Friday, September 29, 2017

SCA After the Rains: Now What?

We are now concluding five straight days of rain on the southern High Plains, but sugarcane aphids are still with us. I spent some time today collecting infested leaves and examining the aphids under a microscope, and I have to report that I can't find any evidence of the fungi that hammered populations on the Gulf Coast. (Although I will keep monitoring the situation.) Most of the aphid colonies I observed looked just fine, and there were some beneficial insects like syrphid fly and lady beetle larvae feeding on them. Dr. Katelyn Kesheimer, IPM Agent in Lubbock and Crosby counties, took 7 Day After Treatment data in a sugarcane aphid efficacy trial yesterday between rain events, and she reported that there was a slight decrease in aphid numbers on the untreated plots, but nothing to write home about.

So the rains did not really reduce the number of aphids, but, significantly, the cooler temperatures slowed them down. Aphid development and reproduction is slower in cooler temperatures, so the explosive population growth potential is not going to be here until we get significantly warmer. The practical effect of this is that fields that still require treatment, or will require treatment, do not have to be sprayed as quickly as they would be in hotter conditions. This is good for a few reasons, one of which is that it will pay to wait a few days.

We know that our insecticides do not work as well when it is cold, or, put another way, they work better when it is warm. Current predictions put the warmest days next week as Sunday - Tuesday, and then Friday - Sunday. If an application needs to be made, make it during the window of warmest days. Given that we don't really have hot weather in the forecast, it would not be a good idea to cut insecticide rates in the face of these moderate temperatures.

Dr. Kesheimer included a generic formulation of imidacloprid in her efficacy trial because growers are using it due mostly to its relatively low cost and a marketing push. We already have older data that this off-label insecticide does not provide good sugarcane aphid control, and her 7DAT data are reinforcing what we already know. Transform and Sivanto remain the effective sugarcane aphid insecticides.