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This is Jack Bacheler, Extension Entomologist at NCSU with the Cotton Insect Update. Today is Thursday, June 13.
Our recent extended period of adequate to excessive moisture levels, continued plant cotton development and lower migrating thrips levels have probably pushed thrips out of the picture for all but a very few cotton producers. With most possible cotton insect pest problems other than thrips still on the horizon, maybe we can take a stab at what to expect in the coming weeks or months.
As mentioned last week, we sure have an abundance of moisture-enhanced plant bug host material out there as many weed and even cultivated plants qualify as hosts for this pest. It will be interesting to see if a possible rapid host dry down in the coming weeks leaves cotton plants as a nice go-to host this growing season. Most producers, consultants and scouts in both the Southeast and the Midsouth have confidence in the 80% or greater upper young square retention guideline as an indication that cotton plants are safe from plant bug damage for the next 5 -7 days, and that for cases of less than 80% retention, sweep net sampling is needed to detect the presence of damaging levels of plant bugs. Recognizing downward trends in square retention from one week to the next can also help in anticipating upcoming plant bug issues. An 8 or more plant bug level per 100 sweeps is often used as treatment threshold in the Southeast in cases of low square retention. We’ll talk more about sampling for plant bugs after bloom initiation with ground cloths in the coming weeks. The key with much of our insect management advice is to get out these and look at cotton fields regularly and to use suggested thresholds for treatment decisions.
We appear to have huge populations of brown stink bugs in the state so far this year, with many recently coming off of mature and even harvested wheat, weed hosts and other plants. In the case of field corn, some infestations in the zone of newly-developing corn ears already appear to be significant. In the case of cotton, about all we can say is that we have the potential for very high levels at this point. On the plus side, we typically do not find significant stink bug damage to bolls until after about the second week of bloom. If the weather turns dry between now and the first or second week of bloom and negatively impacts cotton growth, potential damage to cotton bolls could drop significantly. However, at this point, 2012 reminds me of our Year of the Stink Bug in NC 2004 when we averaged just under 15% boll damage from stink bugs averaged across the state, as opposed to our longer term average of 3 to 4% boll damage under grower conditions. Remember, however, that percent damaged boll figures for stink bugs do not equate to as high a level of yield loss as with bollworms. Unlike bollworms which more often than not damage the whole boll, stink bugs damage a variable number of boll locks, ranging from complete boll damage to no boll damage. We’ll have much more on stink bugs in the coming weeks as the season unfolds.
In North Carolina, we also often seem to have more reports of cotton aphid infestations during wetter weather. However, in tests conducted here and elsewhere in the Southeast, we have very few cases of yield losses resulting from cotton aphid infestations if adequate or excessive moisture levels exist. Yield losses from cotton aphids primarily result from large populations throughout fields that then become economic infestations when cotton dries down quickly and the subsequent moisture stress adds to the similar stress caused by aphid feeding. And, more often than not here, aphid mummy parasitoids and a parasitic fungus come to the rescue.
That’s about it for this week. We’ll talk to you again next week, hopefully on June 20.