Watch for thrips in young cotton crop

“Although late planting of cotton is certainly not recommended in North Carolina, some individual fields or even areas are almost always planted to cotton after mid-May, or even into early June, due primarily to various weather-related factors.”

In North Carolina, thrips in most years ranks as the Number Two pest of cotton, second only to the cotton bollworm, both in terms of control costs and in potential yield loss and maturity delays.

With our northern climate and resulting relatively short production season, thrips control is an important component of profitable cotton production. An early, vigorous cotton crop also helps set the stage for late-season management opportunities such as enhanced control of bollworms and European corn borers, ease of defoliation and earlier harvest.

In cotton with conventional row-spacing (30 to 40 inches), the use of an at-planting insecticide should be considered automatic. This is still true (or perhaps especially true) in a year of low anticipate cotton prices.

Untreated checks in replicated university trials often lose 100 to 300 pounds of lint per acre to thrips damage and maturity delays, compared to the plots with an at-planting insecticide.

In cases of limited at-planting insecticide persistence (for example, sometimes seen with Gaucho-treated seed), high thrips populations, poor insecticide uptake or slow grow off, foliar treatment(s) may be needed.

Foliar treatment(s) should be based on the finding of crinkled (or possum-eared) young leaves and/or deformed or darkened buds along with one to two thrips per plant, if possible.

In Roundup Ready cotton, this application(s) can be very inexpensive if piggy-backed with Roundup (or other glyphosates), and often coincides with a time of cotton plant vulnerability to thrips (one to four true leaves).

The best timing of the foliar treatment often coincides with seedlings reaching about the first true leaf stage. In a typical year, approximately 25 percent of North Carolina's cotton acreage receives a foliar treatment for thrips, although 60 to 70 percent of our cotton was sprayed in 1999 and in 2000.

Listed below are several at-planting and foliar spray options for thrips control in conventional row cotton:

Temik 15G — Temik at the four to five pound product rate generally provides good thrips control and suppression of early season cotton aphids, and is considered a standard in North Carolina.

Although not always significant, Temik often provides earlier grow-off and fruit set, greater persistence, earlier maturity and higher yields than other products.

Due to a lack of safening from Command-caused phytotoxicity, do not use Temik with this herbicide applied PPI or pre-emergence unless a labeled rate of Di-Syston or Thimet is also used.

Di-Syston 15G and 8EC — In most cases, this product provides acceptable thrips control without maturity delays, particularly with later planting dates. Expect somewhat shorter residual activity, however, and the likelihood of higher aphid numbers.

Producers should be careful to avoid planting with Di-Syston under cool, wet conditions, although leaving out the PPI or pre-plant herbicides, as is sometimes done with Roundup Ready and Buctril-tolerant varieties, may lessen maturity delays.

Di-Syston 8EC, sprayed from a single nozzle directly into the open seed furrow, may provide more uniform safening from Command injury than the granular formulation of this product, although this application must be precise.

Thimet 20G — Due to Thimet's generally greater adverse effect on maturity and yields, and less persistence for thrips control than Temik, North Carolina producers are advised to use Thimet with caution. However, Thimet will do an adequate job of thrips control without significant maturity delays and yield reductions if thrips levels are low to moderate, and conditions for Thimet uptake are good.

Planting into warm soils is strongly advised. (Command comments about Di-Syston are also appropriate for Thimet.

Gaucho Seed Treatment — This worker-safe approach to early season thrips control has looked impressive in 1995 to 2000 tests in all parameters except one — persistence. The Gaucho plots usually sustained higher immature thrips levels than all of the above options after three weeks from planting; in some cases the Gaucho plots showed higher thrips levels than the untreated checks.

Gaucho provides good control of cotton aphids.

Although maturity and yields have been very similar to Temik in some tests, Gaucho yields dropped off in moderate to heavy thrips pressure when conditions for late-season plant compensation were poor. Do not depend on more than three weeks' protection from this seed treatment from the time of planting.

Gaucho seed treatment, coupled with an early foliar treatment such as Orthene, has performed will, and is very reasonable when the foliar product is piggy-backed with Roundup (or other glyphosates) or Buctril.

This product would also likely be an acceptable choice for cotton planted after about May 15.

(5.) Adage Seed Treatment — Under North Carolina conditions, the benefits and limitations of Adage seed treatment are almost identical to those of Gaucho — convenience, safety, and good aphid suppression, but are limited to about a three week protection window from thrips from the time of planting.

(6.) Foliar treatments — Automatic applications for thrips (instead of an at-planting insecticide) are generally to be avoided. Although inexpensive when applied in a band during a cultivation or over-top herbicide trip, these products provide limited residual control and, can contribute to secondary outbreaks of cotton aphids and budworms.

However, well-timed, need-based foliar treatment(s) can have a significant positive impact on early plant growth, maturity and yields.

Do not overlook the possibility of a very early scouting-based treatment at the expanded cotyledon stage when the first true leaf is just visible.

When the cotton plants have an average of approximately five to six true leaves, thrips control should no longer be necessary if adequate moisture exists.

Although late planting of cotton is certainly not recommended in North Carolina, some individual fields or even areas are almost always planted to cotton after mid-May, or even into early June, due primarily to various weather-related factors.

If cotton is planted after May 15, or thereabouts, 60 percent of the at-planting insecticide rate (for example three pounds of Temik 15G per acre) will probably offer enough thrips protection, given the expected rapid grow-off conditions.

The other options listed above, such as Gaucho and Adage seed treatments, and Di-Syston and Thimet, may also provide adequate thrips protection without the need for supplemental foliar treatment.

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