Trifloxysulfuron Plus Pyrithiobac Mixtures for Broadleaf Weed Control in Cotton (Gossypium hirsutum)1

Studies were conducted in 1999, 2000, and 2001 to evaluate broadleaf weed control in cotton from POST applications of trifloxysulfuron plus pyrithiobac. Trifloxysulfuron was applied at 2.5, 5, and 7.5 g ai/ha, and pyrithiobac was applied at 0, 17, and 35 g ai/ha in a factorial treatment arrangement. Cotton injury was affected by rates of both herbicides at 7 and 14 d after treatment (DAT) with injury ranging from 19 to 26%. Broadleaf weed control at 28 DAT from mixtures of the herbicides was generally commercially acceptable. Combinations of 17 or 35 g/ha pyrithiobac plus trifloxysulfuron controlled common ragweed, velvetleaf, common lambsquarters, annual morningglory species (ivyleaf morningglory, pitted morningglory, and tall morningglory), common cocklebur, spurred anoda, and jimsonweed at least 73% at 28 DAT. Trifloxysulfuron applied alone failed to control velvetleaf, spurred anoda, and jimsonweed. Cotton yield reflected weed control and yields increased with pyrithiobac rates. It is concluded that the spectra of the weeds controlled by trifloxysulfuron and pyrithiobac were highly complementary in these studies. Nomenclature: Trifloxysulfuron; pyrithiobac; annual morningglory species, Ipomoea spp.; common cocklebur, Xanthium strumarium L. #3 XANST; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L # AMBEL; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; jimsonweed, Datura stramonium L. # DATST; pitted morningglory, Ipomoea lacunosa L. # IPOLA; spurred anoda, Anoda cristata (L.) Schlecht. # ANVCR; tall morningglory, Ipomoea purpurea (L.) Roth # PHBPU; velvetleaf, Abutilon theophrasti Medicus # ABUTH; cotton, Gossypium hirsutum L. Additional index words: Acetolactate synthase (ALS), herbicide mixtures. Abbreviations: ALS, acetolactate synthase enzyme (EC 4.1.3.18); POSD, postdirected.