May 4 fire blight prediction

Hi Fruit Growers,

Dave Rosenberger, retired plant pathologist at Cornell’s Hudson Valley Lab, says the predictions for fire blight are even worse this spring than last year. We can track the predicted threat of fire blight by looking at models on Orchard Radar. You can see the Orchard Radar predictions at the URI Apple IPM site at on the left side of the page.

Click on Greenville or Newport County, whichever site is closer to you. Then click on fire blight then click on CougarBlight. According to this model, a fire blight infection is predicted for May 11th in Greenville area.

Fire blight is a problem when flowers are open. And this warm weather before bloom means flowers will be at risk once they open – assuming weather predictions are accurate. I hope everyone has strep in their spray sheds.

Wet weather is needed for fire blight to infect flowers, but dew can be enough to cause an infection. Strep should be sprayed right before a predicted infection or within 24 hours after an infection. It’s recommended to add Regulaid to the first strep application. I say first strep application because it may take 2 or even 3 applications to protect from fire blight.

Keep checking the models – and I will too.

Below is a message from Dave Rosenberger and below that is Kerik Cox’s article that appeared in today’s Scaffolds newsletter from Cornell.

From Dave Rosenberger:

Attached are MaryBlyt (MB) runs using Accuweather forecasts for the next week and NEWA data from HVL for the dates up to yesterday.  The forecast is pretty dire as it relates to fire blight.  Last year was as bad a year for blossom blight as I have ever seen in the Hudson Valley, but this year will be far worse if the weather predictions are correct.  Last year we had 5 days during peak bloom that had a MaryBlyt EIP>100 (meaning enough heat units to allow blossom infections if wetting occurred). The mean EIP for those five days was 175.  Using today’s forecast, we may well end up with 11 consecutive days during bloom with EIP>100 this year, and the projected mean EIP for those days is 193.  In the absence of any strep sprays, the highest EIP predicted is 332 on Sunday, May 10th.

The first graph below shows what will happen if no strep sprays are applied and if it rains as predicted sometime tomorrow and again next Sun-Mon-Tues.  The only reason that infection periods are not indicated on May 7-9 is that I did not enter any wetting for those days.  The second graph below shows what could be expected if one had open flowers today and then sprayed strep on Wed morning, and again on Saturday and the following Monday.  You can see that the model suggests that even with 3 sprays, we would not be fully protected, but I think that those three spray timings may be good enough if the weather develops as currently predicted. (I don’t think that the model gives us credit for 24 hr of kickback on strep sprays.)  Even though we theoretically could get infections with just the heat units from today alone, the risk is still relatively low because of the small number of open blossoms (at least here at HVL) and the fact that bees have not yet had much time to move things around.  A spray on Wed morning will cover any rains that occur on Tuesday, but in some locations growers may want to cover up on Tuesday after any showers have moved through.  By suggesting sprays on both Saturday and Monday, I am attempting two things:  first, those timings will sandwich the potential rain event on Sunday May 10th, and if the weather forecast holds, that has the potential to be the biggest blight infection event that I have seen during my career in the Hudson Valley.  Having full cover sprays on both sides of it will help to cut risks, and you will need multiple sprays anyway to cover all of the heat units that will be occurring next Sat-Tues.  However, if there is no rain today or tomorrow, it will still be important to get strep applied in high-risk blocks on Tues, Wed, or Thurs of this week because failure to do so will just allow too much inoculum to build up before any strep is applied.  Below the attached graphs is part of a Scaffolds article that will appear later today in which I explain the rationale for spraying strep even when there is not wetting.

Hopefully the weather forecast will be wrong and cooler temps will prevail as the week progresses.  If not, then I expect the worst. Remember that as EIP values increase, we tend to see blight infections in older trees and in cultivars that under moderate conditions might be considered almost immune to blight.  For example, when the EIP in Michigan passed 400 several years ago, even Red Delicious trees collapsed from blight.  If our EIP passes 300, we will see at least as much blight in mature trees as last year, and probably considerably more because we probably have more inoculum this year.  So please, convince your grower communities that they should not mess around and just hope for the best. They need to plan to get strep applied, probably multiple times over the next week. (And by the way, I don’t get any commission on how much strep is sold 🙂

Following is part of what will show up in Scaffolds later today:

Guidelines for Managing Fire Blight in 2015
Kerik Cox, PPPMB, Geneva, NY
Debbie Breth, LOFT, Albion, NY
Juliet Carroll, NYSIPM, Geneva, NY
Dave Rosenberger, PPPMB, Highland, NY

Last season fire blight was unusually severe throughout NY and the rest of the Northeastern United States. Moreover, there were many odd tree decline scenarios in 2014, such a case in Vermont where fire blight ooze was found at silvertip along with other situations where fire blight was associated with stem borers, winter injury, and herbicide damage in scenarios that were impossible to tease apart. Impacts of last season’s damage are still being felt in the form of dead or dying trees in the spring of 2015. These situations cause considerable trepidation as apples in eastern NY and southern New England move into bloom this week, a week during which hot weather, oozing cankers from last year, and the predicted rains could create another year of severe fire blight if flowers are not protected from infection.

Last year, some growers in the Hudson Valley and New England applied streptomycin sprays only to young plantings and high-risk cultivars on the assumption that older orchards of cultivars such as McIntosh, Golden Delicious, and Empire were not very susceptible and therefore did not warrant protection. Furthermore, the strep sprays were applied only after a string of warm days that allowed an accumulation of high epiphytic infection potential (EIP) because we assumed that sprays were not needed so long as there was no rain, dew, or other source of moisture to move bacteria from the stigmas to the infections sites at the bases of the flowers. On many of those farms, the strep sprays were very effective for protecting trees to which it was applied, but older trees that had not been protected developed significant amounts of fire blight. As the season progressed, the blight sometimes moved from these older infected trees back into young trees where shoot blight infections caused additional damage. In retrospect, it appears that delaying the first spray until rain or wetting was predicted allowed too much time for the bacteria to be disseminated in high numbers to older blocks that generally might have escaped infection if weather favorable for blight had been of a shorter duration.

In the Hudson Valley, this year is shaping up to be a repeat of last year:  Weather forecasts are indicating at least a week of very warm weather (highs in the upper 70’s and low 80’s) as apples are coming into bloom. Some areas may get rain on Tuesday, but other areas may not have any rain or may not yet have trees in bloom on Tuesday. After that, no rain is forecast until next Sunday.  If no strep is applied until the end of the week, that would once again allow plenty of time for wide dissemination of fire blight bacteria prior to the first strep application.

To prevent a recurrence of last year’s problems, we suggest two specific strategies that should be implemented this year.  First, highly susceptible blocks should be sprayed with strep as soon as the EIP exceeds 100 even if no rain or dew has occurred. (This would be Wednesday or Thursday in the lower Hudson Valley.) This approach will eliminate inoculum in the middle of the bloom period rather than allowing it to multiply on flower stigmas and be disseminated without restraint as will occur if strep applications are delayed until late in the week. Second, when rain finally is predicted after multiple days of warm weather (70 to 80°F.), ALL orchards should be treated with strep within 24 hours prior to the rain rather than focusing treatment only on blocks considered “highly susceptible” because even older trees of less susceptible cultivars will get blight if temperatures remain high for many days during bloom. Thus, we are suggesting a pre-emptive strep application on high-risk blocks after EIP exceeds 100 followed by the usual strep application timing ahead of any subsequent rain(s), with the latter applied to ALL orchards. Where orchards cannot all be covered ahead of rains, strep can be applied within 24 hours after the rain.