ABSTRACT

The effectiveness of paraquat (PQ) plus sodium chlorate (NaChl) following a standard defoliant application was evaluated in experiments conducted at the Delta Branch Experiment Station in Stoneville, MS, and at the Coastal Plain Experiment Station, Tifton, GA. Standard varieties (DES 119, Stoneville and DPL 90, Tifton) and production practices were utilized at both locations to ensure normal crop growth and optimum defoliation response. Experimental design at both locations was a randomized complete block with 4 replications. Treatments were thidiazuron at 0.1 lb ai/A or tribufos at 1.125 lb ai/A, each followed in 5 to 7 days by PQ, PQ plus NaChl at 3.0 lb ai/A or PQ + NaChl at 6.0 lb ai/A. PQ was applied at 0.07 lb ai/A with non-ionic surfactant included at 0.25% v/v. Thidiazuron and tribufos treatments were initiated at approximately 50% bell opening. Percent defoliation was visually estimated at 7 and 14 days after the last treatment (DAT) on a scale of 0 to 100 where 0 equal no defoliation and 100 equals complete defoliation.

At 7 DAT in Stoneville, tribufos without any sequential treatment resulted in 79, 52, and 65% defoliation in 1989, 1990 and 1991, respectively. Defoliation with tributes was 32 and 72% in 1990 and 1991, respectively, at Tifton. Defoliation with tributes at 7 DAT was not improved by any sequential treatment in 1989 at Stoneville and 1991 at Tifton. However, results from both locations in 1990 indicated improved defoliation with PQ + NaChl at 3.0 lb ai/A following tribufos. In 1991 at Tifton, defoliation at 14 DAT with tributes followed by PQ plus NaChl at 6.0 lb/A was 84% compared to 65% without sequential treatment.

At Stoneville, thidiazuron at 0.1 lb ai/A provided 55, 58 and 82% defoliation at 7 DAT in 1989, 1990 and 1991, respectively. Defoliation with thidiazuron was 36 and 51% in 1990 and 1991, respectively, at Tifton. Sequential treatment did not improve defoliation at 7 DAT with thidiazuron in 1991 at either location- PQ plus NaChl at 3.0 lb ai/A following thidiazuron significantly improved defoliation at 7 DAT from 55 to 70% in 1989 and from 58 to 76% in 1990 in Stoneville and from 36 to 77% in 1990 at Tifton. PQ + NaChl at 6.0 lb ai/A improved defoliation with thidiazuron from 58 to 91% at Stoneville in 1990. Evaluations for thidiazuron at 14 DAT were @ar to 7 DAT evaluations except for Tifton in 1991 where PQ + NaChl at 6.0 lb ai/A significantly unproved defoliation from 63 to 81%. While PQ without NaChl improved defoliation following application of tribufos or thidiazuron in some cases, defoliation was improved more and with greater consistency when PQ was tank-mixed with NAChl.