Departments of Plant Pathology and Entomology
North Carolina Cooperative Extension Service
North Carolina State University

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North Carolina Pest News
Volume 11, Number 19, August 23, 1996
Stephen J. Toth, Jr. and Thomas A. Melton, editors

The information and recommendations in this newsletter are applicable to North Carolina and may not apply in other areas.

From: Jack S. Bacheler, Extension Entomologist

Insect Pests of Cotton

The present September bollworm flight, although not particularly large and composed, so far, of very few tobacco budworm moths, is producing high egg levels in a number of late-planted, or otherwise lush, cotton fields. Light trap counts as a whole are still declining with some traps in the teens to mid 30's for a two-night trap catch, while a few counts (i.e., a trap in Sampson County) are in the range of 200 moths. Egg counts in the 50 to 100+ range per 100 terminals with 4 to 10 percent small larvae (often still showing up under bloom tags) have been reported in the past few days in some of these late-maturing fields; these are obvious treatment situations. A significant proportion of our cotton acreage was treated this past week for bollworms, especially where the moth pressure on susceptible plants remained high, and the last pyrethroid application was 10 to 15 days prior. A few of our fields in the northern counties of North Carolina were just treated with insecticide for the first time; it looks like this single application will suffice and hold damage to very low levels. Conversely, the very high egg pressure on some of the acreage in southern North Carolina has resulted in 5 insecticide applications.

A significant portion of the state's cotton acreage has cut out and is beyond the potential for budworm or bollworm attack (only medium to small bolls present in terminals). Growers should be reminded to use a higher threshold for bollworms if scouting is confined to upper, smaller bolls.

Soybean loopers were showing up in a few more cotton fields, but so far this year at much lower levels than a year ago. It would appear that soybean loopers will likely be only a minor problem; their defoliation may even be a help in some situations where lush, dense foliage and lack of air flow might contribute toward boll rot.

Beet armyworms are still present a number of cotton fields throughout North Carolina, but their populations seem to be low and on the decline. Our generally wet weather (wetter than last year at this time) and lack of the moth numbers (such as those migrating into Sampson and Harnett Counties in 1995) have been at least partially responsible for these low levels of beet armyworms. A lack of recent insecticide spraying and moderate to high levels of certain beneficial insects has also helped. Occasional rain should also hold beet armyworms at bay in a given field or area. Also remember that all of our presently-labeled insecticides, with possible exception of Dimilin as an early, multiple-application preventive treatment, can be expected to provide poor (but costly) control. And unless our present beet armyworm populations on cotton increase ten-fold or more in the next week or so, we would not meet the criteria (widespread, significant economic loss) for a Section 18 Emergency Exemption for the new generally effective and costly insecticides which have not received federal labels, such as Confirm and Pirate.

Fall armyworms are also present in a number fields throughout North Carolina, but have generally declined during the past week, with fewer larger instar larvae being found on or in bolls than in recent years. As September approaches, producers can disregard the small, mostly second stage, larvae feeding between the inner bract and surface of variously-sized bolls, often low in the plants. These fall armyworms seldom develop into larger boll-damaging larvae. Do not become concerned with the occasional large fall armyworm in blooms and bolls.

European corn borer moth levels are still high enough near significant corn acreage to cause boll damage , particularly in late, ranker cotton fields. However, European corn borer damage does not appear to be bad this year.

This year my damaged boll survey will include a number Bollgard cotton fields so that I can begin to assess the resistance and susceptibility of this B.t. technology to our major cotton pests under grower conditions. This survey will be enlisting the help of county extension agents and consultants in locating a large, representative sample of Bollgard fields.

From: Rick L. Brandenburg, Extension Entomologist

Corn earworms and a few fall armyworms are common in peanuts in North Carolina. Many growers are considering the option of tank mixing an insecticide with their next fungicide application. Remember to scout all fields prior to treating with an insecticide. Many fields have a range of different caterpillar sizes and do not appear threatened with serious defoliation. The threshold for caterpillars normally increases from 4 caterpillars per row foot in August to 8 caterpillars per row foot in early September. Based upon the lush vine growth of most peanuts and the good growing conditions, I believe peanut growers can begin using the 8 caterpillars per row foot threshold a week early (start now).

A number of peanut fields are showing signs of potato leafhopper feeding. The yellowing at the leaf tip is not uncommon, but I often see it occurring a little earlier than this. I believe the mid season buildup of these insects is because we have not experienced the consistently hot temperatures normal for July and August. Many insecticide treatments for corn earworms will also control leafhoppers, but I do not believe leafhopper feeding this late in the season will have any impact on peanut yield.

From: John W. Van Duyn, Extension Entomologist, Vernon G. James Center, Plymouth

Corn earworm populations in soybeans have been common where flowering coincided with the intense but short moth flight. As a result there has been great variation in the caterpillar populations among fields of differing maturity. Additionally, many areas received heavy rainfall at peak egg/small caterpillar density and earworm populations were reduced significantly. So far this season scouting fields has been very beneficial, targeting only those fields with above threshold caterpillar populations. To date, many fields have been treated and corn earworm populations in other fields are now reaching the size where accurate assessment of population can be made.

Although high corn earworm populations have been scattered, the populations of green cloverworms are unusually high over much of the soybean acreage. In my 25 years of work on soybean insects, I have noted perhaps three years where late August/early September cloverworm populations have been damaging. Usually cloverworms are present in soybeans, but are not damaging because they only feed on foliage and suffer high mortality from biological control organisms. However, high populations can cause considerable foliage loss, well above the 15 percent defoliation threshold for reproductive stage soybeans. Assessment of above-threshold populations of cloverworms and other defoliating caterpillars is performed by scouting for foliage loss. Green cloverworms are very easily killed with any of the commonly-used soybean insecticides applied at the lowest labeled rate.

Brown stink bug populations have been high this year in wheat and corn, but I have not seen or received reports of highly-infested soybeans. However, stink bugs are usually September soybean insect pests and growers need to remain alert, especially for seed soybeans. I have seen velvetbean caterpillar moths in soybean fields and Fred May, County Extension Agent, Pamlico County, also reported velvetbean caterpillar moths in his area. Both velvetbean caterpillars and soybean loopers tend to be late season colonizers that seem to be more common in years with tropical storm activity. Perhaps Hurricane Bertha helped to bring these insects to North Carolina this year.

The cotton crop has progressed well in the last week and is declining in susceptibility to insects. However, insect susceptibility is not over yet. Currently moth numbers of both bollworms and European corn borers remain adequately high to cause problems in the later, green and tall cotton. This past week, a lot of fields in Beaufort and Hyde Counties were treated for European corn borers and some cotton fields remain infested above a desirable level. A few cases of insecticide control failures associated with aerial application were brought to my attention. These have involved both bollworms and European corn borers. This is not unusual since caterpillar populations at this time are often deep into the canopy, especially European corn borers, and require optimal canopy penetration to result in adequate success. Low volume (e.g., 1 gallon per acre or less), nozzles arranged to reduce drift, spray droplet evaporation, spray droplet drift away from the target, application obstructions, inadequate swath overlap, and other factors that reduce application effectiveness influence aerial spraying to a great extent. Aerial spraying may be adequate under most situations of low to moderate infestation, especially when caterpillars and eggs are in the upper plant canopy. However, the number of surviving caterpillars (escaped from the insecticide application) may be unacceptably high during events of high colonization and/or when infestation occurs within the canopy, especially when plants are big and canopies closed. This may be especially true if is application is delayed. Application effectiveness (lack of damage) is measured by the number of caterpillars that remain following application, not by how many insects were killed. Under high infestation and/or challenging penetration circumstances, the chances of leaving damaging numbers of caterpillars are high with anything but the best coverage. Sometimes no application technique works as well as desired.

Web page last updated on August 26, 1996 by Stephen J. Toth, Jr..