Graduate Thesis Or Dissertation
 

Factors affecting selective weedy rye (Secale sp.) control in winter wheat with the herbicide ethiazin

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  • Weedy rye (Secale spp.) is a weed in the winter-wheat- growing regions in the Pacific Northwest and surrounding regions. Ethiazin (4-amino-6-(1,1-dimethylethyl)-3- (ehtylthio)-1,2,4-triazine-5 (4H)-one) has shown selective control of weedy rye in the cultivar 'Stephens', (Triticum aestivum). Field, greenhouse, and outdoor pot experiments were conducted to determine factors influencing selectivity. Field studies were conducted in eastern Oregon in 1985-86 to determine the optimum timing and rate to apply ethiazin for weedy rye control, and also to see if the addition of metribuzin would increase rye control while reducing the ethiazin rate. Stephens wheat tolerated the herbicide treatments at all locations. Optimum timing for application was the 2-3 leaf stage of rye for two of the locations. Application at the 1-2 leaf stage was most effective at the remaining location. Rye control was enhanced with increasing ethiazin rate. The addition of metribuzin enhanced rye control at a lower rate of ethiazin. Wheat grain yields, above ground biomass, and culm number of wheat increased with increasing rye control. Greenhouse and outdoor pot studies were conducted in Pendleton and Corvallis, Oregon, through 1985-87, to identify factors influencing this selectivity. Uptake experiments indicated that rye is more sensitive to ethiazin through root uptake than through foliar uptake. In time-of-application studies conducted outdoors, best control was at the one-, two- , and three-leaf stage of rye. Control was lower at preemergence and the four-leaf stage. Depth of seeding did not affect sensitivity of rye to ethiazin. Immersing roots of wheat and rye seedings into ethiazin solution at various concentrations showed Stephens to be 13 times more tolerant than cereal rye to ethiazin. This indicates that selectivity between wheat and rye seen in the field is primarily due to physiological differences. From a management standpoint, this is greatly preferable to selectivity based on differences in retention on the foliage, rooting depth, crown depth, and other morphological factors. Weedy rye appears to be taxonomically different from the cultivated species (Secale cereale). Wild and weedy rye were equally sensitive to ethiazin when tested in a solution bioassay.
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