Monitoring Of Wheat Powdery Mildew Under Different Nitrogen Application Levels Using Remote Sensing And The Reduction Application Of Fungicides

Wheat powdery mildew is one of the most important diseases in wheat production.Through three years of field trials from 2017-2019,the correlation relationships between the disease index of wheat powdery mildew and the canopy spectrum under different nitrogen application levels at anthesis,early milk,and late milk stage of wheat was analyzed,and the relationship models between disease index and spectral parameters were established.Further more,the correlation relationships between the yield,1000-kernel weight and the spectral parameters at anthesis,early milk,and late milk stage was analyzed,and the relationship models of yield,1000-kernel weight based on spectral parameters were established.In addition,the differences of the estimated models of disease index,yield,and 1000-kernel weight based on the spectral parameters at anthesis,early milk and late milk stage under different nitrogen fertilizer application levels were compared.Besides,the effect of different nitrogen application levels on the control efficiency of 25%ethirimol SC on wheat powdery mildew was analyzed by using the random coefficient mixed models.These results provide the basis for the application of remote sensing technology in monitoring on wheat powdery mildew and estimating yields,and the reduction of fertilizers and fungicides in application.The main conclusions obtained in this study were as follows:The results indicated that NIR,DVI,SAVI,and TVI can be used to monitor the disease index of wheat powdery mildew under different nitrogen fertilizer application levels at anthesis,early milk and late milk stage in three years of field trials.The estimation models of wheat powdery mildew disease index based on NIR,DVI,SAVI,TVI spectral parameters under different nitrogen fertilizer application levels were established.The slope and intercept of disease index estimation models were diverse in different years and growth stages.The spectrum parameter d?red,SDr,NIR,DVI,SAVI,TVI,and NRI are available to estimate the yield and 1000-kernel weight after wheat powdery mildew diseases at anthesis,early milk and late milk stage under different nitrogen application levels.Further more,the relationship models were established based on these spectral parameters to estimate the wheat yield and 1000-kernel weight after wheat powdery mildew infected.The comparative analysis of these models based on the same spectral parameters showed that the slopes and intercepts of yield or 1000-kernel weight estimation models were diverse in different years and growth stages.The impact of the amount of nitrogen fertilizer application on fungicide efficiency against wheat powdery mildew was conducted in three years of field trials.The results indicated that reducing the application of nitrogen fertilizer could reduce of the incidence of disease and improve the control efficiency of 25%ethirimol SC.The relationship models between the 25%ethirimol SC and disease index or control efficiency,and the random coefficient regression model under different nitrogen application levels were established.There is no significant differences in the slopes of the models,but significant differences in most of the intercepts.Furthermore,the range of control efficiency of 25%ethirimol SC against wheat powdery mildew under two nitrogen application levels was obtained based on the quantile model constructed by the mixed effect model of control efficiency.The control efficiency table of the active ingredient dosages of fungicides against wheat powdery mildew under two nitrogen fertilizer application levels was calculated by using this control efficiency model.For example,if the field control efficiency reached 72%?78%,an active ingredient dosages of fungicide could be reduced by 30g/hm~2 under the reduced nitrogen fertilizer application in comparison with the regular practice.