It has been a cool and wet start to the cotton season in southeast Virginia, and growth is slow. With a slow start to the season some folks are considering a second foliar application for thrips management. There are a couple key things to consider…

The first thing to consider for effective thrips management is timing

The most consistent return on investment comes from a foliar application early in the first true leaf stage. An application at the second leaf stage sometimes pays off, which is more likely to be the case with our current growing conditions. If cotton reaches the three or four-leaf stage, foliar applications made for thrips rarely pay off.

The next consideration is what insecticide to chose.

One of the most commonly used products to control thrips with a foliar spray is acephate. There are two thing to consider when using acephate; 1) western flower thrips are not as susceptible to acephate as tobacco thrips, and 2) acephate resistance has been documented in tobacco thrips in northeastern North Carolina, just across the state line from us in southeastern Virginia.

Populations of western flower thrips have been high so far in southeastern Virginia.

In several trials at the Tidewater AREC in Suffolk, we found around 80% western flower thrips in a foliar insecticide trial. Additionally, collections made from grower fields throughout Suffolk and Southampton counties on May 23 averaged 73% western flower thrips. While most fields did have a majority of western flower thrips, it is important to note that it varies between fields even across a relatively small area, and some sampled fields had a larger proportion of tobacco thrips. A table of thrips collections from May 23 can be found below. Each row represents a sample of five cotton plants in a field in Suffolk or Southhampton county.

Field	Tobacco thrips	Western flower thrips	% Western flower thrips
#1	2	6	75%
#2	2	13	86%
#3	1	4	80%
#4	4	23	85%
#5	11	3	21%
#6	1	9	90%
#7	1	8	88%
#8	4	4	50%

In the foliar insecticide test at the TAREC, acephate (at 3 oz/ac) did not provide better control than not treating with these high populations of flower thrips. Hemi SC (spinetoram), provided good thrips control at both the 2.5 and 3 oz rates. Hemi SC is the same active ingredient found in Radiant and is available for use in Virginia and the Carolinas this year for thrips suppression. It is important to mix Hemi SC with a non-ionic surfactant or with an herbicide which already contains a surfactant, to get good thrips control.

If you are using acephate, you should carefully monitor the performance of the application in your field. If you are not satisfied with the performance of an acephate application, the cotton growth stage and the growing conditions at that time should be assessed before considering a second application. If a second application is made, Hemi SC should be considered for more effective control and to rotate the insecticide mode of action. Bidrin should not be used for a second application after acephate, as these two insecticides are the same mode of action.

Both acephate and spinetoram can be washed away by rain up to 8 hours after application (or possibly longer), but acephate is slightly less susceptible to being washed away when comparing the two. However, some protection from a foliar application is better than none under current conditions, which are expected to extend through this weekend.

As a reminder, if you are planting Thryvon cotton, it provides excellent thrips control and does not need a foliar application. If you have any thrips questions contact Tim Bryant (757-621-8804, btim2@vt.edu), field crop entomologist at the TAREC in Suffolk, VA.