How To: Identify White Grubs

White grubs are one of the most destructive insect pests of turf. They feed on grass roots and can destroy the entire root system of the plant, killing large areas of turf in a short time. Turf-infesting grubs are the larvae of beetles in the scarab family, and correct identification of them is important to help you determine management strategies and timing of controls. Their distinctive “C”shape is familiar to most turf managers. However, with only the larval stage present, could you tell one species from another? Identifying grubs is a useful skill because control recommendations vary among species.

Mole, skunk and bird activity and dead or dying patches of turf that pull up without roots are signs that should make you suspicious of a grub infestation. The only sure way to know, however, is to cut into the turf in several locations and look for grubs in the turf root zone. Once you have obtained grub specimens, the next step is to identify the grub species.

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The best characteristic to use for grub identification is the raster pattern — the arrangement of the small hairs and spines on the raster, the ventral side of the grub's posterior end (see diagram at top right). This patterning is characteristic for most species. You can view it with a 10x eyepiece, available from many suppliers and surplus outlets.

Although numerous kinds of grubs exist, a relatively small number are responsible for most damaging infestations. Here, we show the most important species you're likely to encounter. So, with grub in hand, match the raster pattern you see to one shown here and find out which grub species is bugging your turf.

*The genus Phyllophaga includes more than 100 North American species, which are usually referred to generically as May or June beetles. Fewer than 10 of these species account for most of the damage caused by May or June beetles, and their rasters all resemble the generalized pattern shown here.

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