Scab

       
        Scab levels were low in monitored orchards checked this week.  Even a block that had high levels of active scab earlier in the season showed a reduced number of infected leaves this week.  In blocks with low scab, fungicide protection against flyspeck should provide adequate protection against late season scab infection.
  

 

Flyspeck and Sooty blotch

       
        The peak risk period for flyspeck infection is August 1 - 31.  The conidia trapping data I have seen do not show a trend of higher aerial concentration of flyspeck spores as the summer progresses.  But by August flyspeck has had enough time (cumulative wet hours) to have gone through multiple generations to increase the distribution of source points for conidia to produce the next generation of infections. 

 

The surface area of a sphere increases in proportion with the square of its diameter.  So, as an apple doubles in diameter, its surface area quadruples.  More surface area means more places for flyspeck spores to land.  Apples in double-fruit clusters begin crowding against each other.  Apple tree canopies reach maximum density.  Fungicide protection has trouble penetrating to cover fruit, sunlight and air movement to dry fruit is blocked, and high humidity to foster fungal growth becomes trapped in the tree.

 

Flyspeck infections that start in August are likely to have enough time to accumulate the 270 wet hours required for the new colonies to become visible before end of harvest.  Of course, there is no such thing as an average year, and we do not know ahead of time how many wet hours will accumulate in August, September, and October.  For what its worth,  the one-month and three-month weather outlooks show Maine with normal chances for above or below normal precipitation in August, and also for August-September-October.

 

If normal precipitation patterns do occur, then flyspeck infections that begin on unprotected fruit on August 1 could become visible on fruit by around September 9.  Infections that start August 31 could become visible on fruit by around October 9.  Growers putting fruit into storage need to consider the possibility of fruit accumulating wetting hours from condensation in storage before temperatures drop too low for flyspeck growth.  Subtracting 50 wet hours from the allowable preharvest accumulations means that infection start dates of August 1 or 31 allow risk of “too much flyspeck development” for harvest dates of September 1 and October 1, respectively.

 

The point is that for fruit that will not be harvested until late September or early October, it is important to maintain fungicide protection against flyspeck infection until at least August 31.  If wet weather predominates in September, an even later fungicide depletion date might be desired.  The flyspeck respray interval estimates at http://pronewengland.org/AllModels/MEmodel/RADARME-MonmouthLate.htm#FLYSPECK will reflect new weather observation and forecast values as they arrive.  The charts can be used two ways.  One way is to look up the date of the most recent fungicide application to get an estimate of when it is expected to lose its ability to prevent new flyspeck infections.  To avoid a gap in protection, this indicates when the coverage should be renewed.  

 

The other way to use the tables is to look up prospective dates for a final fungicide application to see how late into September and October such an application would provide reasonable surety of there not being a flyspeck problem, and comparing that “latest safe harvest date’ with your expected harvest dates.

 

A strobilurin fungicide (Flint, Sovran, Pristine), or Topsin (in combination with Captan or Ziram), will provide protection against flyspeck for 21 days or two inches rain, whichever comes first.  Pristine also provides protection against storage fruit decays caused by Botrytis and Penicillium fungi.  However, it costs more than the alternatives.

 

Captan or Ziram used alone at full-dose can be relied upon to protect for 14 days or two inches rain, whichever comes first.

 

Preharvest intervals for the materials listed above, and the estimated cost for enough material to treat an acre of large 300 dilute gallons per acre trees are show below.  Except for Pristine, smaller sized trees would have correspondingly lower dose cost per acre.

 

Strobilurins – 21 days, 2 inches rain
Flint at 0.8 oz./100 gals., 14 days, $30
Sovran at 1.6 ozs./100 gals.– 30 days, $30
Pristine* at 14.5 – 18.5 ozs. per acre – 0 days, $36 - $46 (*using less than 14.5 oz./acre for smaller trees is prohibited by label)

 

Topsin combinations – 21 days, 2 inches rain
Topsin 70WSB at 4 ozs./100 gals. + Captan 50 at 1 lb./100 gals. – 0 days, $24
Topsin 70WSB at 4 ozs./100 gals. + Ziram 76DF at 0.75 lb./100 gals. – 14 days, $22

Captan or Ziram alone – 14 days, 2 inches rain
Captan 50WP at 2 lbs./100 gals., Captan 80WDG at 1.25 lbs./100 gals.– 0 days, $19
Ziram 76DF at 1.5 lbs./100 gals. – 14 days, $14

 

Warm September?

   

Speaking of long term weather outlooks, the one-month temperature outlook for August shows a 50:50 chance for above or below normal temperatures.  The August-September-October temperature outlook shows Maine with increased chance of warmer than normal temperatures during that period, with September seeming to be the key month.  Forecasts are far from perfect, and Outlooks are not even forecasts.  The September one-month outlook is scheduled for August 17, and will be available at http://pmo.umext.maine.edu/apple/forecast.htm.    

 

    

 

Insects and Mites

       

        No new apple maggot flies were caught on 12 traps at Highmoor Farm from July 18 to July 24.  As of Monday July 24, a total of only 3 AM have been caught on the 12 traps, for a cumulative average of 0.25 per unbaited trap.  The recommended treatment threshold is when cumulative average captures reach 1-2 per unbaited trap.

 

        If you have your own traps, make sure you can distinguish apple maggot from the myriad other flies and insects that are caught.  Apple maggot flies have a distinctive wing pattern, but that pattern is often hard to see on trapped flies.  There are other flies that have similar, but not exactly the same, patterns.  Apple maggot flies also have a white dot on the upper thorax, and a horizontal light colored line along the side of the thorax that starts just behind the compound eyes.  This characteristic is often visible when the other two are not.  There is a picture of a trapped apple maggot fly on the Apple IPM Scouting Card at http://pronewengland.org/INFO/PROpubs/AppleScoutCard-2006.pdf

 

        If apple maggot control is needed, choice of insecticide may be a bit less critical than with other insect pests because apple maggot flies are relatively easy to control.  Thus, even products without the highest efficacy rating will be effective, just for a less extended period.  The top rated materials for apple maggot control include Imidan, Guthion (azinphosmethyl), Diazinon, Dimethoate, Assail, or one of the pyrethroids (Asana, Danitol, Warrior).  Calypso has similar activity to Assail, and might be included in the top group. 

 

Sevin (carbaryl), Lannate, Avaunt, and SpinTor are in the second tier of efficacy.

 

        Sevin (carbaryl), Diazinon, Dimethoate, and especially the pyrethroids (Asana, Danitol, Warrior), have increased detrimental effects on beneficial arthropod insect and mite predators and parasitoids.

 

Preharvest intervals for the materials listed above, and the estimated cost for enough material to treat an acre of large 300 dilute gallons per acre trees are show below.  Smaller sized trees would have correspondingly lower dose cost per acre.

Organophosphates

Imidan – 7 days, $21-$27

Guthion - 14 days (21 days if higher rate is used), $22-$24

Diazinon – 21 days (but check label), $23

Dimethoate – 28 days, $16

 

Thiacloprids

Assail – 7 days, $42

Calypso – 30 days, $25-$51

 

Indoxacarb

Avaunt – 14 days, $28

 

Spinosad

SpinTor, Entrust – 7 days, $21-$43

 

Carbamates

Sevin (carbaryl) – 3 days, $11-$22

Lannate – 14 days, $19

 

Pyrethroids

Asana – 21 days, $5-$16

Danitol – 14 days, $11

Warrior – 21 days, $5-$10

 

       

        European red mite should be at the yearly peak now, but populations in blocks monitored July 24-27 were very low.  The recommended treatment threshold for August 1 -15 is an average of 7.5 living hatched mites per leaf, or an average of 86% of leaves in a 100-leaf sample have mites.  For a smaller 40-leaf sample, treatment is not recommended if 27 or fewer of the 40 leaves have mites present.

 

 

Proposed Imidan label changes

 

        August 8 is the final day that EPA will collect comments for proposed changes to future Imidan insecticide labels.   

        Imidan insecticide has been an important IPM tool in Maine apple orchards for many years.  EPA has proposed label changes that if adopted would significantly reduce its utility for many Maine apple growers.  The manufacturer of Imidan (Gowan Company) is rebutting the proposed Imidan label changes for a 7-day REI and prohibition on use in pick your own orchards.

 

Individual letters from growers explaining how the proposed changes will affect your operation can influence the final EPA decision.

 

Here are steps to submit a comment to EPA:

 

1. Go to http://www.regulations.gov/fdmspublic/component/main

 

2. In the box labeled “Keyword or ID” enter the Imidan docket number:
EPA-HQ-OPP-2002-0354   

 

3. Click on the “Submit” button in the lower right hand corner of the page.

 

4.  On the new page that opens, click on yellow button on the right side where it says “Add Comments”.

 

5.  This opens a new page where you can give your organization and name (not required), and a box where you can write or paste in your comments.   
     You must enter something in the comment box.  If you want to write a letter beforehand, you can just enter "Please see attached letter" in the comment box, and then upload the letter as a Word, WordPerfect, or Text file.  In case they have trouble opening an attached letter file, it may help to enter your email address in the comment box so they can contact you if there is a problem. 
     To submit a letter as an attached file, click on the "browse" button to find the document file on your computer, then click “Open”, then click on the “Add Attachment” button.

 

6.  After entering text in the comment box (and uploading a letter file if you choose to do that), click on "Next step" button in the lower right hand corner of the page.

 

7.  On the next page that appears, the final step is to click on the “Submit” in the lower right hand corner.  This sends your comments to EPA.

 

It may also help to send a copy of your comments to Jim Cranney at US Apple: jcranney@usapple.org

 

One person’s perspective on possible consequences from the proposed Imidan label changes is described in this letter.  ( http://pmo.umext.maine.edu/apple/ImidanLetter-2006-07-25.htm )