Cotton (Gossypium hirsutumL. ‘Stoneville 213’) was grown with densities of sicklepod (Cassia obtusifoliaL.) or redroot pigweed (Amaranthus retroflexusL.) ranging from 0 to 32 weeds/15 m of row. Regression of seed cotton yields on weed density revealed a linear decrease in yield with increasing weed densities. In the 3 yr these studies were conducted, losses in hand harvested yields of seed cotton ranged from 34 to 43 kg/ha for each sickledpod plant/15 m of row and 21 to 38 kg/ha for each redroot pigweed plant per 15 m of row. Under comparable weed densities, yields of seed cotton differed only slightly when hand harvested or mechanically harvested. Mechanical harvesting efficiencies of cotton were reduced only at higher densities of weeds. The percentage of trash in cotton generally increased with increasing density of weeds. Neither sicklepod nor redroot pigweed affected cotton grade or micronaire.
Tall morningglory [Ipomoea purpurea(L.) Roth.], pitted morningglory(I. lacunosaL.), ivyleaf morningglory [I. hederacea(L.) Jacq.] and entireleaf morningglory(I. hederaceavar.integruisculaGray) were compared for their competitive ability with cotton(Gossypium hirsutumL.) at weed densities of 4, 8, 16 and 32 weeds/15 m of row. Tall morningglory was the most competitive with yield reductions of as much as 88% at 32 weeds/15 m. The higher populations of tall morningglory also significantly reduced cotton populations, mechanical harvesting efficiency and lint percentage below that in the controls. Pitted morningglory densities twice that of tall morningglory were required to produce cotton responses similar to those induced by tall morningglory. Ivyleaf morningglory and entireleaf morningglory were almost identical in their competitive potentials and were less competitive than the other species evaluated. Their competitive ability was greatly reduced by disease. Competition from morningglories did not consistently affect cotton fiber micronaire, fiber length or strength.
Seed cotton (Gossypium hirsutumL.) yields were not reduced when competing with prickly sida (Sida spinosaL.) for 7 weeks or less after cotton emergence and maintained weed-free for the remainder of the season. Cotton yields were not affected when pure prickly sida stands were controlled for 5 to 6 weeks after cotton emergence and then allowed to grow uncontrolled for the remainder of the season. In the more severe weed competition treatments, cotton plant height and main stem diameter were reduced; however, yield of seed cotton was the most sensitive indicator of prickly sida competition. Maturity of cotton, as measured by percent of total yield obtained at first picking, indicated a delay in maturity in 1 of 3 yr in treatments where competing prickly sida was present for 8 weeks or more. In density studies, where prickly sida emerged with cotton and was allowed to compete for the full growing season, 45 prickly sida plants/15 m of row caused reductions in yield of seed cotton in two of five experiments. In another series of three experiments as few as 32 prickly sida plants/15 m of row significantly reduced seed cotton yields in two of the three experiments. Trash content of machine-harvested cotton was increased at densities of 64 and 128 prickly sida plants/15 m of row in one experiment. Staple length and grade of cotton were not affected by any weed density studied. Micronaire measurements of cotton were reduced at prickly sida densities of 64 and 128 weeds/15 m of row during 1972.
Responses of six morningglories (Ipomoeaspp.) and twoCassiaspp. to 13 preemergence applied herbicides were determined at two locations in southern Alabama. Pitted (I. lacunosaL.), cypressvine (I.quamoclitL.), and willowleaf morningglories (I. wrightiiGray) were readily controlled with metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one]; entireleaf [I. hederacea(L.) Jacq. var.integriusculaGray], tall [I. purpurea(L.) Roth.], and ivyleaf morningglories [I. hederacea(L.) Jacq.] were not controlled. Norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone] controlled cypressvine morningglory, but did not adequately control the other morningglory species. Perfluidone {1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide} gave acceptable control of cypressvine and willowleaf morningglories, but gave poor control of other morningglory species. Sicklepod (C.obtusifoliaL.) was controlled better than coffee senna (C.occidentalisL.) with 2.2 kg/ha diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and 2.2 kg/ha cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl]amino]-2-methylpropionitrile} controlled sicklepod better than coffee senna at one location each. Oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] was more effective in controlling coffee senna than sicklepod. Induction of population shifts toward incidental species of these genera seems unlikely based on the herbicides included in these experiments. In most cases the incidental species were more readily controlled than the prominent weed species.
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