Study On Chemical Control Of Alfalfa Rust Disease

Alfalfa is the most widely distributed, high yield and quality forage in the world.With the development of alfalfa industry, the area of alfalfa planting is expandingunceasingly, alfalfa disease problem is more and more serious, and cause seriouseconomic losses of production. But now there is no special fungicides for alfalfa rustdisease on the market, the prevention and treatment are mainly used by agriculturalmeasure in some area. In order to get better prevention and control, in the studydifferent fungicides were selected and compounded for alfalfa rust disease. At first,the biological characteristics of uredospore and toxicity measurement of differentfungicides were studied by using spore germination method; the sensitive of differentfungicides and compound with fungicides and synergy were studied by using themethod of potted inoculation; the dispensing synergy effect of the greenhousescreening were studied by means of field efficacy test method; Though statistic dataof production, ratio of stem leaf and plant height have analyzed damage situation ofalfalfa rust, and studied allow loss rate and the prevention and control of economicthreshold. The results are as follows:1. The results showed that the urediospore can only germinate under theenvironment of high relative humidity, and below100%relative humidity, in5~30℃, especial in the20~25℃, but over30℃or below5℃basic notgermination; Light and1%glucose solution has promoting the effect of the sporegermination.2. Through toxicity measurement in vitro, the results showed that pyraclostrobinand azoxystrobin have produced best effect, the EC50were0.0401mg/L and0.0681mg/L, respectively.3. The test results indicated that azoxystrobin was the most sensitive and EC50was1.8809mg·L-1while thiophanate-methyl was the worst and EC50was747.0022mg·L-1. According to the different sterilization mechanism of fungicidescompound principle,9kinds of combination, azoxystrobin mixed with tebuconazole, when the mixture was1:9can produced an additive effect, the restare produced synergistic effect and synergistic effect of5:1ratio mixture was thestrongest, efficiency coefficient was4.9684; Azoxystrobin mixed withdimethomorph,1:3ratio mixture is the strongest synergies and efficiencycoefficient was5.1114, but9:1ratio mixture produced antagonism effect;Azoxystrobin mixed with mancozeb,1:7ratio mixture was the more obvioussynergies and efficiency coefficient was4.5757. Pyraclostrobin mixed withdifenoconazole, synergistic of1:5ratio mixture was the strongest synergy actionand efficiency coefficient was5.2276; Pyraclostrobin mixed with chlorothalonil,synergistic of1:7ratio mixture was the most obvious, its efficiency coefficientwas5.8058.4. Based on the field experimental study, the results showed that there was only twodispensing create synergy, azoxystrobin compounded with mancozeb, theeffective dose was80g/hm2,400g/hm2by1:5, the control effect was87.06%;pyraclostrobin compounded with chlorothalonil, the effective dose was100g/hm2,500g/hm2by1:5, produce synergistic effect, the control effect of90.85%.5. Through calculation to cost of the prevention and control and loss rate, studieshave shown alfalfa rust allowed loss rate is5.56%when control efficiency isabout80%; established economic threshold model of alfalfa rust prevention andcontrol and the threshold value, economic threshold of prevention and controlwas3.4%.6. The different severity of alfalfa rust disease have a significant impact on the plantheight, stem leaf ratio and yield loss rate, as the disease aggravating, the plantheight have a tendency of dwarf while the stem leaf ratio and yield loss rate haveincreased tendency.