May 15, 2015
Specialists forecast the fire blight season for 2015

Fruit Growers News asked specialists from several regions to discuss the prospects for fire blight in the coming season. Their observations, made in the last few days, are below.

West

Timothy Smith, Washington State University: It rained across most of Washington orchard areas last night and today, and the temperatures leading up to this rainy period were in the mid-70s, and as high as 80˚ F during the four to five days leading up to the rain. The fire blight model (CougarBlight 2010) indicated a high or extreme risk of blossom infection, especially in blocks that have a history of fire blight in the neighborhood. The most vulnerable crops are pears; apples likely are at lower than normal risk due to fewer secondary blossoms.

There were strong infection periods last season, which may have increased the number of carry-over live cankers in some regions this year. The blight problems seemed to be more common in the northern half of the growing areas last year, which leads to a higher than normal potential in the north for new infections this season.

Some orchards in the southern half of the production areas struggled with blight in apples in 2010, 2011, 2012 and 2013, but seem to have brought their fire blight problems to much lower levels in 2014. They have been more proactive in their control methods lately, due to a healthy respect for the potential of this disease.

The apples and pears blossomed long ago in all regions of the state (everything is 10-14 days earlier than usual this year), but the pear trees have a higher than usual number of secondary blossoms out at this time. These secondary blossoms have had weather conditions this past week that made infection possible today. Most growers don’t protect their secondary blossoms, and those are most often where blight occurs. Secondary blossom infection can cause serious damage if left uncut, but the damage potential is far less severe than what can occur from an infection period during primary bloom.

In our experience, this all means that somebody is going to have blight this season. Who and where is the real question. I suspect that most growers have a good understanding of all the infection factors that lead to blight, and have already responded with control measures in high-risk situations.

Ken Johnson, Oregon State University: I have not heard much about fire blight this year, but it is early. The spring (in Oregon) was very early, with bloom of pears (and to some extent apples) happening in cooler weather.

Generally, early springs have less blight than late springs (because the days are cooler). That said, I’m sure there will be some cases of blight, but probably not a lot.

While blight stories are not so common, there is an above-average amount of secondary bloom this year (termed rattail bloom). These are straggly flowers that open in May and June, well after the primary bloom. Because they open late and in warm weather, they are at much greater risk of fire blight infection.

Because of lower density, infected rattail flowers generally are not a disaster situation, but a nuisance that requires time to cut it out. (Rattail infections also help to perpetuate the disease from season to season.)

There is enough rattail this year that sprays are going on to protect them from infection. Usually there is not enough rattail to make the sprays worthwhile.

Rachel Elkins, University of California: In general, this has been a very bad blight year (in California) because bloom was very early and the “disease triangle” lined up perfectly: early bloom (host susceptibility), ideal weather (warm and some key moisture periods) and inoculum (which in California is a given). Cultivars that are not generally susceptible bloomed early and were out during susceptible periods. Full bloom dates were in mid-March rather than April (earliest in history). Bloom was extended due to the lack of chilling, and so the treatment season is long.

There were a couple of frost events that created wounds, and some hail that enabled blight to get into shoots and leaves, as well as on fruit (but this is uncommon). I have never seen so many ornamental pears hit with blight; they are riddled. They bloom early. Also, we don’t generally see Comice and Seckel, but they bloomed early and were hit this year.

For conventional growers with access to antibiotics, problems were likely due to missing an infection period (early or late) or spraying at too-infrequent intervals, because when flowers continually open it is often necessary to spray every other day, since there is only a three- to four-day efficacy period for antibiotics and only strep is partially systemic. Organic growers lost antibiotics this year, and this is the first year we are assessing commercial applications of biological and acceptable copper products.

As for copper, this was a real test year of its efficacy, and it is my observation that copper must be applied at the higher rates – and even then does not perform as well as antibiotics in this very high-pressure blight year.

The most important thing growers can do is practice sanitation, i.e. cut out the blight. Apogee is not registered in pears and research is needed on controlling shoot blight; right now there is no good option for this in pear.

East

David Rosenberger, Cornell University: In (New York’s) Hudson Valley, we had what may have been our warmest bloom period on record. Because of the heat, both the MaryBlyt and CougarBlight models for predicting blossom infections indicated that blossoms could have been susceptible to infection throughout the entire 10- to 12-day bloom period. However, water is required to move the fire blight bacteria from the flower stigmas to the infection sites at the base of each flower, and our bloom period was relatively dry.

No one is really certain how much infection may have occurred as the result of dew periods and several very short and scattered rain events that occurred during bloom. Most growers applied multiple streptomycin sprays (in many cases, three applications) to young orchards and to susceptible cultivars, but I’m not certain how many growers covered older trees. The amount of streptomycin applied was much, much higher than in previous years, because many growers had a bit more fire blight last year than they would have liked and therefore were very concerned about carryover inoculum.

Winners and losers in the fire blight roulette that occurred during bloom will not learn their fates for several more weeks. Although my Extension experience with fire blight covers more than 35 years, I really have no idea if those who sprayed three times will be upset because neighbors who never sprayed also had no fire blight (due to dry conditions), or if those who chose not to spray older trees will be cursing their luck when fire blight shows up in unexpected places.

George Sundin, Michigan State University: The potential for fire blight will be the highest in eastern and southwest Michigan and the Fruit Ridge. These were the areas that had the warmest temperatures and open bloom, which could have allowed fire blight bacteria to build up rapidly on flowers. Also, rain events occurring in the last few days would have triggered infection.

With the very cool, cold weather now, any new fire blight risk will be low for the next several days, and in regions like northwest Michigan that did not have much bloom open, their risk is pretty low right now.

Even though temperatures are low now, the high-risk regions still may get some significant infection. This is because flowers may have been infected and symptoms won’t show for a while because it has gotten colder. We basically have to wait and see what happened. I think most growers have applied at least two fire blight sprays, and so I am hoping for good control.

The potential for fire blight is great in the three highest-risk regions, which had the most conducive fire blight weather. If significant blossom blight symptoms develop, it will be a long, bad season, with shoot blight and disease spread throughout the summer. However, if growers kept the blossom infection under control, this year will revert to a “normal” fire blight year, where we still have to be on alert for disease but will not be dealing with a major epidemic.

Kari Peter, Penn State University: It’s still too early to tell. Since fire blight was bad in Pennsylvania last year, we can assume that there was the potential for a lot of bacteria to be present during bloom. The weather warmed up very fast, which would allow any bacteria in the flower to replicate like crazy and be fair game for causing infection, however, our bloom was pretty short in Pennsylvania and Maryland, and that may work in our favor. But dew was present just about every day during bloom, and that wouldn’t have worked in our favor. Time will only tell.

Chris Duyvelshoff, Perennia: Nova Scotia is still dealing with the cleanup and recovery from the 2014 fire blight epidemic. Growers are trying to remove as much overwintering canker as possible while pruning, and a lot of dormant copper has been used at bud break. We are still two to three weeks away from bloom, so it’s hard to say what the potential weather during the bloom period will be. There is a huge amount of potential inoculum in orchards due to last year’s infections. Growers are going to be treating most everything with streptomycin according to the Maryblyt model, and Apogee will be used extensively as well.

It’s really too early to say what our outcome might be yet. There is a huge risk due to last year’s infections, however growers are planning to use aggressive fire blight management this year. If we get a quick bloom period with relatively cool temperatures and dry weather, we should be OK. A warm, wet bloom period will be the worst outcome for Nova Scotia, and then it will all depend on correct application of streptomycin to control blossom blight.

The potential is bad, however growers are prepared and weather during bloom will likely be the ultimate tell. If bloom is OK and we don’t get any summer storms like last year, Nova Scotia should be in a lot better shape. There’s no reason to assume a disaster yet in 2015.

Phillip Brannen, University of Georgia: In (Georgia’s) commercial orchards, it has been minimal to date. I think we had more than sufficient moisture, but temperatures may have been too cool for optimal infections.




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