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The information and recommendations in this newsletter are applicable to
North Carolina and may not apply in other areas.
The bollworm moth flight was variable this past week, but for the most part remained high across much of North Carolina. Trap counts have increased in parts of our northern counties now. A light trap in Chowan County had a two-night catch of over 500 bollworm moths on the morning of July 24. Next door in Bertie County the Woodard trap contained approximately 400 moths (two-night catch), and the Hobgood trap in Halifax jumped to 177 earlier in the week. These catches indicate that even the northern-most counties in the state have probably reached, or will shortly reach, the egg threshold. The western Piedmont (Anson, Stanley, Union, Montgomery, and Richmond counties) traps, some in the 100 to 200 range since Monday, indicated that the flight is also well underway in that area. Traps in the central, southern and southeastern portions of the state remain high, although some appear to be trending downward slightly. However, egg counts in the Florence, South Carolina area (approximately 40 miles south of the North Carolina/South Carolina border) are still in the 100+ range in some fields. I continue to see fields in the range of 100 or more eggs per 100 terminals. I also still expect this year's flight to stay for quite a while. Bollworm control to this point has been good, although continued respect for this large flight is warranted. Tobacco budworm moth levels have increased in a number of areas in the past week and will begin occurring as a part of the caterpillar population along with bollworms. Because even pyrethroid-susceptible budworms are more difficult to kill with pyrethroids, a strict adherence to sound scouting and thresholds is important.
With the high levels of bollworm moths and the potential for moderate damage to B.t. cotton, producers should be encouraged to follow a close scouting schedule and to utilize suggested treatment thresholds, as opposed to preconceptions of the degree of protection this technology may or may not provide. In a number of fields of B.t. cotton, producers will likely experience higher levels of stink bugs and plant bugs than in past two years. Plant bug damage to post-blooming cotton is most easily noticed by the presence of "dirty blooms", caused by plant bug feeding on squares; one dirty bloom per 3 to 4 plants indicates the need to sample further for plant bugs. Finding small, darkened squares in the terminals with no evidence of bollworms points to plant bugs as the most likely culprit. The main damage caused by plant bugs in the later-stage cotton is to small bolls. As is the case with stink bugs, internal damage must be confirmed by slicing open these bolls with a knife and examining the internal area. As with stink bug damage, an economically-damaged boll will have stained developing lint, varying in color from pale yellow (new damage) to dark brown and extensive. Suggested thresholds for this damage are: 1) 5 percent internally-damaged small bolls (can be added to the similar stink bug damage); or 2) a careful visual inspection yielding 15 plant bugs (including large nymphs) per 100 plants. Stink bug external damage to bolls is similar to plant bugs, except that the damage spots are larger and usually sunken, while the smaller plant bug feeding spots are typically smaller and look metallic in sunlight.
Although the most commonly met bollworm threshold on B.t. cotton is 3 percent larvae 1/8 inch or larger in size, a few Bollgard fields have met the conditional 100 eggs per 100 terminals or 20 eggs per 100 fruit threshold. If treating at this high egg threshold, do not make any subsequent applications at the high egg threshold unless at least 10 days has elapsed. High egg levels may continue after an insecticide application has been made, with the insecticide continuing to provide excellent control of hatching and young bollworms until the residue has eroded to a low level. A better option following an egg threshold treatment to B.t. cotton would be to return to the 3 percent larval threshold.
European corn borer moths seem to be increasing in some areas, but are very low in others. Scouts and producers should first look for cotton plant stem tunneling and wilting of the plant tissue above the feeding site. The sawdust-like "frass" is also a good indication that the damage is the result of European corn borer tunneling. Flushing European corn borer moths from around cotton fields and presence of these feeding signs could indicate a field which may be in need of additional protection (see the July 17 issue of the "North Carolina Pest News").
A very high level of all stages of beet armyworm was found by Ann Evans, a cotton producer's wife, in a 50-acre field of conventional cotton in Nash County. Defoliation was heavy, with significant feeding on most leaves and the beginning of feeding on fruit. This is very early to find such a heavy population of beet armyworms on cotton in North Carolina. This situation fit all of the general criteria; i.e., conditions were dry and the cotton under stress, the field had already been treated with a pyrethroid, and, based on the very high level of caterpillars, the moths were also there in significant numbers. Except for an adjacent field of lusher B.t. cotton with a far lighter beet armyworm population, I have received no other reports of a moderate or significant establishment of beet armyworms on cotton in North Carolina. South Carolina to date has reported only a few incidents of beet armyworms, while Georgia has been experiencing high levels of beet armyworms in a number of cotton fields. I will keep an eye on this situation. Tracer is the only registered insecticide in North Carolina which provides acceptable control of beet armyworms. The cost of this insecticide is an expensive $13.97 to $17.67 per acre for the recommended 2.2 to 2.9 ounces per acre, respectively. Let's hope that this does not mark the beginning of more widespread problems. A return to above average to excessive rainfall patterns usually relegates beet armyworms to levels that are not economically significant.
Some treatments were underway in the Cove City area for fall armyworms this past week. Conditions are favorable for this pest to increase in the next few weeks, most likely in the southern and southeastern parts of the state. This pest is very difficult to control when the larvae attain any size. In an insecticide evaluation against medium to large-sized fall armyworms in Onslow County a few years ago, control ranged from 36 percent with a high rate of Curacron and Larvin down to 18 percent with the highest labeled rate of Bolstar. None of the newer materials (Tracer, Pirate, Confirm, etc.) provides acceptable control of beet armyworms. Fall armyworms are best controlled when the insecticide is already on the plants at the time of egg mass hatch. Pyrethroids can provide fair to good control of fall armyworms under these circumstances. For escaping fall armyworms, or those which begin to feed on the inner surfaces of the bracts of medium to large bolls, a pyrethroid (assuming some level of bollworms, which is most often the case) plus Curacron, Larvin or Lorsban tank mixed in the range of 0.25 to 0.5 pound of active ingredient per acre can provide a fair level of fall armyworm control. This pest also bears watching.
Cotton aphids also have increased around much of the state's cotton
acreage. Scouts should be able to recognize the cotton aphid
predators, such as lady bird beetles and their larvae, as well as
aphid mummies and the common parasitic fungus. Due to resistance
and the effectiveness of the mummifying wasp parasite and the
fungus, insecticide treatment is normally discouraged. If the
aphid population covers a large portion of the field, with wilting
of the plants due to large colonies of feeding aphids, honeydew is
present on most plants, and little or no evidence of mummies or the
fungus, treatment may be warranted. However, producers may want to
test the insecticide on the aphid population in a small part of the
field first to determine if the aphids are resistant to the
insecticide.
Web page last updated on July 27, 1998 by Stephen J. Toth, Jr..
