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Field and Forage Crops |
Over the long haul, the value of using an at-planting insecticide to reduce thrips damage will outweigh the cost of the insecticide. Gaucho or Cruiser seed treatment will probably require additional spray protection for thrips, but these products can be cost effective, especially with an early application of Roundup or Ignite over Roundup Ready or Liberty Link cotton, respectively. At the first true leaf stage, Temik 15G at the 5 pound product rate remains North Carolina's standard for thrips control, and will less likely require foliar protection for thrips than the seed treatments. Using either Temik or the seed treatments plus a foliar spray should provide cotton aphid protection for four to five weeks or more under conditions of adequate moisture.
Most of the foliar sprays for thrips such as Orthene, while often needed during the past three or the past four years' "thripy" springs, will sometimes increase cotton aphid numbers. We do not recommend the use of foliar sprays alone in conventional row cotton. Ultra narrow row cotton, with its high in row seed protectant costs, is an exception, although Temik at low rates and a seed treatment plus a foliar application were cost-competitive to the "foliar spray alone" approach in ultra narrow row cotton in replicated tests conducted here in 1997 and in 1998.
With our recent history of early, high thrips levels, do not overlook the possibility of thrips establishment and damage as early as the expanded cotyledon to the first true leaf stage. In 2002, we found moderate to high thrips levels on cotton seedlings just coming out of the ground. So these insects can get started early.
Remember that thrips must be taken seriously in the Carolinas and Virginia, and measures to protect cotyledon to 4 to 5 true leaf cotton seedlings from significant thrips damage are usually justified.
With various forms of conservation tillage (such as stale seedbeds, no-till or strip till), weed residue (especially if burned down less than two and a half or three weeks of planting) can support damaging levels of cutworms, which can then move onto the remaining green foliage (i.e., cotton seedlings). Scouting for cutworms and insecticide treatment based on a stand loss of about 10 percent along with live cutworms is recommended where possible, although the thoroughness of the scout, the size of the cutworms, the distribution of the damage and the density of the plant stand itself should be taken into consideration. Cutworm scouting is difficult, as these caterpillars invariably "hide out" below the soil surface under clumps or within cracks during the day.
A history of cutworm damage in a conservation tillage cotton field, if known, may argue for insecticide treatment. This can be done cheaply with a broadcast or banded pyrethroid insecticide application prior to, during, or just after planting. In general, however, significant cutworm reductions to stands are much more the exception than the rule, even in reduced tillage cotton.
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Last modified on May 3, 2004 by Stephen J. Toth, Jr.
