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This is Jack Bacheler, Extension Entomologist at NCSU with the Thursday Cotton Insect Update. Today is Thursday, July 10.
Today seems to be about the point at which just over half of our cotton is now blooming; so it’s fair to say we are probably getting close to our long term maturity average. Generally, our moisture situation is much better than a week ago, but some of our cotton acreage has still managed to escape the thunderstorms.
Spider mites continue to be a localized concern, although some populations have declined during the past week, probably due to a parasitic fungus. Significant rainfall in some areas of the state has helped this fungus along and also greatly lessened plant stress. Relatively few cotton fields have been treated so far this year for spider mites, although low level populations seem to be present in many areas. So some potential for mite buildups exists. Scouts should definitely be on the alert for mites in the coming days and weeks. In some parts of the cotton belt, when mites reach a certain levels, sometimes scored by counting mites on a defined set of leaves, spraying is advised due to the high probability economic damage in the coming days. In North Carolina, with our generally high humidity and associated fungal pathogen, assessing levels in this manner would likely result in unneeded spraying. However, when mite populations are present on at least 25% of the plants in a large area of the field and some lower leaves have turned yellow and dropped, treatment probably pays unless rain is expected. As we mentioned last week, significant rainfall can be a real blessing in reducing mite levels, so delay the application and reevaluate 3-4 days after the rain.
Plant bugs still seem to be present at higher levels across the state than in recent years, and we still are receiving scattered reports of fields being treated for these pests, similar to last week. Our project’s situation in a spider mite and plant bug test in Wayne County this past Tuesday, July 8, sounds similar to the experience several others who have called in. On the mite end of things, the yellowish leaf stippling was obvious throughout much of the field in our test with some leaf reddening present, but mite levels were only low to moderate, and no or only limited lower leaf drop was evident. With plant bugs, the adults were certainly in evidence, but sweeping revealed an average of approximately 3-6 per 100 sweeps and upper square retention was in the range of 90%, when we inspected one terminal square and one lateral square two nodes down from the terminal. Most square loss was occurring 2-3 nodes down from the terminal, so don’t overlook this common plant bug target area.
Although things could change, particularly in areas which have received adequate moisture levels, consultants have reported low cotton aphid levels so far this season. However, the next 3-4 weeks are often our most likely time period for treatable levels of cotton aphids, so scouts should report any cotton aphid observations that show the characteristic upper terminal wilting from aphids, especially if these symptoms are widespread. Scouts should also recognize and report items such as aphid mummies, the parasitic fungus, and the moisture status of cotton plants. Aphid infestations only rarely cause an economic loss to SE cotton that is not under moisture stress.
We’ll provide three additional cotton scouting schools in Halifax County, Northampton and Halifax counties during the week of July 21 to 25. More on those next week.
Hopefully, we’ll keep getting these late afternoon thunderstorms across more of the state in the coming week. See you next Thursday on July 17 for our next cotton insect update.