Clomazone causes excessive cotton injury, but injury is reduced to an acceptable level when applied in combination with disulfoton or phorate. However, these organophosphate insecticides are not perceived to be as effective as aldicarb for early season insect control and cotton seedling vigor. Cotton treated with aldicarb plus clomazone has been reported to yield more than that treated with clomazone and either disulfoton or phorate. The objective of these studies was to determine the effect of these insecticides-herbicide combinations on cotton injury, thrips (Frankliniella spp.), and lint yield.

Experiments were conducted at Jackson, TN during 1992 and 1993 on a silt loam soil of the Lexington series. `Stoneville 453' cotton seed without insecticide treatment were planted in rows spaced 1 m apart and 9.1 m long, four rows per plot. The design was a randomized complete block with a factorial arrangement of clomazone preemergence at 0, 0.56, 0.84 and 1.12 kg ai ha^-1 with a control and four in-furrow insecticide treatments: disulfoton 15G, disulfoton 8E, phorate 20G, and aldicarb 15G. Disulfoton and phorate were applied at 0.84 kg ai ha^-1 and aldicarb was applied at 0.56 kg ai ha^-1. No early season foliar insecticides were applied. Rainfall of 4.5 and 1 cm occurred within 7 days after treatment (DAT) in 1992 and 1993, respectively.

Cotton injury was not evident where disulfoton or phorate were used in combination with any clomazone. Cotton injury increased as clomazone rate increased where no insecticide was used. With aldicarb, cotton injury was about 10% less than in the control in 1992 but 10% more than the control in 1993. Stand loss occurred at all clomazone rates with no insecticide. Stands were reduced somewhat with phorate in combination with clomazone, but not a much as with aldicarb. Disulfoton combinations did not affect stand.

Thrips were fewer with insecticides than in the control, but did not differ consistently among insecticides. Lint yield did not differ among insecticides at 0.56 kg ai ha^-1 clomazone, but at the higher clomazone rates, yields were lower with aldicarb than with either disulfoton or phorate in 1992. No differences were observed between the granular and liquid formulations of disulfoton. Both disulfoton and phorate protected cotton from clomazone injury and provided early season thrips control. While cotton injury and stand loss occurred where aldicarb was used with clomazone, surviving plants at the 0.56 kg ai ha^-1 recovered and lint yield was not reduced partly because there was little thrips damage and plant vigor was good. In 1992, cotton lint yield declined by 23 kg ha^-1 for every 0.1 kg ha^-1 rate increase from 0.56 to 1.1 kg ha^-1 even with disulfoton or phorate, and in 1993 yield declined 13 kg ha^-1 for every 0.1 kg ha^-1 clomazone--even with disulfoton and phorate. Both insect and weed control without injury are important for maximum yield.