This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, ctrostle@ag.tamu.edu
High Plains
Threshold is Lowered for Triggering Sugarcane Aphid Sprays
The following was published Friday, August 14, by Dr. Pat Porter, Extension entomologist, Lubbock. The full story is on the main page at http://txscan.blogspot.com/ (scroll down for August 14).
“Now that we have had a few weeks of experience with field-scale sugarcane aphid control in the southern High Plains, it appears we need to move to a more conservative treatment threshold than the one currently in use. What we are finding in commercial fields and our insecticide trial is that our insecticides do not seem to be working quite as well as they do in more southern locations with higher humidity and less intense sunlight. Whether our environment affects the insects, plants and/or insecticides differently is unknown, and what we are seeing could be a combination of all three factors – or two or one or none, we just don’t know. Insecticide coverage issues may also be in play. We could be experiencing insecticide interception by excessive honeydew such that some of the insecticide never gets to the leaf surface. We also do not know the importance of reduction in coverage and canopy penetration attributable to aerial application rather than ground application with higher volumes of water. Additionally, we also have reports of narrow row fields (less than 36 inches) having reduced insecticide efficacy, and this of course is a coverage issue.
The preceding paragraph is basically to say that we are not sure what is causing reduced control. We want to make it absolutely clear that there is no reason to think this is a resistance issue. However, with regard to application timing the prudent thing to do is to initiate insecticide applications sooner, before the aphids reach 50-125 aphids per leaf. For that reason we are recommending the action thresholds in use in Mississippi.”
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Consult the above URL for the full report. Thresholds have been changed from 50-125 average aphids per plant to a percent infested plants (20% or 30% depending on growth stage). Furthermore, some additives may be considered to potentially enhance insecticide effectiveness. I have also heard reports of suggestions to increase insecticide rates (now possibly 1.5 oz/A for Transform, up from 1.0; and 5.0 oz./A for Sivanto, up from 4.0). Do not overlook the importance of coverage—which requires higher gallonage, closer spraying to the target (airplanes flying too high?), etc. –Calvin Trostle
