroy pruned material by burning or leave them to dry out completely and then flail mow.
Precise timing of blossom sprays is critical to blossom blight management. The disease forecast models, MaryBlyt 7.1 and Cougarblight 2010, predict fire blight risk and application timing. Consult the NEWA disease forecasting system for output from these models. The appearance of shoot blight symptoms may also be predicted using disease forecasts and can aid in determining when to scout to prune strikes.
In most commercial orchards with a history of fire blight or susceptible cultivars, chemical control is necessary. Copper products may be applied after pink, but only if fruit russett can be tolerated in the market. Antibiotics will effectively protect open flowers from blossom blight. Several new products, including biopesticides, have shown efficacy against fire blight by colonizing blossoms, outcompeting or killing the pathogen, or activating the plant’s natural defenses. To protect against shoot blight, antibiotics should be applied only if a trauma event occurs, in order to minimize the risk of antibiotic resistance developing in the bacteria.
Prudent antibiotic resistance management practices include limiting the number of applications during bloom to three or less, alternating sprays with other materials, and avoiding their use during summer against shoot blight. Streptomycin acts by killing bacterial cells and is effective if applied within 24 hours of infection. Streptomycin resistance in E. amylovora populations exists in nearly all major apple production regions in North America. Therefore, use management tactics to reduce the risk of streptomycin resistance. Two other antibiotics, kasumin and oxytetracycline, and other products labeled for fire blight provide options for rotating use with streptomycin for resistance management. Consult the Cornell Pest Management Guidelines for Commercial Tree Fruit Production, updated yearly, for detailed information on chemical management.
Anna Wallis
Plant Pathology and Plant-Microbe Biology Section, Cornell University
Juliet Carroll
Cornell Integrated Pest Management Program, Cornell University
Kerik Cox
Plant Pathology and Plant-Microbe Biology Section, Cornell University
Last updated: 2024
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Bell sounds like an exciting variety. We started prepping for new pear trees today. I have really hard red clay soil, so we dig really big holes and amend with manure. My son picked up a pickup load today. Even though the site has tall trees on 3 sides I think it will get enough sunlight. Here is a pic of the site:
Is the soil as red as in the picture? I haven’t seen soil that dark red before. Light red, sure.
Yes, it is that dark red, it will lighten up some if it is totally dry. My understanding the red is from high iron content, there are old iron mines and ironworks in the general area. Not sure if that is accurate.
That was my understanding as well, iron oxides (essentially rust, from iron being weathered in the parent rock). I used to live in a place with a light red, sticky clay soil.
I use 3% hydrogen peroxide to clean my pruning and grafting tools.
Yes, I thought I observed the fertilizer dependency on apples. It was really bad one spring following urea spray in the fall and early spring fertilizer application. I figured that the high nitrogen stored in the twigs and rampant new growth was letting the bacteria replicate strongly. Could also be that plant defenses are down regulated at the same time, as for example tannin levels in apples go down with fertilization. I switched then to fertilization after bloom and had much less issues. The other thing I am doing is to not thin fruitletts out till a few weeks after bloom.
Who sells real seckel trees?
