This week the fleahopper populations started picking up quite a bit in some of the squaring fields in Wharton county. Even in cotton with three true leaves I was picking up a few fleahoppers. The heaviest population I found was near our fairgrounds, with 18% of plants with fleahoppers present.
The threshold for fleahoppers is 15- 20% present on squaring cotton. I have been finding fleahopper nymphs in fields in all three counties, so they have been present in fields long enough to lay eggs and for the nymphs to go through a couple of molts already.
Hot and dry conditions lately have been favoring another pest that we normally don’t work with very often. Spider mites favor warm, dry weather. Lately we’ve been getting a good bit of that, and in a few places the populations are thriving. They tend to be more common near grassy pastures or ditches, places with drying grass or near dusty margins.
I looked at a field in the blue creek area near El Campo this week with a colony of spider mites on every plant near the edges, and about every third plant all the way to the middle of the field.
The economic threshold for these has not been well studied in cotton, and with cotton this young we tend to keep an eye on it to see if the infestation is bad enough to begin causing defoliation before it warrants treatment. My concern with these arthropods is not just their presence, but that their numbers can be flared if a field is treated with acephate for thrips.
This particular field was approaching the threshold for thrips, there was an average of 1.26 thrips per plant, and the plants were at the 1-2 true leaf stage. We decided to keep an eye on the field for a little longer to avoid causing problems with the spider mites. For more information, go to page 21 of the new Cotton Insect Guide.
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Thrips are still present in smaller cotton in all three counties. The threshold for thrips is 1 per true leaf per plant. Once the plant reaches 5 true leaves, it’s large enough that thrips are no longer a concern.
If you do have a thrips problem, keep an eye out to see if you have spider mites in the field. Treating thrips with acephate can flare spider mite populations. Bifenthrin has some effect on spider mites as well as thrips, but is not normally a first choice for treatment of either pest individually.
I am participating in a study to look at the Bt resistance in cotton bollworms in our area. The study requires me to collect caterpillars out of refuge corn. If you have heavy populations of corn ear worm in your corn, please give me a call.
I found several black swallowtail caterpillars this week near one of the fields I check. They are brightly colored to let predators know they taste bad, and if disturbed they stick out a bright orange structure called an osmeterium from behind the head. It smells awful, but makes them an interesting caterpillar to find. They feed on a variety of plants in the carrot family. For more information, check out this article by the University of Florida.