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Winter wheat (Triticum aestivum L.) seed is often planted deeply (>3 in.) into stubble-mulch fallow in the semi-arid Pacific Northwest (PNW). Stand establishment is affected by factors that influence the rate of seed germination and coleoptile growth. Systemically translocated triazole and imidazole fungicide seed treatments were compared for effects on seedling emergence under conditions of deep seed placement and variable seed-zone moisture in stubble-mulch fallow systems. Fungicides included RTU Vitavax Thiram (carboxin [2,3-dihydro-5-carboxanilido-6-methyl-1,4-oxathiin] + thiram [tetramethylthiuram disulfide]), Dividend (difenoconazole [1-(2-[4-(4-chlorophenoxy)-2-chlorophenyl]-4-methyl-1,3-dioxolan-2-yl-methyl)-1H-1,2,4-triazole]), Raxil Thiram (tebuconazole [α[2-(4-chlorophenyl)ethyl]-α-(1,1-dimethylethyl)-1H1,2,4-triazole-1-ethanol] + thiram), NuZone and Flo-Pro IMZ (imazalil [1-(2-(2,4-dichlorophenyl)-2-(2-propenyloxy)ethyl)-lH-imidazole]), and Apron (metalaxyl [N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-alanine methyl ester)]). Gaucho (imidacloprid [1 [(6-chloro-3-pyridinyl)methyl]-N-nitro-2-imidazoli-diniminel), a seed-treatment insecticide, was applied in some experiments. Seven field and three greenhouse experiments were performed from 1993 to 1995. Emergence in the field tended to be superior for seed treated with Dividend, alone or mixed with Apron, in plantings made from 1- to 5-in. deep into soil with 5 to 17% seed-zone water content and at 71 to 80°F. RTU Vitavax Thiram had variable effects on seedling emergence. NuZone and Raxil Thiram, alone or mixed with Gaucho, generally delayed emergence when treated seed was planted at depths more than 2 in. In the greenhouse, treated seed was planted at 1-in. depth into moist (7, 10 or 15% w/w), warm (75°F) silt loam overlain by 4-in. of dry silt loam, simulating a planting at 5-in. depth into stubble-mulch fallow during September. Emergence of Dividend-treated seed at each soil moisture content was usually more rapid than for other treatments, including seed planted without fungicide treatment. This research demonstrated that emergence of winter wheat planted deeply into stubble-mulch fallow is often improved when seed is treated with Dividend compared with RTU Vitavax Thiram and, among the systemically translocated triazole fungicides, Dividend is a better choice than Raxil when planting depths exceed 2 in. |
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