Field experiments were conducted in 2003 and 2004 to evaluate the effects of reduced rates of glufosinate on development and yield of three nonglufosinate-resistant cotton varieties. The varieties evaluated were selected on their relative maturity with PayMaster (PM) 1218, early maturity; FiberMax (FM) 960, medium maturity; and Delta and Pine Land (DP) 555, late maturity. Rates of 47, 23, and 4.7 g ai/ha were applied, representing 10, 5, and 1% of the typical use rate per application of 467 g ai/ha, respectively. As might be expected, when averaged over varieties, the 10% rate showed more injury than the 5%, and the 5% rate caused more visual injury than the 1% rate. Pooled over timing and rate, PM1218 showed more injury (18%) than FM960 (7%), which showed more injury than DP555 (1%) 7 days after application (DAA) at the 10% rate. However, although PM1218 showed the most visual injury, this did not translate into delay in maturity or loss of lint yield. DP555 showed 70 kg ai/ha and 50 kg ai/ha lint yield loss when glufosinate was applied at the 10% rate on the fifth and eighth node stage, respectively. DP555 was delayed in maturity when glufosinate was applied at the 10% rate on the eighth node stage. FM960 showed 30 kg/ha lint yield loss when glufosinate was applied at the 10 and 5% rates at the fifth node stage. Maturity of FM960 was delayed with the 10 and 5% rates applied at the fifth node stage.

Nomenclature: Glufosinate, cotton, Gossypium hirsutum L., ‘Delta & Pine Land’ (DP555), ‘FiberMax’ (FM960), ‘PayMaster’ (PM1218)