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Field and Forage Crops |
We can now count on the major bollworm moth flight being both early and high (perhaps very high) throughout much of North Carolina. Even as early as this past Monday, July 15, one of the light traps in Robeson County captured almost 600 moths in a single night. More recently this trap caught 720 moths in a single night. Others traps in Duplin, Sampson, Bladen, Lenoir, Jones, Craven and Onslow counties have shown enough of an increase to confirm the presence of the bollworm flight in this region. By this coming week (July 22-28) these flights will likely be underway throughout the state. In a few of the northeastern counties, Dr. John Van Duyn, Extension Entomologist, Vernon James Center, Plymouth, North Carolina, has reported some instances of tobacco budworms becoming established earlier than bollworms. This situation can result in low, but possibly economically-damaging, levels of budworm larvae becoming established prior to the bollworm flight. For this and similar situations, a 3 percent larval threshold in blooming cotton is recommended prior to the arrival of the major bollworm moth flight.
In the vast majority of cases, however, this early and strong bollworm moth flight will trigger initial pyrethroid application(s) based on the egg threshold. An aggressive response to threshold levels of eggs (10 percent in terminals or 2 percent on fruit) with medium to high rates of pyrethroids is recommended for most situations where reasonable yield expectations exist. Generally, expect bollworm eggs to be deposited on fruit and stems within the canopy in dry weather. Even in cases of good moisture, many eggs are being deposited down in the plants. In both conventional and in B.t. cotton, give particular attention to eggs deposited on fruit (particularly dried blooms stuck to small bolls) and stems. This is shaping up to be very tough bollworm year.
We also have a significant amount of short, drought-stressed cotton which has been blooming out the top and will shed fruit upon the arrival of the first significant rainfall. Because yield expectations are considerably lower in this situation and because the fruit most readily shed is small, bollworm-susceptible bolls, decisions about the amount of money spent for bollworm control are more difficult. Even in these situations, one or two well-timed pyrethroid applications will typically more than pay for themselves.
Although few serious aphid outbreaks have been reported, low to moderate levels of cotton aphids are in an exceptionally high percentage of cotton fields at this time. Thus the potential for aphid outbreaks remains high. On the other hand, levels of beneficial insects such as ladybird beetles and mummifying wasp parasites are providing significant help in reducing these populations in some fields, and the aphid-destroying fungus, Neozygites fresenii, has now been reported from several areas of the state. It will be interesting to see if the fungus can hold aphids to sub-treatment levels in the coming weeks. Some insecticide treatments for cotton aphids are underway, with the new materials (Trimax, Centric and Intruder) generally providing good to excellent control. I recommend holding off cotton aphid treatments unless aphids are present throughout the field, a significant level of terminal wilting is observed, honey dew is widespread throughout the field, little or no aphid mortality from the aphid fungus is present, and the cotton is stressed. In two aphids tests in Scotland County evaluated this past Thursday, July 18, all of the above three insecticides provided good to excellent aphid control.
Scattered significant levels of beet armyworms have been reported again this past week from widely varying locations in North Carolina, ranging from Chowan County in the Northeast to Scotland County in the southern Sand Hills. Some of these infestations are high enough to warrant insecticide treatment. The point at which treatment is justified is difficult to judge, and the old threshold of 5 hits per 100 row feet was essentially established to declare exemptions for the use of unregistered insecticides for beet armyworms under Section 18 Emergency Exemptions. Perhaps a better threshold might be about 10 percent beet armyworms feeding on squares and small bolls (or their bracts) with beet armyworms relatively easy to find in white blooms (25 percent or more). Producers have had good results with low rates of Tracer insecticide with earlier infestations, but some have reported relatively poor beet armyworm control this past week with low and medium rates. This relatively poor control is puzzling, but perhaps due to different populations having differing tolerance to insecticides. At this point, Intrepid insecticide at the 4.0 ounces per acre rate is probably a better choice. Steward also has beet armyworm activity, but less is known about this product. Beet armyworm outbreaks have the potential to become far more widespread in the coming weeks, particularly if the hot, dry weather continues on a significant portion of the cotton acreage. A tropical depression's worth of rainfall is badly needed.
Look for the new labeling for Steward insecticide for use on peanuts. This product is effective against earworms, fall armyworms and beet armyworms in peanuts. You should see information on this insecticide soon, once all of the state labeling is complete.
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 22, 2002 by Stephen J. Toth, Jr.