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LIFE STUDIES AND CONTROL OF SUNFLOWER
Abstract
Research investigating sunflower (Helianthus annuus L.) allelopathy, competition, and control and herbicide absorption, translocation, and metabolism in sunflower was conducted in the laboratory, greenhouse, and field during 1978 through 1980. In the field, soybeans {Glycine max (L.) Merr. 'Elf' and 'Amsoy 71'} required 4 to 6 weeks of sunflower-free competition for maximum yields. Competition boxes in the greenhouse showed that soybean height, fresh weight, and dry weight were significantly reduced at certain soybean and sunflower population densities from light, soil, and light + soil (full) competition. Sunflower height was not significantly reduced but fresh and dry weights decreased significantly when plant population was increased to three or four soybean and sunflower plants per compartment with light and full competition. A 2% or greater concentration of ground, mature, sunflower leaves in Sharpsburg silty clay loam (Typic Arguidoll) reduced emergence, height, fresh weight, and dry weight of soybeans, sorghum {Sorghum bicolor (L.) Moench 'G-265GBR'}, and sunflower itself. Sunflower stem and branch powder had similar effects but was less phytotoxic than the leaf powder on the three species. Phytotoxic root exudates were noted in experiments involving hydroponic nutrient solution and soil in which sunflower had previously been grown. Plant height, fresh weight, and dry weight were significantly reduced for all three plant species (sorghum, soybeans, and sunflower). However, only sunflower emergence was significantly decreased in these root exudation experiments. Bentazon {3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide} and bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) selectively controlled sunflower in soybeans when applied postemergence at sunflower heights of 5 to 10 cm. Use of these herbicides in combination at lower than recommended rates of each alone reduced control costs as compared with bentazon alone and soybean injury caused by bromoxynil. Benazolin (4-chloro-2-oxobenzothiazolin-3-ylacetic acid) used in combination with either bentazon or acifluorfen (5-{2-chloro-4-(trifluoromethyl)phenoxy}-2-nitrobenzoic acid) did not give better sunflower control than when bentazon or acifluorfen was used alone. Metribuzin provided better selective control of sunflower in soybeans when applied preplant incorporated than when applied preemergence due to the requirement of rainfall for activation in the preemergence mode of application. Use of the roller applicator to apply glyphosate {N-(phosphonomethyl)glycine} resulted in moderate control of heavy infestations of sunflower in soybeans. The roller applicator should not be used as a primary method of sunflower control in soybeans but could be used for controlling sunflower escapes. In laboratory experiments, ('14)C-bentazon was absorbed significantly faster and in greater quantities when a surfactant (alkylaryl polyglycol ether) was used with the herbicide treatment than when no surfactant was included. Autoradiographs and radioassays of sunflower plant parts revealed that the surfactant facilitated acropetal movement of ('14)C-bentazon in sunflower. Bentazon applied without the surfactant remained in the treated leaves. Basipetal movement was not a major translocative pathway for ('14)C-bentazon in sunflower. Forty percent of the absorbed ('14)C-bentazon was metabolized to a methanol soluble metabolite 3 days after treatment, as detected with high pressure liquid chromatography and liquid scintillation counting. Thin layer chromatography further substantiated the presence of a ('14)C-bentazon metabolite.
Subject Area
Agronomy
Recommended Citation
IRONS, STEPHEN MALCOLM, "LIFE STUDIES AND CONTROL OF SUNFLOWER" (1981). ETD collection for University of Nebraska-Lincoln. AAI8118163.
https://digitalcommons.unl.edu/dissertations/AAI8118163