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Late Season Cotton Insect Considerations
This is Jack Bacheler, Extension Entomologist at NCSU with the Wednesday Cotton Insect Update. Today is Wednesday, August 10.
At this time of year, as most cotton has become increasingly mature and unattractive to stink bugs and bollworm moths, other cotton which was either planted late or was lucky enough to have received good rainfall, and is still producing and setting young fruit, may fall victim to high levels of these insects. These insects pests are able to seek out and concentrate in the remaining attractive cotton fields.
Even in still attractive and susceptible cotton fields, in the case of stink bugs, if the producer has kept up with the date of first flower, the dynamic threshold can serve as a guide to raising the damage threshold accordingly at this time of year, using a threshold of 20, 30 and 50% internal damage to quarter-sized bolls for weeks of 6, 7, and 8 of the bloom period. Another option late in the season is to use the ruler on the stink bug field card to assess the diameters of first position bolls. If 80% of the first position bolls are larger than 1¼ inches in diameter, these bolls can no longer be damaged by stink bugs and the threshold could be at least raised 5-fold from the protective 10% level to 50%. If the latter approach is used, disregard the small, slow-growing bolls in the upper 2 to 3 nodes of the plant.
With bollworms, most consultants continue to use common sense during the latter part of the growing season. In cases in which most bolls are hard and spotted, the threshold of 3 second stage or larger bollworms per 100 fruit could probably be safely raised to 8 to 10% live worms. Be careful of the fields that are still attractive and have a moderate to high number of younger bolls, however. The lower threshold is more appropriate here. This also seems to be an exceptional year for high levels of bolls which have kept their dried blooms. So be sure to include bloom tagged bolls in your sampling.
Although we have seen spider mites in a number of fields this past week, levels were on the low side and the odds of economic damage at this time of year are getting slim.
As has been the case essentially all summer, most areas of the state could stand additional rainfall for the next few weeks to help fill out bolls.
I guess that’s about it for this week. See you next Wednesday on August 17. See you then.