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Field and Forage Crops |
The predominant cotton insect pest, both for now and, unfortunately, probably through our first killing frost, continues to be the beet armyworm. Beet armyworms are primarily defoliating cut out cotton plants that are mostly past the point of damage, and are generally avoiding the later-maturing lush cotton plants, at least for now. Although even low to moderate levels of beet armyworm feeding on leaves may appear alarming, many cotton fields with high numbers of beet armyworms may not be in need of treatment with insecticides. This insect species is a defoliator by choice, a square and bloom feeder secondarily, and a boll feeder as a last resort, usually after significant defoliation has taken place. Insecticide treatment at this time of year should be confined to situations where extensive defoliation of most plants threatens the individual leaves at the base of harvestable bolls that are still filling out, or if defoliation is so extensive that an average one or more beet armyworms on fruit is resulting in damage to medium and large bolls, or their stems (peduncles).
Fall armyworms have been occurring at treatable levels in a few cotton fields in the past two weeks. These pests should be managed more like bollworms, with treatment triggered by finding 3 to about 5 small fall armyworms in blooms or on bolls, and thresholds adjusted upwards according to the proportion of large speckled versus smaller bolls and blooms. Although fall armyworms are controlled to a limited degree with pyrethroid insecticides, Larvin, Lannate, Intrepid, Steward or Tracer may be needed to control fall armyworms which are becoming established. Unlike beet armyworms, medium to large fall armyworms are very difficult to control with insecticides. On the positive side, fall armyworms appear to have great difficulty becoming established on bolls after about September 1 in North Carolina, typically confining their feeding to the inner surface of boll bracts. Up to this point, very few cotton fields have been treated specifically for fall armyworms.
Bollworm moth levels are still high enough in many areas of the state to congregate in late-maturing cotton fields which have not yet cut out. Even in these fields, further treatment is often hard to justify due to the number of bollworm-safe larger bolls.
This week I received a note from Vance County about sick horses and blister beetles in the pasture. Blister beetles are rarely considered pests, but sometimes concern alfalfa growers. Larvae are normally predaceous on grasshopper eggs and serve a beneficial function. Although adults may consume foliage, the greater concern seems to be for horses which coincidentally ingest the beetles while feeding on alfalfa hay. Blister beetles contain body fluids which can severely irritate the mouths and stomachs of horses. Even a few beetles ingested can cause colic or death to a horse. This beetle is gregarious and growers can watch for concentrations of these beetles when cutting hay. Avoid harvesting areas of high concentrations of beetles, particularly if the forage is to be fed to horses. Spot treatment in the field with carbaryl may be used if needed. Blister beetles are a more common problem from alfalfa hay brought in from the midwestern states than from hay produced in North Carolina. Blister beetles tend to be more problematic in dry weather.
Two words describe the insect situation in peanuts, which are worms and mites. It has been a very difficult growing season in many ways and now the insects and mites are making it even more challenging. We are finding a lot of corn earworms, fall armyworms and beet armyworms. The moth flights indicate the problem is not over. Fall armyworms are more difficult to control than corn earworms, and beet armyworms are the toughest of all to manage. Lannate can control the smallest beet armyworms, but only Steward will control larger beet armyworms. The beet armyworm does not reach as large a size as a corn earworm, so a big beet armyworm will be smaller than a large corn earworm. In some years we have had problems with fall armyworms chewing on the pods once they are dug. Be alert to this situation and if small to medium fall armyworms are present as peanuts near harvest, control may need to be considered. Keep in mind any preharvest restrictions. If large worms are present near harvest, treatment may not be necessary as the worms will pupate before harvest.
Lesser cornstalk borers are also present in many areas where conditions are very dry. Only Lorsban is labeled for control of lesser cornstalk borers and the granules require a rain to activate the product and begin to control the worms.
Mites are also flaring up in many areas. Comite and Danitol are the two options, with Danitol effective against both mites and worms. Danitol will control fall armyworms and corn earworms.
Currently, an important question for many growers is whether or not there will be an economic return from treatments. That decision must be made on a field-by-field basis. If the grower has a reasonable crop and it has potential, then the question may be easier to answer.
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 August 26, 2002 by Stephen J. Toth, Jr.