I'd like to add my two cents to Tim Smith's excellent email of Jul 3.
First, the FB models, MaryBlyt and Cougar Blight, can appear to be
complicated, particularly MaryBlyt. To use Maryblyt correctly,
temperature data has to be fed in for every day from green tip on
through bloom. However, Cougar Blight is much simpler, and relies on
only four days of information to give you an estimate. Even
undergraduate students here at UMass can do it. And if you don't want
to run them yourself, usually someone, either private or university,
will run them for you or on a regional basis, and deliver the
information via email. This year, both FB models were off the charts
predicting very high risk of infection in MA and much of New England.
We put out an email warning in our newsletter Healthy Fruit, a couple
in fact, saying that this looked like an exceptionally nasty year.
We recommended treating with strep at bloom in orchards with any FB
history, or with particularly susceptible varieties or young trees. I
think that those growers who did that were reasonably happy, and that
where we have FB now, it is a case of one of the following:
a) no strep applied at bloom;
b) strep applied at full bloom, but not to late blossoms that came a
week or more later.
Of course, there were growers who didn't apply strep and didn't get
FB. They rolled the dice and won - this time. We don't know why that
happens. Vincent Phillion noted that in his part of the world, the
frozen north, FB is extremely sporadic. That's the nature of the
disease, and in my 25 plus years in MA, I've seen the same thing. But
there has been a trend towards increasingly widespread FB over that
time. This year is the worst I've ever seen, not necessarily in terms
of severity where it hits, but in terms of the number of orchards
hit. With time, I wouldn't be surprised to see our FB outbreaks look
more like those in PA and MD, while Quebec begins to look more like us.
There's a lot we still don't know about this disease, but we do have
a reasonably good understanding about whether and when to apply strep
at bloom. Unfortunately we can't predict shoot blight very well.
Shoot blight strep sprays, outside of hail or other trauma damage,
are not a good idea. In fact, they're a down right lousy idea. As Tim
noted, trying to control FB after bloom with strep doesn't work. In
fact, those sprays will increase the chances that strep won't work at
bloom, because the bacteria will develop resistance. Several
pathologists have noted that where resistance has arisen, it has been
in places where streptomycin was used regularly during the summer in
questionable attempts to try to control shoot blight. Summer cover
sprays of streptomycin aren't the answer to shoot blight.
If we're going to keep strep a useful product, it needs to be used
only at bloom or during trauma events, and only during those times
when the models say there's a risk of FB. Otherwise, it'll quickly
become useless. The odds that a new antibiotic will be approved for
general use in orchard sprays are about the same as me winning
MegaBucks.
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