August 17, 2016 – We have just recorded the first fruit disease infection periods in more than two weeks with the rain that occurred early morning 8/17. So far infections for apple scab, cherry leafspot and black rot in grapes were recorded in Casco and only cherry leafspot at the other weather sites on the peninsula. The rain was not sufficient to alleviate the drought stress currently being experienced in unirrigated fruit plantings. The recent dry hot weather has also contributed to increased mite development and damage in apple and cherry plantings.
Disease Pressure – The length of protectant fungicides application intervals can now be between 2-3 weeks if scab lesions are not present on this year’s leaves or fruit. Captan is the fungicide of choice when protecting fruit from secondary scab infections and storage rots.
Insect Pressure – In orchards where codling moth trap catches remain greater than 5-7 moths per week, additional control applications for this pest should continue on a 10-14 day schedule. Assail, Imidan and Exirel are all good choices for this time of the season. These products will also control apple maggot as it continues to be caught in scouted orchards on the peninsula. If you are not trapping with yellow sticky cards for this pest, it is advisable to begin control treatments on a regular schedule through the end of August.
Trap catches of spotted wing drosophila continue to increase in post-harvest orchards. We expect SWD populations to increase as they begin to infest fruit left in the trees and on the ground. There is no advantage to making control applications at this time. In fact, any controls applied now would likely speed up the development of resistance. The presence of high populations, with the short generation times occurring now, will expose larger numbers of individuals to any materials applied, resulting in greater selection pressure and a greater probability of resistant population development.
Disease Pressure – Evidence of new cherry leafspot infections continues to be minimal. This is likely due to the more frequent application of fungicides along with SWD controls that are being made this season. Post-harvest application of a chlorothalonil fungicide will be important in keeping leaves on the trees as long as possible into the fall.
Insect Pressure – Mite pressure is building in some cherry orchards, especially where pyrethroids were relied on for SWD control. Many miticides are available and control applications may be necessary as stress for this pest during this time of the season can be high.
Disease Pressure – Symptoms of both black rot and phomopsis infection have been observed on grapes here at the Peninsular Station. Grape fruit clusters are now susceptible to infection from powdery mildew, downy mildew, and latent infections of botrytis. Now is the time to apply protectant and systemic fungicides with activity against all of these diseases. As temperatures have increased, powdery mildew and downy mildew control are even more critical.
Insect Pressure – Japanese Beetles and rose chafers have been reported in Door and Kewaunee counties. Click here for more disease and insect information regarding grapes here in NE Wisconsin and around the state from the ‘Wisconsin Fruit News’.