L.P.Berkett, IPM Specialist

June 10, 2002

Disease Management

 Apple Scab –    In non-sprayed McIntosh trees, scab lesions are very easy to find on cluster leaves, on the leaves near the base of vegetative shoots,  and on the fruit.   On the fruit,  lesions are located right at the sepal end of the fruit or on the side of the fruit.  The lesions start out as dark greenish spots which eventually turn velvety and more greyish.    Infections that occurred on May 30-31 should be showing up as lesions within the next few days if they are not already present.

Powdery Mildew:  Powdery mildew can be easily seen on some cultivars -- both where it overwintered (i.e., primary infection sites)   and secondary lesions on the underside of leaves.    Primary infection sites differ from   secondary lesions in that the primary sites usually involve a cluster or vegetative shoot where all or most of the leaves are covered with the white mycelium (both the top and the bottom sides of the leaf).  This indicates that the mycelium had overwintered in the bud and as the leaves developed, the fungus spread on the leaf surface.  Secondary lesions usually form from conidia that are carried to the leaf by wind;  the lesions look like white patches which are usually on the undersurface of the leaf.   Please see earlier Newsletters and Alerts concerning fungicide options.

Arthropod Management Update:

Codling Moth:  As was described in the last IPM Alert, if CM is a problem in your orchard the first insecticide targeted at this insect should be applied at 250 DD (base 50 F)from first sustained pheromone trap capture(biofix), which corresponds with predicted 3% egg hatch.  A second spray may be applied 10-14 days later.  If pressure is not too severe, one spray will suffice, applied instead at 360 DD after the biofix date.   At the UVM Hort. Res. Center,  as of this morning,  we had accumulated 214 DD from May 7th which was our biofix date.

Plum Curculio:  We are seeing more ovipositing damage this year than we have for the past two years on non-sprayed trees.  As of this morning,   we were still seeing fresh scars --- see picture below.     Fresh scars can be distinguished from older scars by lack of corking and often the presence of a droplet of clear ooze that turns yellow before it dries up. 

Research at Cornell has shown that maintaining insecticide residue until  340 DD base 50 F after petal fall is effective in preventing damage from this insect.   This DD relates to when 40% of cumulative feeding and oviposition has occurred.  The following is an estimation of the DD at 5 sites around the state:

Degree Day and other weather information received from Skybit E-Weather Service: http://www.skybit.com/

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