Managing Cotton Aphids in 2014

We had a few calls over the last week about poor control of cotton aphid with Transform. In all of those cases, the field was actually sprayed for plant bugs with a 1.5 oz rate of Transform. That rate should be very effective on cotton aphid based on previous experience. As a result, we collected aphids from three different fields this week to test their susceptibility to Transform. Based on bioassays that we did with those aphids in the lab, all of those populations appeared to still be susceptible to Transform.  We  are still a little puzzled about what happened, but we have a few ideas.

As you know, temperatures last week were unseasonably low for late July in Mississippi. Additionally, we had rainfall totals that ranged to well over 4 inches in some areas. In all cases, the application went out just before the weather changed. We feel that the weather played an important role with poor control. In all cases, the spray was out well before the rain started and we don’t feel like that played a big role.

The cooler weather was most likely the factor that impacted the performance of Transform. Generally we are controlling cotton aphids when daytime temperatures are well into the 90’s and everything moves fast. When we have temperatures in the lower 60’s at night and low 80’s during the day with cloudy skies, everything just kind of slows down. The plants are not actively growing at a fast rate because heat unit accumulation is low, the aphids become less active and are not aggressively feeding. All of this affects the ability of a systemic insecticide like Transform to move into the plant and be ingested by aphids where it can work.

Over the last couple of days, we have looked at several cotton fields where aphids were sprayed with Transform. We looked at one of the  fields that we collected aphids from this afternoon. The field was re-sprayed with 1.5 oz of Transform Tuesday. After 3 days, control could be characterized as very good. This situation is not something that we will encounter very often, but it is something to be aware of if we are treating aphids with any systemic insecticide when conditions are less than ideal for cotton growth and development.