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This is Jack Bacheler at NCSU with the Wednesday Cotton Insect Update.

On the insect front, in general this is the time of the growing season when insect problems at a low ebb. Very little of our cotton is less than the three true leaf stage and some is beginning to square. Cotton that has not already grown beyond the thrips-safe 4-5 true leaf stage will soon be there, especially with the recent June 9 rainfall over much of the state.

From now until bloom initiation when our attention turns to stink bugs, cotton aphids, spider mites and plant bugs are the three cotton pests that have the potential to cause economic damage. Fortunately, in an average year we typically do not exceed more than 5% of our cotton acreage being treated for any one of these pests. However, state averages and long odds don’t mean much if you are the producer with a cotton aphid, plant bug or spider mite problem.

The Extension Director in Chowan County reported that some fields had significant mite levels on cotton seedlings that seem to coincide with a long dry spell that ended recently. The initial part of scouting for spider mites is easy because we’re looking for infestations that in North Carolina need to reach high levels before a foliar spray is justified. Generally, though not always, mites are more likely develop on cotton during extended hot dry weather and following seed treatments. Also in reduced tillage cotton, mites can more commonly become established throughout cotton fields as opposed to along field edges of conventional till cotton adjacent to recently mowed road rights of way, ditch banks, etc. As a general rule of thumb, it may pay to treat for spider mites if more than half of the plants are infested to the point of beginning to drop yellowing bottom leaves. Spraying can be postponed or eliminated if significant rainfall is predicted as this greatly increases the odds of the mites being reduced or eliminated by a pathogenic fungus in the same genus (species group) that attacks the cotton aphid. Control during hot dry weather is sometimes only marginal. High volume and pressure (good coverage to bottom leaves) is typically needed for good control of spider mites. Flagging some spots in a field where mites are present and returning in 3-5 days is one method of assessing if the mite population is increasing. Also, the detection of large numbers of very round eggs on the lower leaf surfaces with a hand lens is another way to recognize a building mite population.

Cotton aphid outbreaks are 2 to 12 times more likely following a seed treatment than following Temik. Like spider mites, before treatment is justified, cotton aphids should be present on most cotton plants in a cotton field with plants showing significant wilting and the presence of widespread honey dew on drought-stressed plants. Fortunately, due to our high humidity and low spray environment, cotton aphid outbreaks are usually contained by two species of parasitic wasp larvae that result in aphid mummies and by the parasitic fungus Neozygites fresenii that can reduce of eliminate aphids over wide areas. The fungus most commonly comes to our rescue during the third or forth week in July and can be extremely effective.

And finally, because NC cotton fields have a low probability of needing treatment for plant bugs, intensive assessments with sweep net or beat cloth can often be ruled out by a determination of upper square retention. If square retention is above 80%, further scouting for live plant bug adults and nymphs is not need at that time. In NC upper square retention is commonly in the mid-90’s 3 to 4 weeks into the bloom period.

More detailed information about the biology and management of spider mites, cotton aphids and plant bugs is available in Chapter 11 of the Cotton Information Booklet or at our Cotton Insect Corner website which is easily “Googled”

Well, that’s it for this week. See you next week on June 18. See you then.