Effect Of Walnut-Wheat Intercropping On The Occurrence Of Main Wheat Pests

Southern Xinjiang is located in the southern edge of the Takelamagan desert.In this area,ecological environment is fragile,arable land is less per capita,and poor population is high.Since the beginning of this century,the adjustment of agricultural structure has been carried out in southern Xinjiang to raise farmers’ income and relieve farmers’ poverty as soon as possible.Walnut,jujube,and apricot intercropping with wheat,corn,and other crops has been gradually developed for nearly 20 years in southern Xinjiang.The walnut-wheat intercropping is one of the main planting patterns.Walnut trees have a certain influence on light,temperature,humidity,wind direction,and wind speed in the wheat fields because they have big canopy.So,there are difference in environmental conditions between walnut-wheat intercropping and wheat monoculture.In addition,as the walnut trees are planted in wheat fields and small machines are used for farming in walnut-wheat intercropping,the soil tillage depth and fineness of soil environment also have some differences with the wheat monoculture.Under this influence,the occurrence and damage of main diseases,insect pests,weeds and other harmful organisms in the field of walnut wheat intercropping will also change accordingly.Objevtives of this study were:investigate the effect of walnut-wheat intercropping on main pests powdery mildew and leaf rust diseases,insect pest aphid,and weeds in wheat fields.Through successive five years of research,the main results are as follows:The effect of walnut-wheat intercropping on wheat powdery mildew was obviously affected by 3 aspects.First,the onset time of powdery mildew was early,from May 16.2012 to May 1,2016.Second,the disease index of wheat powdery mildew of walnut-wheat intercropping was significantly higher than that of wheat monoculture.Third,the damage of powdery mildew in walnut-wheat intercropping was aggravated.The occurrence period of wheat leaf rust in walnut-wheat intercropping was basically consistent with monoculture crop.The occurrence degree and the epidemic rate of wheat leaf rust was lower in walnut-wheat intercropping than in wheat monoculture,and the peak of disease index also was significantly lower than in wheat monoculture.There was no significant difference between different years in walnut-wheat intercropping.However,the disease index of wheat leaf rust had significant difference among different years in wheat monoculture.Compared with wheat monoculture,the walnut-wheat intercropping was not beneficial to the occurrence and damage of wheat leaf rust.Results showed that the appearance of wheat aphid Sitobion avenae in wheat fields was earlier in walnut-wheat intercropping than that in wheat monoculture.The aphid occurred faster and had higher reproduction rate in walnut wheat intercropping than in wheat monoculture.The occurrence peak per plant also was much higher in walnut wheat intercropping thanin wheat monoculture.Wheat aphid is the main pest in winter wheat field in southern Xinjiang.The annual occurrence of wheat aphid changed greatly.From 2012 to 2016,the number of aphids in 2012 and 2013 was significantly higher than that in other years after successive intercropping for five years.The results showed that 39 weed species belonged to 33 genera of 14 families in the winter wheat field in southern Xinjiang(8 species of compositae,7 species of gramineae,5 species of Chenopodiaceae,3 species of cruciferous,3 species of polygonaceae,and 3 species of legumes).The dominant weed species in walnut-wheat intercropping and wheat monoculture were similar,including Chenopodium serotinu,Echinochloa crus-galli,Descurainia sophia,Polygonum aviculare,Sclerochloa kengiana,Sonchus brachyotus,Malcomia africana,Cephalanoplos segetum,and Convolvulus arvensis.The damage degree of the dominant weeds had some differences.The damage of P.aviculare was more serious in wheat monoculture than in walnut-wheat intercropping.The density of S.brachyotus and M.africana was higher in walnut-wheat intercropping than in wheat monoculture.S.nigrum,A.theophrasti,and Taraxacum mongolicum,as regional dominant weed species,was more harmful in walnut wheat intercropping than in wheat monoculture.Amaranthus retroflexus,Phragmites communis,and Equisetum ramosissimum,as regional dominat weed species,was more harmful in wheat monoculture than in walnut-wheat intercropping.The weed species richness and diversity index was higher in walnut-wheat intercropping than in wheat monoculture.Through this systematic study,the damage characteristics,occurrence time,epidemic dinamics,and damage types of the major pests in the fields of walnut-wheat intercropping were identified.The findings will provide comprehensive technical support for the pest control in the wheat fields of walnut-wheat intercropping in the southern Xinjiang.