Graduate Thesis Or Dissertation

 

Foliar vs. root uptake of the herbicide Hoe 23408 in Italian ryegrass and wild oats Public Deposited

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  • HOE 23408 [methyl 2-[ 4-( 2, 4- dichlorophenoxy )phenoxy]propanoate] is a herbicide used to selectively-control Italian ryegrass (Lolium muitiflorum Lam.) and wild oats (Avena fatua L.) in wheat. The objective of this research was to compare the relative importance of foliar and root uptake of the herbicide in these two weed species. Factors such as plant biotype, stage of plant growth, soil type, irrigation type, and amount of soil moisture were examined. Plants were grown in plastic pots in the greenhouse with a 12- hour day, 12-hour night schedule. HOE 23408 (38% a.i. emulsifiable concentrate) was applied using an overhead variable-speed sprayer calibrated to deliver 309 L/ha. The herbicide was applied at three placement sites: foliage only, soil only, and foliage plus soil. Foliar placement was accomplished by protecting the soil with a 1.5 cm layer of perlite prior to spraying. This layer was removed when dry. Soil only application was administered by pouring a 25 ml solution of the herbicide directly onto the soil. The combination treatment was sprayed with neither area protected. Symptoms developed within 2 to 4 weeks from the day of treatment. Fresh weights, visual ratings of injury, and dry weights were obtained to assess injury. Fresh weights gave the best injury estimate and were converted to percent fresh weight reduction prior to analysis. Five replications were used in each experiment. Both foliar only and soil only applications of the herbicide caused injury to both species. Italian ryegrass was more sensitive to HOE 23408 than wild oats. HOE 23408 was applied at rates of .56, 1.12, 1.68, and 2.24 kg/ha. Injury increased with increasing rate in all placement treatments. The effect of the herbicide on ryegrass and wild oats was examined under conditions of New Zealand and western Oregon. In New Zealand, the high organic matter Canterbury Plains silt loam greatly reduced soil activity of the herbicide. 'Tama' ryegrass, a rapidly growing New Zealand variety, was found to be more sensitive to foliar application than the western Oregon biotype. Ryegrass was slightly more susceptible to the herbicide at the one- to two-leaf stage than at the three- to four-leaf stage. Ryegrass and wild oats were grown in western Oregon using Woodburn silt loam (3.5% 0.M.), Newberg sandy loam (1.7% O.M.), and silica sand (0.5% O.M.). Injury from a 1.12 kg/ha application of the herbicide decreased with increasing organic matter content. No differences were noted for foliar applications of the herbicide in the different soil types. Placement effects were examined under two irrigation types: subsurface and overhead. No placement x irrigation interaction was noted. Plants subjected to subsurface irrigation grew more rapidly, and consequently, the overall injury was greatest in these plants. Two studies were conducted with ryegrass grown under various soil moisture conditions: 120% Field Capacity (F.C.), 96% F.C., 60% F.C., and 32% F.C. Neither foliage only nor soil only placements were affected by soil moisture. However, HOE 23408 activity in the combination treatment was significantly reduced under low soil moisture conditions. Ryegrass and wheat were grown in quart size glass Mason jars filled with nutrient solution. The objective of this study was to determine if root inhibition could be caused by either placement of HOE 23408. The herbicide was applied either to the foliage or to the nutrient solution. Measurements of the longest root were taken daily. Root growth was severely inhibited only when the roots were exposed to the herbicide, not when the foliage was treated.
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