Prediction method for spatial distribution of corn borer based on unmanned aerial vehicle images and semivariance function

Serious pest of Asiatic corn borer in China would lead to yield reduction by more than 30%. Precise prediction and variable rate prevention of corn borer are required for cite-specific management nowadays, since too much chemical usage lowers the quality of agricultural product as well as deteriorates the pollution of agricultural environment. The farmers producing silage corn are in face of serious problem of sustainable development. Semivariance function for spatial distribution prediction is the basis of cite-specific management for corn borer. The objective of the research was to find the optimum semivariance function and prediction model for Asiatic corn borer in Shenyang. A circular area around Dayanghe Village with a radius of 2 km was selected as core experimental area. Five other villages were located around Dayanghe Village. Silage corn was planted by China Huishan Dairy Holding Company Limited in the fields among the 6 villages. Grain corn was planted in some small fields around the houses by farmers. PHANTOM 4, unmanned aerial vehicle (UAV) with the camera of FOV 9420 mm, was used to collect the high resolution image. The ground resolution was 0.04 m. The villages, corn straws, and corn fields were interpreted through the UAV images. Both percentage of pest damaged plants (91 sampling points) and percentage of overwintering worms were investigated manually in 2016. And the villages in the research area were divided into grids. The life cycles of Asiatic corn borer, the impact factors of spread, and the spatial variability of percentage of pest damaged plants were studied. Quantity of worm source and spread distance were the key impact factors of the spread behavior of corn borer. Only the larvae and adults have the spread capability, and the adults of corn borer could spread for a large area. The results showed that the spatial variability of pest damaged plants was significant, whose standard deviation was 12.03% and coefficient of variation was 47.38%. It proved that variable rate fertilization for corn borer cite-specific management was necessary. The distribution of percentage of pest damaged plants fitted log-normal distribution, whose K-SP was 0.084. Furthermore, zero-order exponential model was the optimum semivariance function for the fitting of pest damaged plants distribution by cross-validation. Correlation coefficient between overwintering insects and pest damaged plants was 0.61. Therefore, the spatial distribution maps of Asiatic corn borer could be produced through investigating the percentage of pest damaged plants and Kriging interpolation with zero-order exponential model. Only worm sources could not precisely predict the distribution and influence degree of corn borer because of numerous complex impact factors. But the investigation of overwinter worm sources was meaningful for occurrence degree for the current year. Compared with traditional spraying in the research area, the dosage of variable rate spraying reduced by 28.1%, which supposed the spraying dosage of level Ⅱ was 70% of that of level Ⅲ. Therefore, the reduction of spraying dosage was obvious, and the variable rate spraying was valuable and should be encouraged. In conclusion, the technical route of this paper by using UAV and ground investigation, can be the implementation approach for cite-specific management of Asiatic corn borer, and can reduce pesticide waste and environmental pollution. © 2017, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.