Population Dynamics And Integrated Control Of Corn Spider Mites In Wuwei, Gansu

Corn spider mite generally breaks out widely, strongly and fast, which leads to difficulties of control and thus tremendous loss of production. In recent years, corn spider mite has occurred yearly in Gansu province, and has led to serious damage to corn industry and seed industry. It is now a typical "little bug triggered big problem". In this paper, the dynamics and a comprehensive chemical control of spider mite were studied with corn in Wuwei, Gansu.1. The population dynamics of spider mite were investigated in the fields of three different corn cultivars. It showed that spider mite distributed in an aggregate pattern at the vertical scale,and the intensity of gathering was related to density. Application of the optimal partition method showed that population dynamics of spider mite in the field could be divided into four stages,including early establishing(mid and late July), growing(late July to early August), peaking(mid August) and declining(after mid August) stages. The average density, crowding extent, tufted indicator and diffusion coefficient of the lower leaves were greater than those of the middle and upper leaves, suggesting that spider mite gathered mainly in the lower leaves at the early stages of corn growth and later translocated to the upper leaves gradually. So when spraying to control spider mite, we should pay more attentions to the lower leaves and the back of the leaves.2. The resistance to spider mite was studied in 10 different corn cultivars. It was found that all 10 cultivars would be injured by spider mite and only the self resistance could not help to maintain normal growth, achieving high yield and quality of corn production. Thus some useful and practical controls, i.e. agricultural, physical and chemical ways, should be hired to gain stable or even high production. Five corn cultivars showed higher yield of 1000 kg per mu, among them only three showed high resistance to spider mite.3. The controls of eight new acaricides on spider mite were evaluated in fields. Among them,1.8% avermectin EC, 15% pyridaben EC, 24% Spirodiclofen SC and 5% Fenpyroximate SC showed good and fast controls on spider mite with long duration. Thus they were ideal for quick control on corn spider mite density. The 5% hexythiazox EC and 5% Fenpyroximate SC showed a very long-term control on spider mite.The effectiveness of acaricides and fuming ways were investigated in the fields. The smoky acaricide which included 1.8% avermectin EC and 15%pyridaben EC, showed excellent control on spider mite with fast action and long duration, and thus was ideal for quickly and widely reducing spider mites. This combination was a good option to control spider mite of corn. Among differently fuming ways to control spider mite, toxic soil fumigation could kill spider mite quickly, reducing density, while fumigation with plastic bag reacted slowing and could work at the early stage of spider mite outbreak. In addition, corn stubble and cloth bag fuming ways either played roles in controlling spider mite with effectiveness between the former two ways.Conclusively, selection of reagents and ways to control spider mite during corn growing season should be scientific and rational, achieving the greatest effectiveness. Attentions should be also paid to the combinations of reagents and ways, retarding the formation of the tolerance of spider mite to reagents.