Klose Susanne, Ajwa Husein A, Browne Greg T, Subbarao Krishna V, Martin Frank N, Fennimore Steve A, Westerdahl Becky B
Department of Plant Sciences, University of California Davis, 1636 East Alisal Street, Salinas, CA 93905, USA.
USDA-ARS, Crops Pathology and Genetics Research Unit, Department of Plant Pathology, University of California Davis, Davis, CA 95616, USA.
Plant Dis. 2008 Nov;92(11):1537-1546. doi: 10.1094/PDIS-92-11-1537.
Metam sodium (sodium N-methyl dithiocarbamate, metam-Na) is widely used in agricultural and floricultural production for controlling soilborne plant pathogens, parasitic nematodes, and weeds. It undergoes rapid decomposition to the biocide methyl isothiocyanate (MITC) in moist soils. In this study, the efficacy of 12 concentrations of metam-Na (10 to 2,650 μmol kg soil) to control seeds or tubers of five major weed species, three soilborne pathogens, and one parasitic nematode was evaluated in a sandy loam soil under controlled conditions. Soils were exposed to the fumigant in microcosms for 24 h at 10 and 20°C. Generation and dissipation curves of MITC in soil under controlled conditions showed that MITC concentrations in soils were highest 2 h after metam-Na application and decreased steadily over the 24-h incubation period. After 24 h, remaining MITC concentrations in soil microcosms at 10 and 20°C were 53 and 38% of the original amount applied, respectively, indicating a 20% reduction in MITC dissipation at the lower soil temperature. Logistic dose-response models were used to estimate the effective concentration necessary to reduce soil pest viability by 50 (LC) or 90 (LC) percent under both temperatures. Seed of Portulaca oleracea, with LC values of ≤1,242 μmol kg soil, was the most sensitive to soil fumigation with metam-Na, followed by Polygonum arenastrum with LC values of ≤1,922 μmol kg soil. At 10°C fumigation temperature, metam-Na at the highest dose tested in this study, 2,650 μmol kg soil, was not sufficient to achieve adequate control of Stellaria media and Malva parviflora seed and Cyperus esculentus tubers. Weed control efficacy (average reduction in LC values) of metam-Na was between 25 and 60% higher if soils were fumigated at 20°C compared with 10°C, with the exception of M. parviflora. Phytophthora cactorum and Pythium ultimum were more sensitive to soil fumigation with metam-Na (LC ≤ 165 μmol kg soil) than Verticillium dahliae (LC ≤ 737 μmol kg soil). The nematode Tylenchulus semipenetrans was highly sensitive to soil fumigation with metam-Na (LC ≤ 98 μmol kg soil), and the efficacy of control increased by 30% if soil was fumigated at 20°C compared with 10°C. In this sandy loam soil, metam-Na at a concentration of 850 μmol kg reduced the viability of Portulaca oleracea and Polygonum arenastrum seeds, C. esculentus tubers, and all soilborne pathogens and parasitic nematodes tested by 90% at 20°C after 24 h exposure. These results indicate that metam-Na can provide effective pest and disease control at maximum label rate for the commercial formulation, but there was a reduction in efficacy at low temperature.
威百亩（甲基二硫代氨基甲酸钠，威百亩 - Na）广泛用于农业和花卉生产中，以控制土壤传播的植物病原体、寄生线虫和杂草。在潮湿土壤中，它会迅速分解为杀生物剂甲基异硫氰酸酯（MITC）。在本研究中，在可控条件下，于砂壤土中评估了12种浓度的威百亩（10至2650 μmol/kg土壤）对5种主要杂草种子或块茎、3种土壤传播病原体及1种寄生线虫的防治效果。土壤在微型试验装置中于10℃和20℃下暴露于熏蒸剂24小时。可控条件下土壤中MITC的生成和消散曲线表明，施用威百亩后2小时土壤中MITC浓度最高，并在24小时培养期内稳步下降。24小时后，10℃和20℃下土壤微型试验装置中剩余的MITC浓度分别为施用量的53%和38%，表明较低土壤温度下MITC消散减少了20%。使用逻辑剂量 - 反应模型来估计在两种温度下将土壤害虫活力降低50%（LC₅₀）或90%（LC₉₀）所需的有效浓度。马齿苋种子对威百亩土壤熏蒸最敏感，LC值≤1242 μmol/kg土壤，其次是沙生蓼，LC值≤1922 μmol/kg土壤。在10℃熏蒸温度下，本研究中测试的最高剂量2650 μmol/kg土壤的威百亩不足以充分防治繁缕和小花锦葵种子以及香附子块茎。与10℃相比，若在20℃下熏蒸土壤，威百亩的杂草防治效果（LC值平均降低）高25%至60%，小花锦葵除外。恶疫霉和终极腐霉对威百亩土壤熏蒸（LC≤165 μmol/kg土壤）比大丽轮枝菌（LC≤737 μmol/kg土壤）更敏感。半穿刺线虫对威百亩土壤熏蒸高度敏感（LC≤98 μmol/kg土壤），与10℃相比，20℃熏蒸土壤时防治效果提高30%。在这种砂壤土中，850 μmol/kg浓度的威百亩在20℃下暴露24小时后，可使马齿苋和沙生蓼种子、香附子块茎以及所有测试的土壤传播病原体和寄生线虫的活力降低90%。这些结果表明，威百亩以商业配方的最大标签剂量可提供有效的病虫害防治，但在低温下效果会降低。
