FIELDAND
FORAGE
CROPS
FIELD
The information and recommendations in this newsletter are applicable to
North Carolina and may not apply in other areas.
Cotton producers may be tempted to omit an at-planting insecticide treatment and rely solely on foliar treatments for thrips as mid- May approaches and we get further into better germination, stand emergence and seedling growth conditions. This option is not recommended. As a general rule, producers can probably cut back on the rate of their at-planting insecticide to about 40 percent (e.g., 3 versus 5 pounds of Temik 15G) after mid-May due to the anticipated shorter time period in which seedling must be protected (the time between expanded cotyledon to 6 to 7 true leaf stage) and the typical decline of migrating adult thrips populations as June approaches. However, because late-planted cotton can not afford to be further delayed in its development, thrips protection, though for a shorter time interval, is extremely important. Therefore, at least a 60 percent rate of an at-planting insecticide is recommended for all late-planted cotton.
Cotton plants should be scouted approximately weekly for live thrips and their damage. Examine the terminals of 25 to 50 plants throughout the field. Both crinkled or possum-eared leaves and the presence of immature thrips should be confirmed prior to remedial treatment. Magnification with a 15 to 30x hand lens may be required to find the active, yellowish-colored immature thrips. Emphasis should be directed toward the newer, unfurling leaves; older leaves remain crinkled and thus reveal little, if any, recent information. As an alternative, several seedlings may carefully picked and rapped sharply against either a white or a dark flat surface (an index card or a shallow box will work). A treatment threshold of two immature thrips per plant is suggested.
As a general rule, earlier-planted cotton fields require a more
extended period of protection and may show symptoms of thrips
damage first. Also, Temik at times provides more extended thrips
control than Thimet, Di-Syston, Payload and certainly Gaucho-
treated seed. Finally, hot, dry, windy weather often generates
higher adult thrips populations on cotton (flying from drying
alternate hosts onto cotton). Try to respond to these potential
differences in thrips levels and injury by grouping fields. A
foliar treatment may be required in some situations and not others
on the same farm. Remember as June approaches, treatments with any
foliar insecticide recommended for thrips control can destroy
beneficial insects to the point that the odds of having to treat
for June tobacco budworms may increase dramatically (except on
Bollgard cotton). Good pesticide stewardship and economics dictate
that cotton be treated for thrips only when needed, especially in
the southern half of the state. Automatic foliar treatments for
either thrips or plant bugs should be strongly discouraged.
Blue mold in the United States is still only known to occur in Florida and Texas. The Florida case involved Ridomil-sensitive blue mold. As of May 9, no threatening sources exist.
Bacterial soft rot and Pythium still seem to be causing some problems. Most tobacco growers have had good success with Agrimycin for soft rot control. It does not control any of our other problems. Where growers with Pythium have used Ridomil remedially, root re-growth has usually been good. In some cases, it has been slower than preferred, but it still occurred. We have had more Pythium this year, both in greenhouses that were initially treated and those that were not treated. In greenhouses where Pythium was a problem and where the grower has kept the Ridomil level at a minimum of 1 oz. per 1000 gallons from identification of the disease through transplanting time, I believe the plants can be safely transplanted. Some wilting may occur, but rooting should be normal. Let me know if you see anything otherwise.
Watch for the tomato spotted wilt virus early. Disease symptoms in young transplants are not distinct; scattered plants just die very fast. Georgia is having one of their worst years with this disease, already reporting a statewide average stand loss of 12 percent.
Web page last updated on May 12, 1997 by Stephen J. Toth, Jr..
