Apple Pest Report:  Saturday, May 1, 2004
 Vol. 12 No. 1


 Scab 

     There have been two scab infection periods in the Sanford area.  The first started Friday April 23, the second started on Sunday April 25.   Because of early bud stage, cool temperatures during the wetting periods and scab ascospore maturity just getting started, these infection periods accounted for roughly 1% and 3% of the season's total primary (= first generation) scab infection risk.  As of Saturday afternoon, the next rain is forecast to begin Sunday night, May 2nd and to cause a major scab infection period in the Sanford area.  This infection period could deliver about 14% of the seasons infection potential. 

     If your trees are going into this infection period without full scab protection, then you should plan on application of a fungicide with post-infection activity (i.e. sterol inhibitor or strobilurin) as soon as possible after the rain.

     Another rain is expected to arrive Wednesday May 5.  The impact of that rain on scab risk may be reduced by the lack of time since the previous rain for more scab ascospores to mature.

     The situation is similar for the Monmouth area with the key difference being that with bud stage and ascospore development a few days behind Sanford, the relative risk of a May 2nd infection period is around 4% of the season's total.

     In a very clean orchard, the May 2nd infection period might not amount to much in the Monmouth area.  But in an orchard with high inoculum, and infection period accounting for even 1% of the season's potential can cause a scab outbreak.  The infection risk is directly related to how much scab is in the orchard. 

     While most orchards had good scab control last summer despite the wet spring weather in 2003, some scab always gets through in those conditions.  This was then exacerbated by the long wet spell in early August when it was difficult to impossible to renew fungicide coverage, and then exacerbated again by the heavy rains in September, just as apple leaves were losing their natural resistance to scab infections.  The only prudent assumption for spring 2004 is to assume higher than normal scab level in the orchard and manage accordingly.  That means keeping protective fungicide coverage renewed on foliage prior to all infection periods from now until at least 2 weeks after petal fall.

 


  Orchard Radar 

     You can see updated estimates for scab and other apple pests for four sites in Maine at the Orchard Radar pages for each site are at http://pmo.umext.maine.edu/apple/

 

 


  Borers 

    The following is from the April 26 Cornell Scaffolds fruit pest newsletter.
   "Early-Season Apple Borer Control
    (Dave Kain, Entomology, Geneva)

     There is increasing concern throughout the Northeast about damage done to apple trees by borers. A little over half of the trees on size-controlling rootstocks in New York have burrknots and about a third of those burrknots are infested by borers. The species of primary concern is dogwood borer, but American plum borer can be prevalent in western New York apple orchards that are close to tart cherry and peach orchards. While we do not yet fully understand the effects these borers have on dwarf trees, we do know that they reduce vigor and can, in time, completely girdle and kill trees.

    Over the last four growing seasons, we have tested a number of insecticides against these borers. Lorsban is very effective for this use and we would strongly urge growers to take advantage of it where needed. From 2001 to
2003 we tested some other materials, including white latex paint, endosulfan, Avaunt, Surround, Intrepid, Danitol, Imidan, Esteem and Spinosad compared with Lorsban, with varying results. To get right to the point, only Avaunt, Danitol, and Esteem, applied two or three times in midsummer, provided control comparable to one application of Lorsban.

     Borers can be controlled season-long by applying Lorsban at various times.
While postbloom trunk application of Lorsban is still allowed, applying this material early in the season, beginning as early as half-inch green, may be more convenient and will result in less damage than waiting until the traditional midsummer period. Lorsban infiltrates burrknot tissue and kills larvae concealed within. Early application will prevent feeding damage caused by overwintering dogwood borer larvae before the flight begins in late June. And, if American plum borer is a concern, the early application, in addition to killing overwintering larvae, will prevent infestation by the first brood of this pest, which begins at about petal fall. Lorsban is very persistent in wood so it continues to work for a considerably long time after it is applied (apparently 9-12 months in our trials). Other insecticides must be applied prior to borer oviposition and will protect burrknots only as long as they persist, so multiple applications will be necessary. In the case of dogwood borer this is most efficiently accomplished beginning at the time of the flight peak in mid-July, with another application in early August. This midsummer timing obviously will do nothing to control the first brood of American plum borer and will allow feeding by overwintered dogwood borer larvae to go unchecked up until that time. If you can, it would pay to take advantage of the window between now and pink to apply Lorsban for borer control in problem blocks."

     Lorraine Los of the University of Connecticut provided information for this addendum:
    
     The new Lorsban 75 WG formulation still DOES NOT have a supplemental label for borer use. It is only labeled for dormant/delayed dormant use on apples.  However you can use prior to bloom.  Alternatively, you can apply Lorsban for borer control after bloom if you have leftover Lorsban 50W or Lorsban 4E from last year. 

     There may be some concern of phytotoxicity if Lorsban 4E contacts flower buds during pink, especially if done in hot weather. Therefore, the 4E formulation probably should not be used beyond the tight cluster stage.

     Lorsban application for borer control should be directed to the lower trunk area. There should be little (if any) direct contact with the tree canopy. Lorsban rates are 1.5 quarts/100 gallons for Lorsban 4E or 1.5 pounds/100 gallons for Lorsban 50W. Specific use directions are on the supplemental label which must be in the possession of the user at the time of application.
 


 
 

Sincerely,                                            
Glen

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