Graduate Thesis Or Dissertation
 

Persistence of prodiamine and norflurazon herbicides in soil and their activity on alfalfa rotational crops

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  • Norflurazon [4-chloro-5-(methylamino)-2(3-(trifluoromethyl) phenyl)- 3(2H)- pyridazinone] and prodiamine (N3, N3-di-n-propy1-2,4- dinitro-6-(trifluoromethyl)-m-phenylenediamine) are two herbicides being considered for weed control in alfalfa. Rotational crops following alfalfa may be sensitive to residues of these herbicides. Studies were conducted in Oregon and Washington to examine the soil persistence and activity of these herbicides on alfalfa rotational crops. Norflurazon at 1.6 and 2.4 lb ai/a and prodiamine at 1.0 and 2.0 lb ai/a were applied during the fall of 1987 or spring of 1988 in Oregon and Washington. Soil samples were collected from plots treated with the highest herbicide rate when rotational crops were planted and again at harvest during 1988 and 1989. These samples were chemically analyzed for herbicide residues. Rotational crops were planted 3 and 15 months after treatment (MAT) in the spring-applied sites and 6 and 18 MAT in the fall-applied site to assess the activity of the herbicides. For both soils and application timings, dissipation of norflurazon and prodiamine was characterized by a rapid initial loss followed by slow disappearance of the remaining herbicide. The logarithm of herbicide loss was a linear function of days after treatment (DAT). The rate of norflurazon loss was not different among locations. Degradation of prodiamine tended to be slowest in the fall-applied site in Washington, followed in turn by the springapplied site in Washington and the Oregon site (p = 0.25). Relative crop sensitivity to norflurazon, ranked from most sensitive, was barley > spring wheat > field corn > potatoes > and beans. Crop sensitivity to prodiamine was ranked as field corn > barley > spring wheat > potatoes > and beans. Injury to barley and spring wheat planted 18 MAT resulted from residues of norflurazon applied at the high rate. Field corn and potatoes were injured significantly only when planted 3 and 5 MAT. No significant norflurazon injury was observed to beans during any planting interval. Prodiamine caused injury to field corn, barley, and spring wheat when planted 18 MAT. No injury to potatoes and beans was observed during any planting interval. Prodiamine was more toxic to susceptible crops at the low concentrations than norflurazon. Severe corn injury resulted from prodiamine residues of 0.01 ppm at all locations. The norflurazon and prodiamine residues from chemical analyses corresponded well with the observed injury from each of the plant-back species when soil characteristics were considered. Similar amounts of norflurazon and prodiamine residues were detected in the fall- and spring-applied sites in Washington during the 3 and 5 MAT sample interval. However, spring wheat and potato injury were greater in the fall-applied trial. More precipitation fell immediately after the fall application, moving the herbicides into soil solution and the crop root zone more readily.
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