West Texas Cotton: Scout for Aphids and Bollworms

Suhas Vyavhare, Extension Cotton Entomologist, Texas A&M AgriLife Extension Service


Cotton will benefit from some of the timely rainfall we have been receiving recently. However, it is going to make conditions better for survival and multiplication of several pest species as well. In general, the hot and dry weather of West Texas helps to keep bollworm numbers in check (through desiccation of eggs). Humid and cloudy conditions over the last couple of weeks, however, may increase egg hatch rate and worm survival in cotton. In addition, added new growth on plant terminals will help both bollworms and aphids thrive better.

Over the last 10 days, we have spotted many fields with cotton aphid infestations. Aphid colonies are mainly concentrated to plant terminals but as the numbers build-up, they may move on to the leaves. Overall, beneficial numbers seem to be lower compared to the previous year, but they are present. Isolated showers will also help wash out honeydew and some of the aphids from the plants. If aphid colonies are spotty and mostly restricted to plant terminals, I would wait and monitor the situation over the next few days. Often aphid populations crash out in response to beneficials and rain. Click the link below to access more detailed information on cotton aphids: http://lubbock.tamu.edu/files/2017/07/Cotton-aphid_ENTO074.pdf

I have also come across a few reports of bollworm damage to non-Bt cotton. In our research trials, bollworm damage ranges from 5-6% boll injury in non-Bt cotton and <1% in Bt cotton. The threshold is 6% fruit injury with the presence of live worms in both Bt and non-Bt crop. Among various insecticide options for bollworm control, Diamide insecticides (Prevathon and Besiege) are the most reliable choices. Remember, Besiege contains both a diamide and a pyrethroid so it would be a better choice if stink bugs are present too. However, if aphid colonies are present in the field, the pyrethroid component may flare-up aphids. If a field needs to be treated for both aphids and bollworms, Prevathon can be tank-mixed with any of the commonly used aphidicides such as acetamiprid (Intruder).

Along with the proper insecticide selection, coverage is also important getting the desired level of worm control. In fields with dense plant canopy, it is important to get material down in the lower canopy where worms are in protected places.  Air induction nozzles recommended for newer herbicide technologies produce coarser spray which may not penetrate through the dense plant canopy and provide thorough coverage. Penetration through plant canopy can be improved with flat fans or hollow cone tips and byincreasing final volume (no less than 10 GPA with a preference of 15 GPA for ground rig). If using an airplane, use at least 5 GPA. 

Comments

Post a Comment

Popular posts from this blog

Assessing the Value of Bt Corn When Insects Are Resistant - Part I: Corn Rootworm

Image
We are entering a time when insects have become resistant to many of the Bt toxins in our GMO corn and cotton. This is the first in a series of articles where I will discuss what this might mean in terms of crop damage and the value of the Bt technologies.  To start the series, I want to make it clear that Bt crops are more than just insect protection; they are herbicide tolerance, cold tolerance, and improved genetics for yield, drought and disease tolerance. These other virtues remain even when the insect control fails, although reduced insect control clearly can affect some of them, like yield potential and drought tolerance.  Back in the early days of Bt crops, seed companies defined and charged a "technology fee" that was added to seed cost; growers knew what they were paying for insect protection. Those days are long gone, for various reasons, and now the seed cost is what it is and there is no way to know how much is being paid for the Bt traits.  While we don't kn...
Read more

Soldier Beetles, Not Blister Beetles

Image
A Lubbock County grower came to my office this morning with a bottle that held 20 or so beetles he collected from the edge of a field. His concern was that they were blister beetles, and I was pleased to be able to say that they were soldier beetles. However, given the high numbers he described in the field, soldier beetles must be very abundant this year. Photo credits: Ed Bynum and Pat Porter There is some resemblance, but these beetles are different enough to be separated on sight. One problem though is that he showed me a web page that incorrectly identified soldier beetles as blister beetles; the internet strikes again. Texas growers can always send us a photo of an insect if they want an identification. Soldier beetles, insect Family Cantharidae, are predacious on other insects as both adults and larvae. Blister beetle larvae, insect Family Meloidae, are predacious on grasshopper eggs and the larvae of wild bees. When disturbed, blister beetles exude hemolymph (the insect versio...
Read more