Study On The Critical Period Of Chemical Control Of Potato Early Blight In Zhangbei,Hebei

The purpose of this study is to determine the critical period for the use of chemical agents to control potato early blight through field trials,and to provide a theoretical basis for high-efficiency chemical control.The field trials were conducted simultaneously with both precocious(Favorita)and mid-late maturing(Shepody),all using the same chemical and the same sprayed interval,through a weekly systematic survey of field early blight.Compare the different numbers of chemical or the same chemical in different periods to the control effect on disease prevalence and the effect on potato tuber yield and commodity rate.Two trials were conducted during the growing season in 2017 and 2018.In the first growing season(2017),the first sprayed was carried out at different times after the occurrence of potato early blight in the field,to determine the critical period of first application of pesticide.In the second growing season(2018),all treatments were performed for the first time in the critical period(Sporadic lesions in the field-1%disease severity)of the first application of pesticide.Different treatments have different follow-up spray times of pesticide.The main results in the test are as follows:1.Field disease surveys showed that early maturing variety and mid-late maturing variety of potato in Zhangbei area of Hebei Province began to develop early blight from late June to early July.The seasonal epidemic curve of the disease is roughly "S" type from late July to early august,it is a critical period for the disease to be “lightly transferred to heavy”.2.The results of field disease prevention and control tests for two consecutive years showed that the first application of pesticides at different times after the occurrence of potato early blight in the field had a significant difference in the whole growing season.At the beginning of the disease,sporadic lesions began to appear in the field(The severity of the disease is less than 1%).The first spraying has the best effect on the prevention and control of the disease in the whole growing season.With the delay of the first sprayed,the prevention and control effect is reduced in turn;in the case of the same chemical and the interval,the first time of the chemical sprayed in the early stage of the disease is significantly better than the delay first chemical administration time;in the case of suitable first-time chemical,one sprayed the final severity of the disease on the early-maturing variety can be controlled to less than5%(Interval 10d).The two times chemical sprayed can control the damage of thepotato early blight of mid-late maturity(the final disease severity is 5% or less).3.Considering the effects of disease prevention and yield increase(maintenance of production),for early maturing varieties and mid-late maturing varieties.The critical period for the first time of chemical control of the disease of potato early blight is beginning to appear in the field or sporadic lesions begin to appear in the field.In the general area of zhangbei,1-2 times of chemical use(interval 10 days)can control the damage of early-maturing varieties,and 2-3 times can control the damage of mid-late maturing varieties.