From: Jack S. Bacheler
Spider Mite Outbreaks
This is Jack Bacheler, Extension Entomologist at North Carolina State University with the Cotton Insect Update. It's Wednesday, June 15.
This past week's heat and dry weather appear to have contributed to widely scattered two-spotted spider mite outbreaks, some at treatable levels. A high proportion of these early infestations that I have seen first hand have been almost randomly scattered in cotton fields or present through the whole field, as opposed to the field edge invasions more common later in the season. Control with insecticides at this early stage appears to vary, with several cotton fields essentially devoid of medium and adult mites, but with large numbers of eggs and a few very small, recently hatched mites 3-4 days after application. Results like this may be indicative of the need for a second application if mite conditions persist.
When inspecting plants for spider mites and the possible presence of the fungus, a hand lens is indispensable. If mites are present, just focus the hand lends on the undersides of a speckled leaf. Unlike cotton aphids, mites tend to be active crawlers, and their small pearlish very round eggs (not unlike cotton pollen) are easy to spot with magnification. If an active mite population is widespread in a cotton field and lower leaves have begun to drop, treatment may be in order. Hold off, however, if rainfall is predicted, or if the fungal parasite is present. Control with one of the five insecticides listed in the 2005 Agricultural Chemicals Manual may vary from marginal to good, but is often closer to the marginal side. With this pest, ground equipment is a better option than air, as volume the 20+ GPA, hollow cone nozzles, and high pressure are recommended. A newly labeled miticide, Oberon (spiromesifen) from Bayer is now available, though activity here awaits more thorough testing.
As of this June 15 writing, an inch or two inches of rainfall across much of our state would be just the ticket to help bring on the parasitic mite fungus and reinvigorate cotton growth.
Although it's still on the early side for plant bug and stink bug predictions, both pests appear to have the potential to be a problem again this year based on early sampling of alternative hosts. Stink bugs are typically the most worrisome of the three, but they cannot impact cotton until after blooming and boll formation has begun. Indirect assessments for plant bugs begin with the monitoring of square retention. Once squaring begins, unless plant bugs intervene, square retention is often in the mid to high 90's here until approximately the first or second week of blooming. If the square retention rates drop below 80%, further assessments with a sweep net are advised as outlined in the Cotton Information booklet.
Cotton aphids are again present in quite a few cotton fields, though presently at very low levels.
We'll try to keep you up to date on the general cotton insect situation for the remainder of the growing season. See you next Wednesday, June 15.