By Monte Hampton.
Ford County Extension Agriculture Agent.
I recently attended a corn and milo demonstration plot meeting, where it was brought to our attention that some type of insects were tunneling into the crown region of some of the sorghum plants.
After consulting with Phil Sloderbeck, K-State Southwest area entomologist, the pest has been identified as a sugarcane rootstock weevil (Anacentrinus deplanatus).
The weevil tends to infest sorghum sporadically, especially during dry years across the southwestern United States.
The adult weevil tends to be dark brown or black and approximately three-eighths inch long and one-eighth inch wide. The larva is a white legless grub, with amber-colored head and is about one-fifth of an inch long, when full-grown. The pupa is white until shortly before emergence, when it takes on a brownish tint. Eggs are a creamy white and oval in shape. The female weevils use their mouthparts to make a small puncture in the plant, in which the egg is deposited and concealed in the plant. About 16 eggs are laid and hatch in six days. Larvae and pupae develop in 25 and 10 days, respectively. A generation is completed in about 41 days.
Adult weevils feed on young sorghum plants and crowns. This damage is noticeable, but not as serious as that caused by larvae. Larvae tunnel into the sorghum stalk just below or above the surface of the soil. Tunnels resemble those made by other borers, except they are much smaller and do not extend up the stalk. Larvae often are found at nodes and near the outer surfaces of the stalk. Their feeding often is responsible for a drought-stressed appearance and lodging of sorghum plants. Exit holes and feeding tunnels provide favorable areas where such pathogens as charcoal rot can enter the plant.
Historically, controlling this insect has not been required. Good cultural practices that promote early vigorous plant development are beneficial against this insect. Currently, there is no effective insecticide and application techniques available along with economic threshold establishments.
For more on this pest, contact the county Extension agent.