White grub worms are damaging pests of lawn grass, ornamental plants and trees. These pests feed on the roots of host plants, causing extensive damage and reduced vigor. White grub worms are often difficult to control and most have one or two generations each year.
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White grub worms are the larval form of scarab beetles. These damaging pests hatch and pupate in the soil. Adult forms such as May or June beetles often feed on tree and ornamental plant leaves, while the larvae feed on plant roots. White grubs pose a serious threat to young forest tree seedlings grown in plant nurseries, as well as those in the forest.
White grubs do not prefer tree roots, but will attack all types of trees. Trees with heavy infestations of white grubs have symptoms similar to drought injury. During the early fall, these seedlings turn brown in color and die. Tree roots often have chewing injuries and taproots may be cut off. Some ornamental plants are susceptible to white grub injury with infested plants showing signs of reduced vigor and root injury. These pests are common pests of turf grass, causing grass wilting and browning. Turf grass is often torn up by raccoons, skunks and moles searching for white grubs to eat.
White grubs have many natural enemies such as birds and mammals that feed on them, keeping their numbers low. These pests are highly sensitive to drought, which causes them to dig deeper into the soil. Introducing bacterial milky disease has not been shown to control white grubs.
Insecticides in the form of soil drenches are often effective if applied before planting ornamental plants and trees. If grub populations are higher than one or more grubs every 2 square feet, preventative measures should be taken before planting seedlings. If young seedlings are already planted and suffering white grub damage, fast acting insecticides such as an aldrin solution should be applied to the root system of the tree or plant to prevent further damage.