At-Planting Insecticide Options Explored

Jack S. Bacheler

North Carolina Extension Entomologist

In North Carolina, with its northern climate and resulting short production season, thrips control, along with other maturity-enhancing practices, has become an important component of profitable cotton production. An early,vigorous cotton crop helps set the stage for late-season management opportunities such as enhanced control of bollworms and European corn borers and greater ease of defoliation and early harvest. Lack of at-planting insecticide persistence, high thrips populations, poor insecticide uptake or slow growoff can translate into foliar treatment(s) for thrips which in turn can result in

the need to spray for secondary cotton aphids and early tobacco budworms (except in B.t.Bollgard cotton), cotton aphids and, sometimes, spider mites. In 1997, under heavy thrips pressure and poor early growing conditions, North Carolina producers treated over one half of the state s cotton acreage with a foliar application for thrips; some of this acreage was treated 2-3 times. On the average, approximately 25% of this state s cotton acreage receives a foliar application for thrips. Cotton aphid, plant bug and spider mite levels were the highest across the board than experienced in the past 15 or so years.

Under these circumstances, Temik 15G provided the most consistant thrips control and generally held cotton aphids to lower levels than the at-planting alternatives Thimet 20G, DiSyston 15G and 8E, Gaucho seed treatment, and various other seed treatment and in-furrow sprays. Alternatives to Temik may be appropriate in certain situations. The basic options available to North Carolina producers and a few comments are listed below:

1. Temik 15G - Temik at the four to five pound product rate generally provides good thrips control and suppression of early season cotton aphids. Although not always significant, Temik often provides earlier grow-off and fruit set, greater persistence, earlier maturity and higher yields than other products. If cotton is planted after May 15 (not recommended), 3 pounds of product should suffice because of the shorter protection window needed. Due to a lack of safening from Command-caused phytotoxicity, do not use Temik with this herbicide applied PPI or pre-emergence unless 0.75 lb active/acre of Di-Syston or Thimet is also used.

2. Di-Syston 15G and 8EC - In most cases, this product provides good thrips control and maturity rates similar to Temik, particularly with later planting dates, but typically expresses shorter residual activity. Producers should be careful to avoid planting with Di-Syston under cool, wet conditions. 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.

3. Thimet 20G - Due to Thimet's generally greater adverse effect on maturity delays 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 under most circumstances. Planting into warm soils is strongly advised. (Command comments about Di-Syston also appropriate for Thimet.)

4. Payload 15G - All of the Payload being sold in 1997 has been reprocessed . The harder Payload granules should be less prone to the humidity and flow problems sometimes associated with the previous commercial product. This reprocessed version and a number of new formulations will be evaluated this spring, so the ease of use of 1997 Payload 15G won t be known under a wide range of planting circumstances in time for this season. The company tells us that the bridging problems have largely been solved. Along with Gaucho seed treatment, Payload is the safest product on the market. The high human and wildlife safety features associated with this non-restricted product render its use under Worker Protection Safety Standards more convenient than its competitors. Despite being an organophosphate insecticide, acephate (Orthene 75S, Payload 15G) will not provide sufficient protection (safening) from Command injury.

5. Gaucho Seed Treatment - This highly-promoted, safe approach to early season thrips control looked impressive in all parameters evaluated in 1995 and in 1996 except one- persistence. Depending upon the test, the Gaucho treatment sustained higher immature thrips levels than all of the above materials, in some cases supporting thrips populations than the untreated check. Oddly, maturity and yields have been very similar to Temik in tests, although Gauch yields dropped off somewhat in 1997 under the high thrips pressure and poor plant compensation conditions experienced at test sites. Producers are again urged to try this product on limited acreage in 1998. This product would likely be a good choice for cotton planted after about May 15. In a 1997 ultra narrow row cotton test, Gaucho seed treatment, along with an Orthene foliar spray tied for the highest economic return with Temik.

6. Foliar Treatments - Foliar applications for thrips, particularly automatic treatments following the use or instead of an at-planting insecticide, are generally to be avoided whenever possible. Although inexpensive when applied in a band during a cultivation trip, these products provide limited residual control and, can contribute to secondary outbreaks of cotton aphids abd budworms. However, well-timed, need-based foliar treatment(s) can have a significant positive impact on early plant growth, maturity and yields.

If foliar treatments are used, they should be made with discretion and based upon scouting and identifying newly-emerged possum-eared leaves and two or more active immature thrips per plant typically found upon the undersides (mostly) and within the folds of young leaves; a hand lens may be necessary to see the very small immature thrips and a pair of tweezers helpful in teasing apart the small bud areas to reveal the immatures. Do not overlook the possibility of a very early treatment at the expanded cotyleden stage when the first true leaf is just visable.

When the cotton plants have an average of approximately 5-8 true leaves, thrips control should no longer be necessary in most situations if adequate moisture exists.