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The information and recommendations in this newsletter are applicable to
North Carolina and may not apply in other areas.
The large bollworm moth flight has mercifully declined rather sharply over much of North Carolina this past week. Light trap counts were down drastically from a week ago in Scotland and Robeson counties, up in Northampton, Halifax and Chowan counties. For example, the light traps which averaged 484 moths (for 2 nights) on July 31 in Craven, Jones and Onslow counties had dropped to an average of 23 moths on August 7. With the Pee Dee (Florence) area of South Carolina showing light numbers of bollworm moths, we expect to have lower levels of bollworm eggs and small larvae for a while over much of the state. Also blooming, open-canopied soybean fields can siphon off significant numbers of bollworm moths. However, with the tailing off of the major moth flight, the remaining bollworm moths often tend to concentrate in the lusher and/or later-planted cotton fields which may be still in need of protection. Additionally, much of our very early and/or drought-stressed cotton which has already cut out will experience excessive regrowth. This regrowth is attractive to egg-laying bollworm moths. Treatment decisions will need to be made on whether bollworms developing on regrowth can gain enough size to damage lower, older bolls before these bolls are impervious to bollworm attack. Toward the end of most bollworm moth flights, the number of hatching eggs trends downward, both paralleling the lower moth levels and less egg viability (successful hatching). The emphasis now turns more to bollworm establishment on young bolls. If bloom tags and small bolls are being examined almost exclusively on mature cotton, the thresholds may need to be elevated 2 or 3- fold to account for the unsampled (and disproportionally undamaged) large bolls. The next bollworm moth flight should begin this coming weekend in the southern part of the state. It's size and potential impact on late cotton are unknown at this time.
Less insecticide treatment for bollworms in the coming weeks tends to open the door for other potential cotton pests such as fall armyworms, European corn borers and stink bugs. In B.t. cotton , the same is true except that the B.t. toxin will eliminate European corn borers. Fall armyworms may become a headache during the next three weeks, as a few more reports of mostly low levels of primarily small larvae, at least up to this point, have arrived. Fall armyworms can still become established throughout August, and they can invade dry, as well as lush, fields. Identification of fall armyworms as early stage larvae is important, as very poor control of medium to large fall armyworms can be expected with any available insecticides, both new and old. In a 1993 test against medium and large fall armyworms, Curacron, Lorsban, Larvin, Lannate and Bolstar at the highest-labeled rates provided reductions of fall armyworms of only 36.2, 30.0, 30.0, 20.0 and 16.8 percent, respectively. The above insecticides and Tracer will provide fair control of fall armyworms if larvae are small. A threshold of 3 to 4 percent small fall armyworms (on squares, in blooms or on inner bract surfaces of medium and large bolls) would be appropriate. A pyrethroid spray for bollworms within the past few days will also help limit the establishment of young armyworms hatching from egg masses. Be sure you are able to distinguish fall armyworms from bollworms. Young fall armyworms often crawl faster than bollworms, they have a darker head capsule with the central area lighter, the young instars have a black dot on each side just behind their last pair of front legs, bract feeding is common, and their brownish- grey coloration is uniform without the variable color one sees on bollworms.
Both aphid mummies and the parasitic fungus have become more widespread this past week, although aphid levels are very high in many areas of the state. In areas where either of these beneficial organisms are present, treatment with insecticide is not advised. A recent aphicide screening test conducted by Drs. Bradley and Van Duyn, Department of Entomology, North Carolina State University, the organphosphate insecticides and the pyrethroid Capture showed very poor aphid suppression, indicating aphid resistance to these chemicals in the present population. Based on an admittedly limited number of reports, aphid resistance to our standby materials like Bidrin and Cygon seems to be high. In the above test, Provado provided fair to good control of aphids, although the cost for the chemical is about $14.00 per acre for the standard 3.75 ounce rate. And a second application may be required. Aphid control with Provado in a similar test in Bertie County last year did not control aphids on the undersurfaces of upper leaves, but was the best labeled material in another test in Northampton County. Although the high levels of terminal aphid clusters, large aphid levels on the undersurfaces of the upper leaves and sticky foliage are troubling, allowing natural control to work is most often the best approach in managing these high aphid populations. If the above symptoms are present with no signs of mummies or the fungus, treatment may be indicated. If Provado is used, plan to use an organosilicone-based spray adjuvant, adequate water for thorough coverage, and high pressure. If this year is true to form, aphid mummies and the fungus should provide increasing control of aphids in the coming weeks.
It appears the caterpillar populations in peanuts will be higher this year than we have observed in recent seasons. The populations also appear to be a mixture of species, but the majority still appear to be corn earworms. However, it is important to check before treating because the fall armyworm is a little harder to control and may affect your choice of insecticide. Remember that the threshold for caterpillars is 4 per row foot. In most years this is exceeded in only a portion of the fields.
Spider mites are also occurring in a few areas where rain has been limited in the past few weeks. Most of these infestations are still concentrated around the field edges and timely pesticide treatments can prevent further spread. Remember too that a secondary benefit from using the leafspot advisory is a reduced incidence of spider mites in fields under the advisory compared to fields managed for leafspot using a calendar approach to spraying. If you have been not received significant rain in recent weeks, treated for rootworms or caterpillars, or treated for leafspot on a two-week spray schedule, your fields are at greater risk from spider mite attack.
Potato leafhoppers are still present in some fields but do not appear to be as abundant as they were a few weeks ago. Insecticide treatments for caterpillars will also control leafhoppers. Rootworm treatments will also control leafhoppers, but it is too late to receive any benefit for rootworm control from an application of a granular formulation of a rootworm insecticide to peanuts. Danitol will control both spider mites and caterpillars, but do not assume a treatment for caterpillars now will prevent spider mites later. If you have a current infestation of both caterpillars and spider mites, then Danitol may be your best choice due to its activity against both pests.
Sclerotinia blight of peanuts has been seen in several areas throughout the state. Temperatures have been optimal for disease development. Most areas are too dry for significant disease increase. The weather-based advisory has called for sprays in two peanut-growing counties. It is anticipated that substantial rain will cause rapid disease increase in fields with a history of Sclerotinia blight problems.
Growers should be scouting fields as often as possible. Pesticide
sprays should be applied when disease is found or when weather
conditions are favorable for disease development. Daily calls to
local county Extension office to receive weather-based disease
advisories is recommended.
Web page last updated on August 10, 1998 by Stephen J. Toth, Jr..
