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Field and Forage Crops |
Nothing has changed regarding the earliness or generally large size of the bollworm moth flight during the past week. The flight should spread across the remaining areas of the state in the next few days with, perhaps reaching our northern tier of counties by this weekend or early next week (around July 24), plus or minus a couple of days. High egg levels in the 80 to 100 range per 100 terminals (8 to 10 times the threshold for conventional cotton) were noted as far north as Goldsboro two days ago, and threshold levels of eggs on bloom tags were also noted in several cotton fields on July 21 in Halifax County.
With the generally advanced cotton crop and warm weather, a significant portion of the eggs are being found low in the plants in many fields, particularly associated with bloom tags. Tobacco budworm moths have also been part of the bollworm moth flight in some areas, making control with pyrethroid insecticides more difficult in the early going on conventional cotton. Do not overlook the possibility of bollworm thresholds being triggered by 2 percent eggs deposited on fruit or 3 percent bollworms developing before the egg has met threshold on conventional cotton. Where insecticide treatments with Bidrin, Orthene or Vydate have been made for stink bugs within the past week to 10 days, be aware that the bollworm threshold will likely be met quickly on both conventional and on Bollgard cotton. For a review of threshold, see the Cotton Insect Scouting Guide.
Stink bugs have continued to cause headaches for growers across much of the state. A stink bug threshold study in Wayne County had 40 percent internally-damaged bolls in untreated Bollgard II cotton on July 22. The dirty bloom level was 5 percent (only a third of the 15 percent plant bug threshold), so this damage was caused mostly by stink bugs. Although this damage was much higher than most reports received by our office during the past week, damage levels like this illustrate the importance of monitoring internal boll damage. At least half of the adult stink bugs reported in most cases are the brown species, pointing toward the possible need for a pyrethroid tank mix with one of the stink bug insecticides. The potentially high damage to bolls during the next few weeks should be taken very seriously by growers. On the bright side, a few areas of the state have experienced only light to moderate bug damage. We would still recommend staying with the protective 10 percent internal boll damage threshold for the initial four weeks of blooming.
Fall armyworms also have the potential to cause boll damage in the coming days and weeks, though not over wide areas. Unfortunately, no insecticides provide good control of one-third to one-half grown fall armyworms. A number of insecticides, such as Larvin, Steward, Tracer, Intrepid and Denim, provide fair to good control of small fall armyworms, and a few pyrethroid insecticides, such as Capture and Karate, appear somewhat more effective than others in keeping fall armyworms from becoming established. In the past, we have had fair to good success with a pyrethroid insecticide plus Larvin tank mix; however, we have had very little experience with the newer insecticides noted above. Although Bollgard cotton is not known for its activity on fall armyworms, in the past fall armyworm levels and damage have been somewhat lower on Bollgard than on conventional cotton. Bollgard II cotton is resistant to all caterpillar species, except for some cutworm species.
With our rapidly maturing crop, the susceptibility of cotton to late season insects should lessen significantly within the next few weeks, with some cotton fields beginning to cut out already. In the coming two weeks at least, however, it would pay to be vigilant and respond quickly to threshold levels of bugs and caterpillars.
Peanuts are doing fairly well this year with regard to insect pest problems. Potato leafhoppers have been sporadic and some growers have opted to add an insecticide into the leafspot spray if leafhopper injury was present on 25 percent or more of the leaflets. Despite some areas having plenty or rain earlier in the summer, spider mites do still pose a threat this summer. The hot temperatures of the past few weeks combined with warm temperatures early in the spring have made it possible for spider mites to cause a few problems this year, so stay alert for these pests.
It will soon be time for caterpillars to occur in peanuts and while the threat for this year is uncertain, it does appear that fall armyworms may be more of a threat than normal. Refer to the 2004 North Carolina Agricultural Chemicals Manual for recommendations on the control of fall armyworm as this caterpillar is a little harder to control than some of the others. Fall armyworms typically do not cause as much damage per individual as corn earworms. Therefore, the threshold for treatment should be increased to at least 6 and up to 8 per row foot. If you do spray for caterpillars, remember that foliar sprays can increase the likelihood of spider mites, so you will need to watch for them in the weeks following a spray.
Tomato spotted wilt virus symptoms have increased over the past two weeks due primarily to the hot weather. There are plants that are already infected, but had not shown symptoms until stressed by the hot weather. Remember that the application of a foliar insecticides for thrips control at this time of year will not offer any benefits for tomato spotted wilt virus suppression.
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 26, 2004 by Stephen J. Toth, Jr.
