Apple Pest Report:  Tuesday, July 26, 2005
Vol. 13 No. 8

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    Given the spring weather, the scab situation is remarkably good this summer.  Out of 36 separate orchard blocks checked by UMCE-Pom Soc. Co-op scout Laura Miller over the previous two weeks, five were at or above the tentative threshold of 5 scabby leaves per 100 shoots or fruit clusters.  (Each shoot or cluster includes about 15 leaves, so the total sample per orchard is about 1,500 leaves.)  And most of those five blocks were just at or over the 5 leaf threshold (scabby leaf counts in those blocks were 5,6,7,10 and 18).

    There is one block in the scout route with a much higher high scab level that was not checked because of REI (probably due to captan applied to suppress scab!).  That exception shows that the low scab level this summer is not due to absence of infection pressure, but is the result of successful grower effort.

    As of July 8, even orchards as far north as Old Town had enough time to show second generation lesions from all of this spring's primary scab infection periods.  So there should not be too many surprise encounters with scab popping up from now until mid-September at the earliest, and hopefully not at all. 

    With trees at or past terminal bud set, scab is denied tender young foliage to spread new infections and fruit become more resistant to infection as the summer progresses.  With big trees the risk remains for unnoticed scab in the high top center of the tree raining down onto leaves and fruit below.  Still, for growers with good scab control up to this point, fungicide decisions can be based on the interval needed to prevent flyspeck infection. 

    Scab can resurge in the fall as leaves get older and lose natural resistance.

 Flyspeck

    Risk of flyspeck infection was low until estimated availability of second generation spores beginning around July 8.  The infection risk level will increase another step with third generation spores estimated to become available starting around August 11. (Both dates are for Monmouth, see Orchard Radar for dates at other Maine locations.)

    Continuous protection against flyspeck is not necessary.  If a protection gap develops, application of one of the fungicides with 100 leaf wetness hour postinfection activity (Flint, Sovran, Topsin M) should prevent any flyspeck infections from taking hold.  In calendar days this is usually 10-14 days, but can be as little as 4-5 days with a spell of unbroken rainy, overcast weather. 

    Pristine is another strobilurin that has 100 LW postinfection activity against flyspeck, but given its cost and attributes it is best reserved for the final preharvest spray.

     Knowing that 2003 was a heavy flyspeck year, and that 2004 was apparently an average flyspeck year, I thought it would be interesting to evaluate this year's relative risk by comparing late July leaf wetness hour accumulations for 2003, 2004 and 2005.  But that didn't work, because that simplistic comparison did not reflect the much more problematic flyspeck in 2003. 

    But in every mistake is a lesson.  And the lesson this time is that it reminds me that the key factor that led to flyspeck problems in 2003 (and in Hudson Valley again in 2004) was not what happened between petal fall and late July.  The problem in 2003 was a drenching rain on September 4 that removed fungicide coverage, followed by unusually wet September weather until growers started noticing flyspeck on unharvested fruit showing up by the last week of September.

    Nobody likes to spray past mid-August as early cultivars mature and preparations for the main harvest require attention.  Unfortunately, it isn't possible to see far enough ahead to forecast unusually heavy flyspeck pressure until that situation develops.  One lesson learned from heavy flyspeck pressure in Hudson Valley in recent years is that renewing fungicide protection after heavy late-season rain removes coverage can make the difference between having or not having flyspeck problems show up several weeks later. 

    Depending on the wash-off date, if September weather following such an event is dry, or perhaps even normal, the investment in renewed protection may not prove worth the cost.  But if September turns out to be wet, then apples left unprotected after early fungicide depletion are much more likely to develop flyspeck by harvest.  A key difference that does show up in comparing Highmoor Farm 2003 and 2004 weather records is 25% higher September leaf wetness hour accumulation in the year with more common flyspeck problems.

    You can't predict how September rains will turn out, but what you can do is keep grass mowed and use summer pruning to reduce humidity in tree canopies.  Cultural measures alone can reduce flyspeck infection rates by 50%.

    You can also consider your expected harvest dates and make the final planned fungicide application late enough that protection should last until within 25-30 days of harvest.  That is because it usually takes at least 25 days after protection wears off for enough subsequent leaf wetness hours to accumulate to have visible flyspeck. 

    The duration guidelines used to estimate how long protection lasts have been shortened based on Dave Rosenberger's 2004 field trial observations.  For full strength captan, figure on 21 days or 2 inches of rain, whichever comes first.  Figure on the same residual protection from Topsin M 70WP at 3-4 ozs. / 100 gallons dilute (or equivalent of alternate Topsin formulation) combined with half rate captan.  For the strobilurins, figure on 21 days or 2.5 inches of rain whichever comes first.  Adding a sticker such as Bond may help prolong protection, but I don't know of data to demonstrate that.  

    If rain following your "last" fungicide application reduces the duration of fungicide protection to the extent that apples will be unprotected for more than 25-30 days before harvest, then it is time to start weighing the odds on whether an unplanned late August - early September fungicide update for blocks at risk is worth the time and trouble.  For small trees on a windy site the risk is much lower than for big, thick trees near the woods in a block where fog settles.

    Because of the 100 LW hour postinfection activity, such a renewal spray does not have to be made right after a big rain.  There can be an advantage to waiting a bit in order to apply after a rain within the 100 LW hour window and thereby not have the renewal application subject to depletion by that rain, with longer residual protection as a result.

    In addition to fungicide timing, another factor is fungicide selection.  The strobilurins Flint, Sovran, and Pristine, are the best products for prolonged protection from flyspeck.  Pristine may be even better than Flint and Sovran, and if applied within a week or two of harvest also offers protection against postinfection storage rots.

    Dave Rosenberger's article on flyspeck observations from 2004 trials is online at http://www.nysaes.cornell.edu/ent/scaffolds/2005/050620.html#disease

 Fire blight

     During the arctic conditions of bloom, I rashly prognosticated that at least we wouldn't have to worry about fire blight this year.  For the most part that was true, there were no major blossom blight incidents.  But right after bloom, trees that threw late blossoms were exposed to extreme fire blight weather.  The shoot blight that started showing up in early July might have also been caused as direct shoot infections, with the cloudy weather during bloom making foliage more tender and susceptible to shoot infection.

    If you find fire blight strikes, remove them as soon as possible and be sure to clean tools before reusing the tools on unaffected trees.  A few midsummer shoot strikes here and there is not the reason for fire blight's fearsome reputation, but it is something to address to prevent more severe problems next year.

    This episode shows once again that we can have fire blight weather in Maine, it just a matter of the right weather conditions lining up with bloom.  In the last few years we've had bad fire blight conditions just as bloom started and just after bloom.  It will happen right in the middle of bloom one of these years, which is why you want to keep inoculum down and be prepared to react in a future spring when those conditions develop. 

    European red mites were over threshold in four out of 36 blocks monitored in the past two weeks.  The threshold until August 15 is an average of 5 mites per leaf, or living hatched mites on more than 73% of middle aged fruit cluster and vegetative shoot leaves. 

    It is too late for best use of Agri-Mek.  There are numerous miticide options.  Nexter, Kanemite and Fujimite share a similar mode of action and so should not be used consecutively in order to prevent resistance.  The same is true of Apollo, Savey and Zeal.  Other options include Acramite, Kelthane, and Vendex.   Summer oil is yet another option, but cannot be used within 10 days of captan, or shortly before temperatures over 80 degrees.

    Codling moth adult first generation egg hatch is just about complete.  The next critical date for codling moth control is August 8/17/20, for Sanford/Monmouth/Old Town respectively, when second generation egg hatch reaches 7%.  That is a good date for application of Bt or other soft insecticide that requires multiple applications for control.  This is worth doing in organic blocks.

    For conventional blocks, first generation codling moth control and insecticide application for apple maggot is enough to keep codling moth from being a noticeable problem.  Apple maggot traps in three monitored plots at Highmoor Farm are over threshold in two of the plots, and still below in the third.  But the low counts in the third plot may be due in part to controls applied in plots on either side of it.  If you aren't using monitoring traps and have not applied insecticide for apple maggot, it is time to do so.

     This is the time to check 5 leaves per tree on at least 8 trees for sap-feeding leafminer mines on the bottom surface of leaves.  If you find 20 or fewer mines on the first 40 leaves, then it's a safe bet that there won't be any nasty surprises from leafminer moths fluttering to disturb pickers or be numerous enough to increase risk of preharvest drop.  If you find more than an average of 1 per leaf, that is getting into treatment territory, especially if trees are stressed or otherwise prone to early drop.

If above threshold, insecticide choices include: Assail, Calypso, Provado, Intrepid,
Lannate, SpinTor, and Vydate.

    Assail or Calypso would serve double duty as an apple maggot spray.  So would SpinTor but with somewhat less residual apple maggot control.  Vydate and Lannate are harsh on predatory mites.

    Treatment should be made before mines begin to show up on the upper leaf surface.

    Yet another summer insect pest is obliquebanded leafroller (OBLR).  It is a major pest in New York but has only popped up as an important pest in a few New England locations in the last two years.  The optimum sampling date for OBLR is past, but it is still worth taking a look.  If you find more than 3 infested shoots or damage apples per 90 shoots/fruit clusters, then treatment is advised.

    Japanese beetles have made their annual appearance.  Honeycrisp growers report that JB beetle especially target that cultivar. Soil treatments are not effective for orchard protection.  JB are very mobile and killing a few of the ones in the soil isn't going to have a significant effect on the number that fly in from afar and feed on foliage and fruit later on.  JB feeding appears as skeletonized leaves and ragged holes in fruit.  Early ripening fruit are most susceptible.
    There are numerous effective insecticide options, but Sevin (carbaryl) and Imidan have the advantage or shorter preharvest intervals at 3 and 7 days, respectively.  Be careful of longer preharvest intervals on other effective options such as  Assail, Calypso, Provado, or any of the pyrethroids.  Because of reinvasion, a treatment may not have appeared to have worked.  Repeated applications may be necessary.

 
    Another pest to keep an eye out for is potato leafhopper which may arriving with southwest winds. Potato leafhoppers characteristically move sideways on foliage when disturbed, and are light-green in color. They can be ignored for the most part on established trees, but can be significant pests of young apple trees, causing stunted shoot growth. If treatment is needed, Actara, Asana, Assail, Avaunt, Calypso, Danitol, Lannate, Provado, Thionex, Vydate and Warrior are all effective options.
 

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    There will be an orchard twilight meeting on August 9th, Tuesday at 5pm at the Treworgy Family Orchard in Levant, near Bangor.  Details later.
 

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Sincerely,                                            
Glen

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