Why is the USDA Apple/Pear Fireblight Data so wonky, and what's the go-to source for apple/pear Fireblight information?

What’s the most reliable and complete source for Apple/Pear fireblight data?

I was picking out some new fruit trees, and referencing a copy of the USDA apple fireblight database that I downloaded a few years back. I have it in a spreadsheet alongside the Cornell disease database, and there are dramatic differences in the findings.

Take Arkansas Black, for example.

Cornell says Moderately Resistant, supported by 5 universities.
USDA says Very Susceptible - very heavy rating.

There are a lot like this. So, what gives? I’m inclined to disregard the USDA data.



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Because it varies by region. Apples are hardly touched by it here but fireblight prone Pears on OF rootstock can take a real beating. The same apples can be torched in some locations back east.

Are you saying that a cultivar’s resistance to fireblight changes by location, or disease pressure/type/exposure changes by location?

Both, Absolutely.

Which one?

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What would be the purpose of gathering and reporting the data if it was only valid in the location where gathered? I can understand different locations have different pressures, possible strains of fireblight, and exposure to fireblight.

The USDA has not paid people enough to study situations outside their repositories and test sites. With apples, many east coast repository staff still believe that apples have chill requirements.

The problem with resistance is the same problem we see in viruses. Mutation. It is why many southern states are on 3 or 4th generation super resistant pine trees. Get them in the feild and a few years later, a new race of disease cracks the resistance.

Example, Elstar/Ecolette were at least intermediate fireblight resistant on M.111. Important for organic growers. They are no longer so good against some strains of fireblight now.

Hood Pear has been a champion against FB for decades here in San Diego county.


No expert, but I found good local info looking to my nearest state college. WSU has lots of info duel reported for eastern vs western WA and their comparative differences.


This summer the semi-annual Intl. Symposium on Plant Nutrition of Fruit Crops will be held in Wenatchee, WA. The convener is Lee Kalcsits, WSU-TFREC.

Thanks. Agreed that there may be some variation or mutation. That said, are you suggesting that if one goes to a site, such as Cummins Nursery and finds a tree labeled as ‘fireblight susceptible’ or ‘fireblight resistant’, that the information is not useful; that is, it does not not generally suggest if a tree is able to fight a fireblight attack for most or many strains of the bacteria?

I think there must be some scientific merit, else there would not be all these universities testing and reporting data. Understood it may not be accurate for all locations and conditions, but maybe a broader indicator of how a tree will respond?

I stumbled across a journal article that provides some insight to the USDA data and how it was collected:

" The United States Department of Agriculture (USDA) Malus collection in Geneva, NY is home to over 6000 apple accessions and 48 species and hybrids from around the world. During the 2020 growing season, a naturally occurring severe outbreak of E. amylovora swept through the USDA apple collection, offering a unique opportunity to evaluate the germplasm for fire blight susceptibility and resistance. Although observations of fire blight in the collection were documented from 1990–2000 incidences of naturally occurring shoot blight [30], the data were not systematically collected across a large number of accessions under comparable conditions."

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I would hope what the descriptors say is true. All the way through the spectrum of various Ag interests. I recall reading one report that a particular tree was very scab resistant except for race 5. Which probably is a new player.

They should present that case. But realities might preclude it. Say if the Nursery never got the bulletin/report for example.

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Alright, so what does it mean about the data set of Cornell Compiled vs USDA, for instance, were there are a significant number of entries were USDA says highly susceptible to FB, and Cornell Compiled literature and vendors are saying not? That is why I was originally suggesting that perhaps the USDA data has to be disregarded.

I think the fundamental problem is that we don’t know the methodologies used, and so it could be that USDA just took notes over a decade or that they did some sort of lab testing where they checked how a cultivar’s cells responded to a wide spectrum of the bacteria. I guess I lean towards trusting the large vendors; if they sell a tree to a high-fireblight area, which is marketed as fireblight resistant… they’re likely to get feedback if a lot of those trees going to that area get wiped out or severe infections.

I guess I’ll just follow my gut and maybe be right and maybe learn a lesson the hard way!

You bring up some good points.

You might also ask here for reports of fireblight resistant varieties. For apples, a couple of pretty good lists have been posted recently. We have a thread on highly fireblight resistant pears. Search for ‘fire blight resistant pear’.

Your point is fair. But I do not completely trust USDA-GRIN data as the last word. I tend to look at pooled grower experience more then everything else. Like Orange Pippin. Like I said; I find GRIN-GLOBAL data newer, more user friendly compared to USDA-GRIN.

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There is high fireblight pressure here, residual in some natives and frequently planted ornamental pear and pyracantha.

Pear trees without high fireblight resistance are toasted. Apples rarely show more than tip burn – including cultivars hard-hit in the 2020 Geneva event.

I don’t think I know enough to know what I’m missing :slight_smile: I just stumbled on it and extracted the data to a spreadsheet.

Do you have a link hand to the USDA-GRIN?

Yeah, Orange Pippin and Cummins were two that I was cross referencing, as well. At first, I thought the data from Cummins was just matching Cornell’s database, but I did find some cases where they did not. OP seems to have a slightly different take on a number of them, so I’m guessing their data is coming from somewhere else.

It’s the same database. What urls are you using to access each?