Wednesday, August 5, 2020

Cotton Insect Control for Remainder of 2020 Season

In most seasons, we would be entering the home stretch for cotton insect control by early August. While this may be true for fields planted on time in 2020, it is not the case for a lot of late planted, late emerging, late maturing fields this season. I hope we can narrow our focus to just a few species of insects for the remainder of this season. The primary group would be the bug complex (plant bugs, stink bugs, and leaf footed bugs). However, there are several other insects that could arise if weather conditions or other circumstances permit. These are spider mites, late season aphids and especially silverleaf whiteflies.

The insects of focus for the remainder of the 2020 season may not be as concerning as how long our management and control programs should extend into September and even October on our later maturing cotton. Let’s look at some general guidelines. If past seasons give us any trends, our escape bollworm issues should end by Labor Day. However, we should continue our monitoring as long as our late maturing fields have squares in the top of plants that would serve as a food source for a one-day old bollworm. Once all the squares are gone, escape bollworms will have a difficult time becoming established. The bug complex should eventually be dominated by stink bugs here in Alabama. This may consist of several species; the brown, southern green, leaf footed bug, and the brown marmorated (BMSB), which can now be found in many cotton growing counties. How long should we continue stink bug controls on late maturing cotton? Our general rule with our traditional stink bug species is to continue controls until the top bolls we hope to harvest are about 25 days old. When the BMSB is in the mix, we may need to protect even longer since this species will attack bolls from thumb nail size, up until they begin cracking. With our late maturing fields this season, we will need stink bug controls through at least the month of October. An application for stink bugs usually gives us 10-14 days of boll protection. However, as some fields mature out, just like with corn, stink bugs will move to younger cotton, or swag areas of fields that are still producing bolls or to late maturing soybeans. In other words, as our crops mature in September and October we will get field to field and crop to crop movement of stink bugs. As far as insecticide choices—Bidrin, bifenthrin or any other pyrethroid at a high-labelled rate should give adequate control. The best way to scout for stink bugs will be to examine bolls for internal injury. Just observing or using a sweep net or drop cloth for stink bugs is not very effective and often leads to underestimating the number present.