Southwest Michigan vegetable regional report – August 19, 2015
Aphids and mites have arrived in southwest Michigan.
Weather was again fairly normal for the period with highs from 75 to 89 degrees Fahrenheit and lows from 57 to 68 F. Rainfall was around 0.75 inches. We are near 2,100 base 50 growing degree days (GDD) compared to 1,860 GDD for 2014.
Michigan State University Extension reports aphid numbers are increasing on many crops, with peppers and vine crops being of most concern. Large numbers of aphids on peppers will make the fruit sticky from honeydew. Large numbers also increase the possibility of transmitting virus diseases since aphids serve as the vectors. The virus of primary concern for peppers is cucumber mosaic virus (CMV). High aphid numbers will also lead to transmission of virus in vine crops. Virus of concern in these crops is also CMV, but includes zucchini yellows virus, watermelon mosaic virus and others.
Aphids will generally be on the underside of leaves causing leaves to curl under. Virus symptoms will appear as curled, mottled leaves or bumpy, misshapen fruit. Yellow squash may have green stripes or green bumps. Several summer squash varieties have a certain level of tolerance to many virus diseases and those should be planted for late-season harvest.
Mites have also come on strong over the past two weeks due to the warm, dry weather. Wet weather can keep them under control to a certain extent by rain simply knocking them off the plant. Many crops are susceptible, but two that seem to be favored are tomatoes and watermelon. Look for patches of yellowing plants called “hotspots.” This is where a pregnant female was dropped by the wind, she then laid her eggs and the infestation spread from there. Many control products will require two applications since they may only control adults and not eggs and the second application will control those recently hatched.