Influence of Cultivars and Insecticides on Cotton Tolerance to DPX-T9595

L.M. Kent, C.E. Snipes, and G.D. Wills


 
ABSTRACT

DPX-T9595 is a new postemergence sulfonylurea herbicide candidate for selective control of broadleaf weeds in cotton. Greenhouse studies were conducted in 1988 to determine the tolerance of nine cotton cultivars to DPX-T9595 at the rates of 0.0312, 0.0625, 0.125, 0.25, and 0.5 oz ai/A. Nonionic surfactant at 0.25% v/v was used in all treatments. The cotton cultivars selected were DES 119, Deltapine 20, Stoneville 506, DES 422, Deltapine 50, Stoneville 453, Terra C40, Coker 139, and Stoneville 825. Separate experiments were conducted to determine the influence of five insecticides on the tolerance of DES 422 to DPX-T9595 at 0.125, and 0.25 oz ai/A when tank-mixed. The insecticides and rates selected for this study were Asana® (esfenvalerate) at 0.05 lb ai/A, Cygon® (dimethoate) at 0.2 lb ai/A, Larvin® (thiodicarb) at 0.75 lb ai/A, Lorsban® (chlorpyrifos) at 0.5 lb ai/A, and Orthene® (acephate) at 1.0 lb ai/A. All experiments were conducted twice as a randomized complete block with a factorial arrangement of treatments with 4 replications. Treatments were initiated at the 2- to 3-leaf stage of cotton for all experiments. Phytotoxicity ratings for the cultivar study were made at 7 and 14 days after treatment (DAT). Fresh weights were recorded and converted to percent of the control at 14 DAT. Phytotoxicity ratings were combined across experiments for analysis while the percent fresh weight data were analyzed separately.

Phytotoxicity ratings for the insecticide study were made at 3, 4, 7, and 14 DAT. Fresh weights were recorded and converted to percent of the control at 14 DAT. With the exception of 7 DAT ratings, all phytotoxicity ratings and fresh weight percentages were combined across experiments for analysis.

In the cultivar study based on phytotoxicity at the 7 and 14 DAT, injury ranged from 5% at the 0.0312 oz/A to 22% at the 0.5 oz/A of DPX-T9595. Increasing injury occurred with increasing rates of the herbicide for all cultivars. Based on slope comparisons of phytotoxicity over increasing herbicide rates, all cultivars were equally tolerant. Based on percent fresh weights, DPL 50, Terra C40, and Coker 139 were less tolerant than other cultivars in one of two experiments. Based on fresh weight percentage, these cultivars revealed a slight adverse response to DPX-T9595. However, this response was not consistent across herbicide rates and experiments.

Phytotoxicity ratings with the herbicide-insecticide combinations showed no differences at 3, 4, and 14 DAT when compared to the herbicide alone at rates of 0.125 and 0.25 oz/A. At 7 DAT, DPX-T9595 at 0.125 oz/A tank-mixed with Lorsban and at 0.25 oz/A tank-mixed with Cygon showed greater phytotoxicity than the herbicide alone when compared in one of the twoexperiments. However, phytotoxicity did not exceed 20% and there were no differences in fresh weight after 14 days. Based on these results, there appears to be little adverse effect of DPX-T9595 on cotton with respect to type of cultivar or insecticide.



Reprinted from Proceedings: 1989 Beltwide Cotton Research Conferences pp. 385 - 386
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998