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					  Apple Pest Report: Tuesday, July 20, 2010
  Vol. 18 No. 7

  Fire blight
                                                                      Fire blight shoot blight strikes are
Fire blight photos by NY State Ag. Exp. Sta.   showing up in at least eleven Maine
                                                                orchards, and there are probably others.
                                                                None of the orchards with shoot blight had
                                                                noticeable blossom blight, so presumably
                                                                the inoculum for the shoot blight infections
                                                                came from overwintered canker infections
                                                                in the orchard. Blossom blight infections on
                                                                trees in the nearby woods are another
                                                                possibility, but that seems less likely.

                                                                In some cases it seems that the
                                                          location of the shoot blight within the
                                                          orchard is associated with June pruning cuts
  which may have provided entry sites for fire blight bacteria, similar to the way that hail damage
  can lead to shoot blight. Fire blight bacteria need an open wound (or open flower during bloom)
  to gain entry into the trees’ vascular tissue. Even wind whipping of foliage can provide such
  wounds, but the risk is much higher with hail damage.

        Application of streptomycin within 24 hours after hail damage can help prevent such shoot
  blight infections. But once shoot blight is found, streptomycin application is useless and will only
  help breed resistance in the bacterial population. Streptomycin is no longer effective in some
  areas (none in Maine fortunately) from such overuse.

        Sanitation pruning is needed where shoot blight occurs. The following is adapted from “An
  Annual Fire Blight Management Program for Apples” by D.R. Cooley, W.R. Autio, J.M. Clements, W.
  P. Cowgill, Jr., and R. Spitko. The full document is online at
         When pruning fire blight, the best method to use is the “ugly stub” approach. To be most
  effective, strikes should be pruned out as soon as symptoms appear, and daily checks made to
  remove diseased shoots.
               Make cuts into wood that is at least two years old. Two-year-old wood is more resistant to fire
        blight, and is much better than younger wood at stopping infection movement in the tree. Fire blight
        bacteria travel well ahead of visible infection, up to several feet. Cutting back to a 4 to 6 inch naked
        stub in 2-year-old or older wood gives the tree a good chance of using its own resistance to isolate
        disease in the stub.
               Inevitably the fire blight bacteria will form a canker an inch or two in from a cut surface.
        Sterilizing tools will not stop this, so it is not worth the effort. As a result, if a flush cut is made back
        to the branch collar, the resulting bacteria colonization and canker will form an inch or two into the
        next limb or in the trunk. By leaving a stub, the canker forms in the stub, which can be removed
        during winter pruning. (Cuts made in the winter when the disease is not active will not cause a
        canker near the cut). Spray painting the ugly stubs with a bright color during sanitation pruning
        makes them easy to find and remove during winter pruning.

              If sanitation pruning is done during hot dry weather, the cuttings should not remain a source
        of bacteria for additional infections for more than a day, but it seems wise to do all you can to
        reduce the chance for further spread by removing the cuttings from the orchard and burning or
        burying them. Cutting blades do not need to be sterilized between cuts, but should be sterilized
        before reusing those same tools on unaffected tissue.

              The loss of branches and the expense of sanitation pruning due to shoot blight is one impact.
        Sanitation pruning of scattered strikes is worth the effort. If left in the orchard the infected tissue
        would provide cankers and inoculum potential for more shoot blight this summer, and
        overwintering sites for fire blight cankers with much higher risk of severe blossom blight infection
        in the following years. The risk of shoot blight declines as trees reach terminal bud set.

              The 2010 Maine shoot blight outbreaks mentioned above are not severe, but the idea that
        there are enough overwintered fire blight cankers around to create noticeable shoot blight in this
        many Maine orchards is discomforting. It suggests a statewide rise in background inoculum level
        and the need for close attention by all Maine apple and pear growers to watch for fire blight
        cankers, shoot blight strikes, and for blossom blight infection periods. Of course watching only
        makes a difference if you are prepared to act on what you see. Timely streptomycin application to
        prevent blossom blight, and sanitation removal of blossom and shoot blight strikes that occur can
        be very profitable investments that prevent extensive damage. Avoiding excess nitrogen and
        pruning practices that lead to excessive and prolonged shoot growth is also important.

Fire blight photos by NY State Ag. Exp. Sta.
Mystery dieback
      An unidentified dieback is being reported from Michigan and New York McIntosh trees. An
unusual number of dead limbs has been noted on McIntosh and other cultivars in Maine in a few
locations. Whether the two situations are related, or the cause of either, is unknown. It could just
be winter kill, but the distribution of damage doesn’t seem to fit the normal winter damage
scenario. The unusually prolonged wet conditions in June and July 2009 could be a factor,
perhaps by favoring growth of Nectria fungus that normally is a weak pathogen, but under last
year’s wet conditions, Nectria may have been able to only to cause constrictive cankers are
otherwise weaken trees and interfere with hardening off before winter. Or the Nectria found on
some dead branches could just be secondary infections of already weakened wood.
      If you had unusual dieback this year, I would appreciate hearing about it. If new symptoms
appear, it might be worth sending in samples for examination, though even if caused by a disease,
identifying the cause of dieback is difficult.

Apple scab
      Scab levels are generally low. If more than 5 – 10 active lesions can be found per 100
shoots, then two captan applications about 10 days apart can prevent further spread. Otherwise,
fungicide application to prevent flyspeck and sooty blotch should be adequate to prevent spread
of secondary scab.
      Hobbyist growers who have not had success controlling apple scab despite making
applications of alternative products that list scab on the label might be interested to know that the
EPA does not require efficacy data before issuing label, and that some of the products labeled for
controlling apple scab are not effective.

Flyspeck and Sooty Blotch
       The period of highest risk of flyspeck infections began July 10. Flyspeck infections that begin
on unprotected apples before mid-August have a good chance of becoming visible on apples by
September 20. Flyspeck infections that begin on unprotected apples before the end of August
have a good chance of becoming visible by October 20.
       Options for effective control of flyspeck and sooty blotch, and their relative durability, and
preharvest intervals are as follows. The phosphite fungicides include Agri-fos, Fungi-Phite,
Phostrol, ProPhyt, and Topaz. Cabrio is registered for use in Maine on apples, but I have not
found the supplemental label that includes apples. Cabrio has the same strobilurin active
ingredient as Pristine.
                                       Inches     entry interval       Preharvest
Fungicide(s)                Days        rain          (hours)        interval (days)
Pristine                     21          2.5            12                  0
Flint                        21          2.0            12                  14
Sovran                       21          2.0            12                  30
thiophanate (Topsin M,       21          2.0          12 – 48        1 day but check
etc.) + captan                                                            label
phosphite + captan           21          2.0            24                  0
captan alone                 14          1.5            24                  0
      The following is adapted from an article by Annemiek Schilder of Michigan State University
in the May 11 Fruit Crop Advisory Team Alert.
Use strobilurin fungicides wisely to avoid fungicide resistance development
      Strobilurins are fungicides that are modeled after an antifungal substance produced by a
small forest mushroom called Strobilurus tenacellus. This mushroom grows on pine cones and
uses an antifungal substance to suppress other fungi which may be competing for the same food
source. Synthetic strobilurins were made to be more resistant to UV light degradation than the
natural chemical produced by S. tenacellus. All strobilurins have the same mode of action, i.e.,
they inhibit the electron transfer in mitochondria, disrupting respiration and thereby causing the
fungus to run out of energy and die.

       The strobilurins include azoxystrobin (Abound), kresoxim methyl (Sovran), pyraclostrobin
(Cabrio) and trifloxystrobin (Flint). Pristine is a mixture of pyraclostrobin and boscalid. Boscalid is
not a strobilurin but belongs to the carboxamide chemical class. Adament is a mixture of
trifloxystrobin (Flint) and the DMI fungicide active ingredient in Tebuzol.

       Some of the strobilurins have phytotoxicity to certain plant species. Abound is phytotoxic to
apples, Sovran is phytotoxic to certain sweet cherry varieties, Pristine and Flint are phytotoxic to
Concord grapes. Caution must be taken when applying these products in the vicinity of
sensitive crops (or using the same sprayer to treat a sensitive crop after previous use of a
strobilurin phytotoxic to that crop.)

       Strobilurins become rainfast quickly and have translaminar activity, which means that they
can move from one side of a leaf to the other, providing disease control on both leaf surfaces.
Strobilurins have an outstanding ability to inhibit spore germination, thus they should be most
useful early in disease development. They do not have much post-infection activity. Some
strobilurins (e.g., Abound and Flint) are listed as “reduced-risk” by the EPA, which means that they
have relatively low mammalian toxicity. However, they are toxic to fish and other aquatic
organisms, so regulations must be followed for use around bodies of water.

       Since strobilurins have a site specific mode of action, they are prone to fungicide resistance
development in target fungi because a single mutation in a fungus can block their action. Where
strobilurin resistance has occurred, the pathogen strains have exhibited a high level of resistance
that cannot be overcome by increasing the fungicide application rate. Continued and exclusive
use of strobilurin fungicides may allow resistant strains to build up over time and may lead to
control failure and loss of the fungicide as a disease management tool. Strobilurin resistance has
been reported in grapevine powdery and downy mildew in various eastern US states and has
also been confirmed in grapevine powdery mildew in Michigan. Strobilurin resistance has been
reported in Colletotrichum acutatum in strawberries in Florida. (And shifts toward resistance have
been documented in apple scab populations, including Maine sites).

      The goal is not to manage resistance once it has developed, but rather to prevent or delay
the development of fungicide resistance in the first place. To do this, it is important to limit the
number of strobilurin applications. A good guideline is for strobilurins to make up no more than
1/3 of all fungicide applications during the growing season. In addition, regular disease scouting
to determine the actual need for fungicide sprays and nonchemical management practices, such
as sanitation, canopy management, and biological control are also important.

      Do not use more than four total applications and two sequential applications of any strobilurin
fungicide per season. Tank-mixing strobilurins with other fungicides is usually not necessary or
cost-effective since they already have a broad spectrum of activity.

      If flyspeck has been a problem in the past, your best bet is to save at least one slot for use of Pristine
or another strobilurin in mid to late August.
      The Orchard Radar flyspeck tables can help identify earliest safe final fungicide application date.
Monmouth -
Sanford -

Insects and Mites
      Apple maggot trap captures are moderate so far, but there really isn’t much point in talking
about statewide conditions for this pest because population levels vary so much between
locations. AM trap captures typically peak in late July and early August. If you don’t have traps up,
you should treat soon. Pyrethroids are rated good for AM control, I don’t know about the newer
ones, but the older pyrethroid products like Asana are thought to lose some efficacy when
temperatures are in the 80s. More on insecticide options coming soon.

       Woolly apple aphids began showing up in late June. As the season progresses they are more
likely to be found on water sprouts and pruning wounds. The old threshold for WAA was to treat
if more than 50% of pruning cuts had WAA. But you might find fruit staining from their droppings
before they reach that level, and there is the unknown factor of what their underground feeding
does to tree roots. Diazinon and Movento have good efficacy against WAA. Assail, Calypso,
Beleaf, Provado, and Thionex have Fair efficacy. Because of their waxy coating, thorough soaking
coverage is required to get good control.

      Two spotted spider mite populations usually don’t build until the end of a dry summer, but
they have already increased to threshold levels in a couple of Maine orchards. The threshold for
European red mites and TSSM from July 15 to August 15 is 76% of middle aged leaves with living
hatched mites.
      Acramite, Kanemite, Portal, and Zeal are the most effective miticide options for TSSM.
When young, the small spots on TSSM nymphs are difficult to see without magnification.
      ERM populations typically peak with the 4th generation in July.

      Shallow scraping feeding pear, cherry, and plum trees is likely caused by pear sawfly larvae
that look like quarter inch long gobs of slime. They are easily controlled by a wide range of
insecticides, or in a backyard planting by dislodging them with a hose spray.
Pesticide News
1) Final 2010 Spray Notification Registry
     The sign-up period for the Maine Notification Registry for Aerial or Air-Carrier Pesticide
Applications was extended until June 15, and the finalized 2010 list was posted July 1. Orchardists
using airblast sprayers are required to identify and give prior notice to any persons on the list
whose location is within 500 feet of where airblast sprayer will be used. The list and notification
requirements are available at

2) Public Comments Solicited for a Comprehensive Pesticide Application Registry
      Before the no-fee registry for notification about agricultural pesticide applications made
with aircraft or air-carrier sprayers that began this year, there was a $20 per year registry to be
notified about commercial lawn and ornamental pesticide applications.

      Creating the new agricultural spray notification registry this spring resulted in two parallel
but different registries. The Maine Board of Pesticides Control (BPC) is interested in ways to
operate a single registry, address concerns about other types of pesticide applications, and settle
the temporary measures invoked by LD 1293 last winter into more permanent and consolidated

      The BPC is holding a public comment session to solicit input about pesticide notification
regulations on Friday, July 23 at 9:30am in Portland at the Howard Johnson Plaza, 155 River Street.

       Here are some items from a recent BPC memo of ideas being considered:
       - Create a single registry for non-agricultural and agricultural pesticide notification. The
comprehensive registry should have no fee for participation, and an internet based sign-up and
distribution system.

      - Require notification for applications made with powered boom sprayers. I think this is the
most significant idea in the memo. Relatively few crops and farmers use airblast or aerial
applications, but almost all farms use boom sprayers. If carried through into legislative proposals,
requiring notification requirements for boom sprayer applications will create much political

      - The new unified system would have three notification distances
          1) 1,320 feet for aircraft and air-carrier equipment, with exceptions. (Presumably, the
current exceptions of 500 feet for fruit trees and Christmas trees would be continued).
         2) 500 feet for ground-based, powered application of liquid pesticide (i.e. boom sprayers).
         3) 250 feet for non-agricultural (urban/residential) commercial applicators.
      The rationale for a smaller distance for applications in urban/residential areas is that those
areas are characterized by small lots, many buildings, and the prevalence of shade trees.

     - The sign-up system would prompt participants to select the types of applications for which
they want advance notice. If participants select residential/urban applications, they will be
responsible for listing the addresses within 250 feet from which they wish to receive advance
notification of pesticide applications. Requiring registrants to identify potential spray application
sites only applies for applications made in a recognized urban/residential zone.
       For agricultural applications, it is the applicator responsibility to check the registry and find
registrants within notification distance of the application site.

      - Land managers would not be responsible for notifying registry participants if the contact
information is invalid. Include provisions for emergency waivers and same day notification for
urgent needs consistent with IPM.

3) EPA is currently working out the details of a decision to eliminate use of endosulfan (e.g.
Thionex) because of risks to agricultural workers and wildlife.

Upcoming events
1) Organic Orcharding Meeting at Highmoor Farm, July 21.
      Hosted by Dr. Renae Moran as part of a cooperative research project with the University of
Vermont. Dr. Lorraine Berkett and Terry Bradshaw from the University of Vermont.
       9:00am – Coffee and donuts
       9:30 – Diseases and Problems in Organic Apple Orchards, Loraine Berkett
      10:00 – Experiences with Seaweed Products, Terry Bradshaw
      10:30–11:00: Walk or drive to organic apple block
      11:00–12:00: Orchard Tour and discussion of apple research, Renae Moran and Greg Koller

2) Maine State Pomological Society Annual Meeting and Summer Farm Tour at Lakeside
Orchards in Manchester ME on July 28
 Hosted by Steve and Marilyn Meyerhans
  9 am Coffee and registration
 9:30 GAP Certification. Linda Titus, AgMatters
10:00 Labeling and Testing Food Products. Beth Calder and Al Bushway, UMaine Dept. of Food
Science. How to properly label a value-added food product and how the UMaine can help.
10:30 Break
10:45 The Bee Situation. Tony Jadczak, State Apiarist. The current status of honeybee hives and
pest management practices.
11:30 Bystander Risk. Lebelle Hicks, State Pesticide Toxicologist. Commonly used pest control
materials and their risk to bystanders who could potentially come into contact with them in and
around an orchard.
12:15 Maine State Pomological Society business meeting and Lunch
1:30 – 3:30 Orchard tour. Steve and Marilyn Meyerhans, and pest management update with
Glen Koehler, UMaine Cooperative Extension.

Closing words
“That's one small step for [a] man, one giant leap for mankind”
Neil Armstrong           (the “a” was lost in transmission due to static).
Glen W. Koehler
Associate Scientist IPM
Voice: 207-581-3882 (within Maine: 800-287-0279)
Pest Management Office, 491 College Avenue
Orono, ME 04473-1295

Putting Knowledge to Work with the People of Maine

A member of the University of Maine System
Nondiscrimination statement, disability resources, nondisclosure statement

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Description: Apple pest report spread