Wednesday, September 19, 2018

Late season aphids

    After a week of above average temperatures, our pecan trees seem to be infested with aphids and covered in honeydew (photo at right). Every surface of every leaf is sticky with honeydew and numerous flies and wasps are busy collecting the sugary substance.
    We seem to get a late season aphid outbreak almost every year and I usually recommend not trying to control these insects because the cure often increases the problem in the long run.
   One interesting observation I've made about aphids this year is how weather conditions can influence their populations. Back on August 13th I photographed the first aphids I found (photo at left). At that time, the population of black-margined pecan aphids had reached high enough numbers where you could easily spot drops of honey dew on the leaves. But then the weather changed and we received more than 7 inches of rain over a 5 day period. Both the honeydew and most of the aphids disappeared, washed from the leaves by the heavy rain.

    The weather dried out over the next week and I noticed just a few aphids on the underside of  the leaves of my pecan trees (photo at right).  But then the clouds rolled in again and dumped enough rain to cause localized flooding. The heavy rain was again enough to knock down the aphid population.
   Over the past two weeks, the weather has been dry and unseasonably hot. And now we have an explosion in aphid populations (photo at left). Every leaflet seems to have at least a dozen aphids feeding on the sap of the pecan tree.
   A large aphid population usually crashes on its own but the rain predicted for this weekend may serve to hasten the crash.
   I certainly hope we get enough rain to wash the foliage clean of honeydew and aphids. Lately, I've been getting covered in honeydew as I collect nut samples from the pecan breeding project. Its driving me crazy to get sticky plant sap stuck in my hair.