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Field and Forage Crops |
With an early and apparently strong bollworm moth flight now underway in the southern and southeastern counties, twice-a-week scouting is now recommended for approximately the lower half of North Carolina. When the moth flight is underway in their area, in conventional cotton producers should be prepared to respond quickly to threshold levels of eggs, either in the terminals (10 percent) or on square and boll bracts, on white, pink and dried flowers (only 25 eggs). The wetter the weather, the higher the likelihood of eggs being initially deposited mostly in the terminals. Hot, dry weather often results in lower egg deposition.
In B.t. cotton, remember that stink bugs and plants bugs are again likely to be the major boll-damaging pests, even though bollworms becoming established under bloom tags can often cause economic damage. Expect most bollworm establishment to occur under dried blooms stuck to bolls. For bug damage, it makes we recommend carefully inspecting approximately 50 quarter-sized bolls (selected from throughout the field) for internal damage, counting both stained lint and wart-like growths on the inner boll surfaces. This scouting should begin approximately 3.5 weeks after blooming initiation. These quarter-sized bolls may be either cut open with a knife or simply crushed between the thumb and forefinger. An initial threshold of 10 percent internal boll damage is recommended in North Carolina, with the threshold increasing after about 5 weeks of blooming according to the level of large, stink bug-safe bolls (consult either the June 2002 Cotton Insect Scouting Guide or 2002 Cotton Information booklet). Since plant bugs do essentially identical damage to small bolls, all bug damage to bolls is counted together.
Stink bug reports from cotton and other crops have increased during the past week, although it is still too early predict if we are in for another big stink bug year in Bollgard cotton.
Pyrethroids will still be the insecticides of choice for most applications to manage bollworms and stink bugs, although different insect species (such as brown stink bugs, tobacco budworms beet armyworms, fall armyworms and cotton aphids) can dictate the use of other chemicals or combinations.
Recent rainy weather over most of the state should lessen (but not eliminate) populations of spider mites and beet armyworms. On the other hand, a return to hot, dry weather in the coming week may also help bring back these pests, though spider mites seem to have a difficult time becoming established on late July and August cotton. The parasitic aphid fungus, N. fresenii, has begun to occur in a number of counties this past week, which should significantly reduce cotton aphid levels.
Based on this year's heat units, reports from states to our south, and the timing and initial intensity of our major bollworm moth flight, it looks like North Carolina could be for a challenging year for insect management.
Many areas of North Carolina received some welcome rainfall and cooler temperatures in recent days. This helped the peanut plants but was also beneficial in helping with a couple of pest problems. Spider mites had increased in a few areas and were causing problems in several fields. The rain and cooler temperatures were perfect to initiate a rapid spread of a fungal pathogen that kills the mites.
Several scattered locations have suffered from localized infestations of beet armyworms. These caterpillars are not commonly a problem in peanuts, but hot, dry conditions often favor their occurrence. Beet armyworms are more difficult to control than the typical corn earworms we see later in the summer. Hopefully, the recent change in weather will bring this concern to a rapid conclusion. Methomyl (Lannate) is the only labeled insecticide currently listed for beet armyworm management.
Tomato spotted wilt virus is very abundant in a lot of fields. The number of plants that show the typical stunting and ring spot have probably peaked. Later in the summer one may begin to see plants turn yellow and decline. In many instances this is also an indication of tomato spotted wilt virus.
Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Last modified on July 15, 2002 by Stephen J. Toth, Jr.