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

FIELD
AND
FORAGE
CROPS

North Carolina Pest News
Volume 11, Number 4, May 10, 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

Thrips on Cotton

Present Outlook:Our cool, moist conditions have be replaced with warm to hot days, with little moisture in a number of areas. In general, we can count on increased adult thrips populations flying out of drying weed and small grain hosts onto green hosts such as cotton if these conditions continue. With any of the at-planting insecticides, we can count on at least three weeks of adequate to good thrips control if moisture is adequate. Under favorable conditions (low to moderate thrips populations, good soil moisture and warm weather), growers can expect up to four weeks of protection from the granular materials. Under most circumstances, expect somewhat longer residual control of thrips with Temik. However, for cotton planted under dry conditions where the moisture is just enough for stand establishment, the uptake of any of the at-planting materials may not provide adequate thrips control. If thrips symptoms are noted under these conditions and rain is expected, wait 2 to 4 days until after the rain shower and reassess the plants. The possum-eared leaves present prior to the rain will not be a reliable indicator of possible at-planting insecticide reactivation. Instead, focus attention on the finding of the tiny, yellow-colored immature thrips and the very small unfurling leaves in the plant terminals.

Late-planted cotton: In cotton planted after May 15 (not recommended, but sometimes unavoidable), the lower rates of 0.5 pounds of active ingredient per acre of Temik or 0.75 pounds of active ingredient per acre of Thimet, Di-Syston, or Payload should provide good thrips control with adequate moisture. Although the time of plant vulnerability to thrips damage will, in most cases, be significantly shortened at these later planting dates, do not eliminate these materials. Thrips-related stunting at this late date can not be tolerated by cotton already off to a late start.

Scouting for Thrips: The most efficient way to scout for thrips is to use plant symptoms as the initial screening for more detailed assessments of immature thrips. If moisture is adequate and thrips symptoms are not present (after an examination of plant terminals from several field stops), the plants should be safe for a time. If the newer plant terminals have possum-eared or gnarled leaves, or in extreme cases, stunted, blackened plant terminals, a more systemic scouting for immature thrips is in order. Plants showing damage (or suspected damage) should be checked approximately weekly for live thrips. The 25 to 50 terminal sample should be taken from several locations in the field.

The presence of immature thrips should be confirmed prior to remedial treatment. Magnification via a 15 to 30x hand lens may be required to find the active, yellow-colored immature thrips. Most adult thrips species occurring on cotton can be seen without magnification, and may be tan, black, yellowish or striped and always have tiny wings. A hand lens will be needed to see the wings of adult thrips. Emphasis should be directed toward the newer unfurling leaves; older leaves remain crinkled and thus reveal little, if any, recent information. Alternatively, several seedlings may carefully picked and struck sharply against a white or a dark flat surface (an index card or a shallow box will work). A treatment threshold of 2 immature thrips per plant is suggested. If the plants are significantly stunted an average of one immature thrips per plant may justify. Often under severe stunting, thrips numbers may average 10 to 20 or more per plant.

Treating for thrips: If a foliar treatment for thrips is needed, any of the recommended materials will do a good job; thrips are not difficult to control. Thrips levels will require reassessment in 5 to 7 days if the cotton is still in a susceptible growth stage. When cotton has reached the 5 to 7 true leaf stage with adequate moisture, thrips will no longer cause economic damage even though they will be easy to find. Remember that as June approaches, treatments with any of the foliar insecticides recommended for thrips can destroy beneficial insects which dramatically increases the odds of having to treat for June tobacco budworms. See pages 140-142 in Cotton Information 1996 for more information on thrips management.

From: Tom Melton and Paul Shoemaker, Extension Plant Pathologists

Blue Mold on Tobacco in Florida

We have received the first report of blue mold for the season in cultivated tobaccos. This is all we have at the moment:

Florida Extension Plant Pathology received a sample of tobacco with blue mold on May 8. The grower observed the blue mold on May 6, 1996. So far, the lesions are not sporulating, but with irrigation they probably will sporulate. It has been hot and dry. Associated with the fresh lesions was the presence of a very few old sporulating lesions that likely began during the end of our heavy rains at the end of March. Our dry weather probably checked the spread at that time and therefore the disease went unnoticed. About 8 to 10 days ago, we received 4 inches of rain at these locations. The rain was associated with a south to southeastern moving weather front. On another farm where no irrigation was used, one old lesion was present as in the field mentioned above; no new lesions were present at this site where no irrigation was used. A third field also has blue mold. The three known fields are within Columbia and Union Counties.

Web page last updated on 13 May 1996 by Stephen J. Toth, Jr..