Effects Of Straw Centralize-Buried In Soil On Suevtval Dynamics Of Phytoalexin(Fusarium Graminearum Sehw.)and Stem-Borer(Chilo Suppressalis Walker)Larvae

Straw returning can take back large number of diseases and pests into soil, but it can effective reduce the crop pests source through deep ditch buried. This study was carried out with methods of pot experiments. From the point of reducing the diseases and pests, four different straw ditch-buried depths (5cm、20cm、35cm、50cm) and ck (straw mulched and rotary tillage returned) were set to study the effects of different return depths on summering survival rate of Fusarium graminearum, rice carrier rate, overwintering survival rate of stem borer and their unearthed behavior. Main results are as follows:1. The flooded time and return depths significantly affect the survival days and survival rate of Fusarium graminearum.In flooded condition, grain, straw and husk with Fusarium graminearum been centralize-buried, the Fusarium graminearum can survive3-6d,6-12d and15-18d respectively. The straw with gibberella return into soil can cause the soil contaminated. With return days and depths increased, the survival days and survival rate reduced. The flooded time and return depths significantly affect the survival days and survival rate of Fusarium graminearum.The rice plant was infected under the treatment of straw mulching, rotary tillage returning and5cm buried, but not under20cm,35cm,50cm buried treatments. It shows rice plant was easily infected, so as to increase the number of colonies in the soil. But when buried over20cm, the colonies were reduced. In addition, the base stem and grain of rice have a high carrier rate, it shows that straw mulching, rotary tillage returning and5cm buried will increase the cross-infection phenomenon of Fusarium graminearum in wheat and rice. 2. Straw returning depth can significantly affect the larvae survival rate and larvae’ spring unearthed behavior.Straw returning depth was negatively correlated with the stem borer overwintering survival rate. The deeper of the buried straw, the lower survival rate of stem borer. The larval mortality will up to60%or more when the depth is over20cm. Spring straw returning will more effectively suppress the amount of the overwintering stem borer than the autumn straw application. During straw application, the minimum duration time of unearthed larvae from the overwintering stem borer was Od, and the maximum was up to85d. The peak activity time of larvae was mainly concentrate in the5am to7am and8pm to10pm, while straw returning concentrated on12am to2pm.3. Environmental factors can significantly affect the larvae survival rate and larvae’ spring unearthed behavior.The larvae survival rate and unearthed law of overwintering stem borer were influenced by the following environmental factors, buried depths, temperature, amount of straw, soil bulk density, precipitation, etc. Among these factors, buried depth was the most crucial factor, which showed that the depth of straw returning can significantly affect the larvae survival rate and larvae’ spring unearthed behavior.4. Straw returning depth can significantly affect egg masses of the first generation of overwintering striped rice borer and its ETUnder the straw centralize-buried returning in soil, the results of comparison between the egg masses of the first generation of stem borer and its ET are as follows:the treatment of straw mulching returning:14850No·hm-2>2055,No·hm-2,5cm:11295No·hm-2>2205No·hm-2,20cm:8865No· hm-2>2055No·hm-2,35cm:810No·hm-2<1980No·hm-2,50cm:0No·hm-2<1965No·hm-2. All these showed that when the depth of straw returning up to35cm, the larvae of the overwintering stem borer could be effectively eliminated.