Epidemic Forecast And Yield Loss Estimate On Alfalfa Common Leaf Spot Disease

Common Leaf Spot of Alfalfa (Medicago sativa L.) caused by Pseudopeziza medicaginis (Lib.) is the most common and serious disease occurred among varieties of Medicago. This disease in Alfalfa can occur throughout the growing period, often caused by a larger loss of forage yield, hay and seeds , as well as lower-quality. At present, the main means of prevention and treatment is chemical pesticide spraying, but its addition to the amount of excess waste caused by economic, but also brought about serious problems such as environmental pollution. In this study, projections from the disease point of view epidemic in the occurrence of the alfalfa leaf spot observation and study of the laws on the basis of information combined with the calendar year, the establishment of the alfalfa leaf spot prediction model meteorological factors, and through the analysis of disease and the resulting the relationship between yield loss, the establishment of a yield loss estimation model acicola. The main findings are as follows:1. Through 2007 and 2008 two years of alfalfa common leaf spot in Beijing for the systematic investigation of the occurrence, combined with the calendar year occurred in the history of the disease, the study of meteorological factors and the relationship between the incidence of alfalfa common leaf spot: When the relative humidity reached 58 %～75 %, the daily average temperature in the 15～30℃, ten days temperature in the 10. 2～15. 2℃, leaf spots began prevalence; When the temperature reached 16～17℃, relative humidity reached 79 %～97 %, caused by the disease prevalence on a few days. The promotion of the disease occurred condensation precipitation. Alfalfa common leaf spot in Beijing for annual incidence is in mid to late July; in mid-August on, when more rain, a rapid increase in condition to enter the peak incidence, in late September to early October as the drop in temperature gradually weakened condition.2. Based on the law of Alfalfa common leaf spot occurred epidemic, the affecting of the Alfalfa common leaf spot prevalence of the relevant meteorological factors carried out the regression analysis. A prediction model of a popular disease of alfalfa common leaf spot in Beijing area was set up. Y=-48.465+0.152X1+0.599X2-0.019X3, and the model prediction accuracy performed the test. Its forecast of 7d in Beijing of the disease index reached 91.34% accuracy.3. Through the investigation of leaf disease index in seven different disease-resisitant kinds of Alfalfa varieties and the yield loss assessment. Studied the relationship between the disease index(x) and yield loss rate(y). Clearly the relationship between the disease index and yield loss rate is positive correlation.Established three equations of yield loss forecast respectively,the regression mathematical expression is:Disease susceptible variety Y=6.145+1.263X; Disease medium-infected variety Y=3.429+1.550X; Disease tolerant variety Y=1.780X-0.957...