Effects of Environmental Factors and Cultural Practices on Parasitism of Alfalfa by Ditylenchus dipsaci


  • G. D. Griffin


Cool humid weather enhanced development and reproduction of Ditylenchus dipsaci in alfalfa in laboratory and field studies in Utah. Relative humidity and nematode reproduction were positively correlated (P 0.05), whereas air temperature and nematode reproduction were negatively correlated (P 0.05). The greatest number of nematodes per gram of alfalfa tissue was found in nondormant Moapa alfalfa tissue at St. George during April, whereas the greatest numbers of nematodes were found in dormant Ranger alfalfa in June at West Jordan and Smithfield. There was 100% invasion of both resistant Lahontan and susceptible Ranger alfalfa plants at soil moisture levels of 61-94% field capacity. Fall burning of alfalfa to control weeds reduced, and spring burning increased, the incidence of invaded plants, nematodes per gram of plant tissue, and the mortality of susceptible Ranger (P 0.01) and Moapa (P 0.01) alfalfa plants over that of plants in nonburned control plots. Fall burning also reduced and spring burning increased the incidence of invaded plants (P 0.05), but had no influence on nematodes per gram of plant tissue or the mortality of resistant Lahontan and Nevada Synthetic XX alfalfa over those of plants in control plots. Key words: alfalfa stem nematode, air temperature, mortality, relative humidity, reproduction, resistance, soil moisture, susceptibility, Ditylenchus dipsaci, Medicago sativa.