Determination of economic injury due to Japanese beetle, Popillia japonica Newman, feeding on corn roots
Abstract
Greenhouse and field studies conducted from 1995 through 1997 were designed to determine how root feeding by the larval stage of the Japanese beetle, Popillia japonica, affected plant growth and grain yield of corn, Zea mays. In greenhouse studies, four densities of white grubs were applied to individual potted plants and differences in plant development, extended leaf height, leaf area, dry root weight, and dry plant weight were compared. Grub feeding had a limited effect on seedling emergence with only 2% of the seedings failing to emerge due to grub injury. Differences between growth variable measurements varied from year to year but as few as 3 grubs per plant significantly reduced plant growth when compared with uninfested plants. Field studies were designed to compare the effects of grub feeding at four densities on corn plants from germination through maturity. Effects on plant stage, extended leaf height, leaf area, dry root weight, and dry plant weight were compared at three sampling dates and grain yields were recorded at harvest. Significant relationships between number of white grubs and growth variables were detected only during times of additional environmental stress on the plants. In 1995 and 1996, significant grain reduction began between 7 and 15 grubs infested per plant. This significant grain reduction was detected between 7 and 11 grubs per plant in 1997. High average grub mortality occurring at the 7 and 11 grub densities (52%) may reduce the number of grubs actually causing significant yield losses to between 3 and 5 grubs per plant. The slope of the regression equation of grain yield on number of grubs recovered per plant was used to determine the amount of grain loss per plant per grub each year. The 3-yr average grain loss was 262.45 kg/hectare at one grub per plant and 64,220 plants per hectare. The economic injury level depending on specific insecticide and grain prices was estimated to be between 9.7 and 17.2 grubs per m$\sp2$ or between 1.5 and 2.7 grubs per plant.
Degree
Ph.D.
Advisors
Gibb, Purdue University.
Subject Area
Entomology|Plant pathology|Agricultural economics|Agronomy|Ecology
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.