Thrips Control in Ultra Narrow Row Cotton in North Carolina

Jack S. Bacheler, Extension Entomologist
North Carolina State University
(CCN - 00 - 3c  March 2000)

Thrips control gets both interesting and potentially very expensive in ultra narrow row (UNR) cotton. With the focus on establishing and protecting first position fruit in UNR cotton, thrips control also takes on a greater urgency. With approximately a 5-fold increase in the number of row feet per acre (7.5 inches vs. 38), rates of at-planting materials must increase proportionally to provide the same amount of insecticide per foot of row. Thus, a 4 lb. rate of Temik 15G costs just about $12 per acre on conventional cotton; yet this same amount per row foot would cost almost $60 per acre on 7.5-inch UNR cotton! With seed treatments such as Gaucho, the expense increases approximately 3-fold, in proportion to the increased plant population in UNR compared with conventional cotton. Broadcast foliar treatments for thrips are the same in conventional row spacing and in UNR cotton.

To look at the economic returns of several thrips control options in UNR cotton, replicated tests were conducted in 1997 and 1998 to evaluate the at-planting insecticide Temik, Gaucho seed treatment, with an without a foliar spray, an Orthene 75S foliar spray treatment and doing nothing. The Temik 15G rate was 15 lb. per acre, which provided the same amount of material per row foot as the 3 lb. rate of Temik in conventional, 38-inch row cotton. The results are summarized in Table 1.

Table 1. Thrips control in UNR (7.5-inch) cotton;
Rocky Mount, NC 1997-1998

* Thrips sample taken 4 weeks after planting.

** Costs and values: cotton - $0.70/lb.; Temik - $45.00/A; Gaucho - $19.71/A; Orthene - $2.19/A (when sprayed with Roundup); Orthene plus appl. cost - $5.19.

All options, except for the Gaucho seed treatment alone and the untreated check, provided adequate thrips control, averaging less than two thrips per plant. One can readily see why Gaucho seed treatment must often be supplemented with a foliar insecticide spray.

Interestingly, the overall returns for the Gaucho seed treatment plus an Orthene foliar spray, two Orthene foliar sprays, and the Temik treatments were relatively close, despite widely varying control costs. However, if the price of cotton were set at $0.55/lb, the two Orthene spray treatment and the Gaucho plus one Orthene spray option would have shown returns of approximately $16 and $13 per acre more than the Temik treatment (approx. $419 and $416/acre returns vs. $403 for Temik), indicating that these first two options may better choices with low cotton prices, at least with this high rate of Temik. However, given the greater potential for beneficial insect disruption and subsequent outbreaks of secondary pests with the first two foliar options, Temik might still have been a viable option, at least in higher yield situations, with higher traditional thrips pressure, or at higher cotton prices.

In two1999 tests in Wilson County, NC Temik at the lower 8.0 pound rate (1.2 lb. active/acre) was cost competitive, despite the poor uptake and resulting high thrips levels (Table 2). In these tests, all three Temik rates showed the highest yields, although the 8.0 lb. product rate showed the greatest net returns. Not shown in the Table 2, the Temik treatments also showed greater plant heights and stands at seven weeks after planting.

Table 2. Economic returns of selected thrips control options in ultra narrow cotton near Lucama, NC, 1999 (2 tests).

Means sharing the same letter are not significantly different (p = 0.05; LSD)

* Average of three thrips assessments @ 3, 4 and 5 weeks after planting.

** Value is the yield at various lint prices minus insecticide cost.

In summary, in comparing the value of various thrips protection options- 1) an at-planting insecticide treatment, such as Temik, 2) Gaucho seed treatment plus a foliar treatment(s), or 3) foliar sprays- no single option appeared to have a clear advantage. However, even with expected low cotton prices, whatever the option selected, good thrips management must be taken seriously in UNR cotton.