Apple Pest Report:  Friday, July 1, 2005
Vol. 13 No. 7

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     About 80% of the season's primary scab infection potential has had to appear as 2nd generation lesions in Maine orchards as of July 1. But infections from the May 17-30 rains which created the season's most serious infection risk (due to inability to renew rain-depleted coverage) have had time to appear as 2nd generation lesions. 

     If thorough orchard scouting finds fewer than 5 scab-infested leaves per 100 shoots, then fungicide respray decisions can be made on the basis of flyspeck control.  However, scab scouting should continue until all of the season's primary scab infection potential has had time to appear as 2nd generation lesions.  First generation lesions in the tops of trees may not make their presence known until they have had time to wash conidial spores down into the canopy that then develop into 2nd generation infections.

     If you find more than 5 lesions per 100 shoots, then scab suppression treatments will be needed to protect the crop.

The following article is by Dr. Dan Cooley, University of Massachusetts.

"Getting a Handle on Scab

By now, if you have any scab in your orchard, it should be
visible. Thanks to the long, cool, wet weather during May, there’s a
little more scab than usual in some orchards, and plenty of scab where
trees were left unprotected or a critical spray was missed. If there is
no scab visible after you’ve taken a good look at trees, including
insides and tops, then you don’t need to read any further.

However, if you have some scab on leaves and/or fruit, what should be
done? First, don’t panic. The best indicator of how much scab you will
end up with at harvest is the amount of scab on fruit in
mid-season. So, if you have some scab, but it’s all on the leaves, then
there’s a good chance, with a regular fungicide program, that fruit at
harvest will be relatively scab-free. A lot of scab on fruit now
indicates a more serious problem (resistance, poor calibration, bad
timing), one that should be looked into and resolved before next year.

To decrease scab pressure on the leaves, start with a full rate of
captan on a relatively hot day, when temperatures are 80ºF or more. The
full rate is 1.25 lb. Captan 80 WP per 100 gal., or 2 lb. Captan 50 WP
per 100 gal., or 2 pt. Captan 4L. After 7 to 10 days, as second
fungicide application should be made. The first choice would be a full
rate of Sovran or Flint plus a half rate of captan. Sovran 50WG should
be applied at 1.6 oz. per 100 gal.; Flint 50WG should be applied at 0.8
oz. per 100 gal. A second choice, if the maximum number of strobilurine
applications has already been made, or if scab is relatively light,
would be a second full rate application of captan alone.

Some will ask “What about Topsin? Doesn’t it eradicate scab?” Yes, as
long as the scab hasn’t become resistant. If Topsin-M 70WP is used, it
should be applied at the full rate, 3 oz. per 100 gal., and it should
be applied with a half rate of captan. 

As fruit sizes and tissue matures, it will become more resistant to
scab. After the two eradication sprays, regular cover sprays that
include a half rate of captan at 2 to 3 week intervals should be
adequate to protect fruit into harvest. After harvest, it will be time
to consider ways to destroy scab inoculum before it can cause problems
next season."

 Flyspeck

    If apple scab is under control, then the focus of disease management can switch to preventing flyspeck.  Preventing flyspeck will also prevent sooty blotch. 

     Full dose captan protects against flyspeck infection for up to 21 days or 2 inches of rain, whichever comes first.  Full dose Sovran or Flint are even better against flyspeck, protecting for 21 days of 2.5 inches of rain. 

      It takes a 2 - 6 weeks for the flyspeck fungus, growing in the waxy cuticle on the surface of the fruit, to become visible.  The length of the development period is controlled by the accumulation of approximately 270 wetness hours when moisture is freely available on the surface of fruit.

    During the first 100 wet hours after infection, the fungus can be killed with a postinfection application of Flint, Sovran or Topsin M.  The Topsin M should be used at 3-4 ounces per 100 gallons dilute, and combined with a half rate captan.

     The longer protection offered by fungicide against flyspeck, combined with the opportunity for postinfection control, creates opportunity for a long interval between fungicide applications from late June well into July where apple scab is under control.

     At Highmoor Farm for example, full dose captan was applied on June 19.  With orchard monitoring showing that only a few scab lesions are present, the current outlook is that protection from the June 19 spray will be depleted around July 8, and that a postinfection application of Flint, Sovran or Topsin could be made as last as July 22 with minimal risk of flyspeck development.

     A long interval between fungicide applications can turn into a long interval between spray trips if insects and mites also do not require control.

         The control window for plum curculio ended Wednesday June 22 in Sanford, June 27 in Old Town.  Plum curculio are still active in unsprayed plots, but where there was insecticide protection from petal fall until the end of the control period, a high enough percentage of plum curculio should have been killed to eliminate significant risk of further damage.  Organic growers should continue Surround coverage for another couple of weeks at least for full suppression. 

    Codling moth adult emergence begins at petal fall, and is now 91% and 77% complete in Sanford and Old Town, respectively.  While codling moth are numerous enough to cause serious damage, they do not do so presumably because insecticide applications made for plum curculio decimate the adult codling moth population before they can lay eggs.

     But where this indirect control does not occur because Surround or nothing was used to deter plum curculio, codling moth egg hatch is now at roughly 54% in Sanford and 25% in Old Town.  Organic growers should either continue Surround coverage which is moderately effective at preventing 1st generation codling moth damage, or target sprays at killing codling moth larvae.  Entrust or Bt sprays at weekly intervals should be effective.  Due to short residual efficacy, Pyganic is probably not as effective.

    Apple maggot (AM) fly is the next major pest on the horizon.  Emergence varies from year to year, being typically a bit later in dry years.  Given the soggy soil conditions this year, emergence may begin a few days earlier than the estimated date (July 9-Sanford, July 15-Old Town).  Sticky ball traps can tell you when enough AM have arrived to require protection. The threshold is an average of 2 AM flies per trap.  It is not unusual to not reach threshold until July 20 or later at Highmoor Farm.  Monitoring with sticky ball traps also helps minimize follow-up applications. 

    Alternatively, perimeter row treatments can be used to kill AM as they migrate into the orchard.  This strategy requires having protection in place at the beginning of emergence.

     Plum curculio and apple maggot sprays also indirectly kill roundheaded apple tree borer and dogwood borer adults.  Specially targeted trunk sprays for these pests are not normally needed where insecticide applications for plum curculio and later apple maggot keep them in check.  But borer damage can be devastating to young plantings and in organic orchards where foliar insecticides are not applied. 

        In the Monmouth, the rough guess for beginning of roundheaded apple tree borer egg hatch is July 7.  Peak egg hatch is from late July through the middle of August.

     The first line of defense is to prevent thick weed growth from shading the lower trunks.  Likewise, spiral close-fitting "mouse guards" should be removed in the summer.  Hardware cloth or other mouse guards that allow light and air to reach the trunk are preferable, but do not let vegetation grow into the space between the trunk and the guard.

    For conventional young blocks not receiving insecticide coverage because they are not yet bearing, specially targeted borer control is needed.  A prebloom trunk application of chlorpyrifos (Lorsban) offers season-long protection.  Neither Lorsban 75WG (dry formulation) or Lorsban 4E liquid formulation label allows use on apples after bloom.  A supplemental label to allow postbloom trunk application with the dry formulation was lost when Gowan bought exclusive distribution rights.  It may be back in 2006, but for 2005 Lorsban 75WG cannot be applied after bloom. 

     A supplemental label for postbloom trunk application with Lorsban 4E label is online at http://www.cdms.net/ldat/ld02A039.pdf .  The supplemental label must be in possession of the user at time of application.  It allows application from no more than 4 feet away to the lower 4 feet of trunk, with no spray to contact foliage or fruit.

    The next best option is trunk application of Thiodan 50WP in early July and again in early August.  A pesticide applicator's license is required to purchase Thiodan.  Application of Imidan (or one of the premixed home fruit tree spray products that contain an insecticide) to the trunks every two weeks should also keep borer damage. 

    For organic orchards, bearing or nonbearing, borers are probably the number one pest.  This is especially true on young trees with less than 4 inch trunk diameter.  White latex paint mix 50:50 with water to create a whitewash can be applied to the trunks to deter borers, and also to make them more visible where they push out frass (chewed wood.)  Trunk application of Aza-Direct, Bt and Pyganic would all be ineffective.  Entrust might offer some protection, but I don't have any information to back that up.

    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.  OBLR egg hatch is expected to begin around July 6-11 (Sanford-Old Town).  Where OBLR has been a problem and control with standard insecticides has not been effective, egg hatch is the time to target small larvae with Bt, Intrepid, SpinTor, or Esteem.  A pyrethroid (Asana, Danitol, Decis, Proaxis, Warrior) would also be effective, but harmful to mite predators. 

    If OBLR have not been a problem in the past, the optimum monitoring date is July 15-20 (Sanford-Old Town).  If more there are more than 3 infested shoots or damage apples per 90 shoots/fruit clusters, then treatment is advised.

    European red mites were over threshold in several monitored blocks this week.  The current threshold is an average of 2.5 mites per leaf, or living hatched mites on more than 54% 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 exceed 80 F.

Sincerely,                                            
Glen

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