Fumigation of tomato (Lycopersicon esculentumMill. ‘Sheyenne’) with low levels of O3had little effect on root absorption, translocation, or conversion of diphenamid (N,N-dimethyl-2,2-diphenylacetamide) to water-soluble conjugates. However, the proportion of specific conjugates was markedly altered in O3-fumigated plants. Twenty-four hours after treatment, the predominant conjugates formed in nonfumigated and fumigated tomato were the β-glucoside (MDAG), and the β-gentiobioside (MDAGB), respectively, ofN-hydroxymethyl-N-methyl-2,2-diphenylacetamide. The ratio MDAG:MDAGB was 8.2:1.0 in nonfumigated tissue and 0.6:1.0 in O3-fumigated tissue. This marked shift toward production of the more polar MDAGB was accompanied by a trend toward increased production of methanol-insoluble residues. A compound having limited stability was extracted from tomato; its probable structure wasN-hydroxymethyl-N-methyl-2,2-diphenylacetamide (MODA). It is a postulated intermediate in the formation of MDAG and MDAGB from diphenamid.

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The plant pathogenic fungusColletotrichum coccodes(Cc) and the plant growth regulator thidiazuron (TDZ) were evaluated in Maryland and Quebec for velvetleaf control in ‘Williams' and ‘Maple Arrow’ soybean. TDZ was applied at 0, 0.1, 0.2, 0.3, and 0.4 kg ai/ha alone or was combined with Cc at 109spores/m2when velvetleaf was at the 1- to 2-leaf (Trial 1) or 4- to 6-leaf (Trial 2) growth stages. Velvetleaf control increased with TDZ rate, and TDZ combined with Cc further increased control. TDZ reduced velvetleaf biomass and height, and Cc increased velvetleaf mortality. In Quebec, Cc also reduced the biomass of velvetleaf treated in Trial 1 and interacted positively with TDZ at this growth stage. Cc nearly halved the rates of TDZ required for 90 and 75% mortality of velvetleaf treated at the 1- to 2-leaf and 4- to 6-leaf stages to 0.09 and 0.12 kg/ha, respectively, in Quebec. Cc similarly lowered the rate of TDZ required for 75% stand reduction of velvetleaf in Trial 1 to 0.17 kg/ha in Maryland. Cool wet weather in Quebec contrasted with warm, dry weather in Maryland. Soybean biomass and yield were increased significantly by treatment with TDZ plus Cc in Trial 1 at both locations.

The time course of diphenamid (N,N-dimethyl-2,2-diphenylacetamide) metabolism in tomato (Lycopersicon esculentumMill. ‘Sheyenne’) was altered by fumigation with 30 pphm (parts per hundred million) of O3. After 2 days 70% of the absorbed diphenamid was metabolized in controls compared with 83% in fumigated plants. Concentrations ofN-methyl-2,2-diphenylacetamide (MMDA) were equivalent in both fumigated and control plants. Less glucoside conjugate (MDAG) was present in fumigated plants 2 to 4 days after treatment than in the control plants. Gentiobioside conjugate (MDAGB) increased rapidly in fumigated plants after 0.5 day but not in control plants until after 2 days. Loss of diphenamid from aerated solution was demonstrated. A scheme for diphenamid metabolism is proposed.