Damage From the Scarab Beetle Grub at a Vegetable Garden

Tagged As:

Occasionally during garden chores, a C-shaped white grub is going to appear in the soil. These somewhat shiny, lotion- to white-colored insects have brownish heads and legs, with the end of the abdomen somewhat grayish. They’re immature forms of various scarab beetles, one of the largest families of beetles. They feed on decomposing organic matter and also on roots of plants. Based on the type of beetle grub it’s, it might be feeding on decaying wood, manure or compost instead of damaging plant roots. It is hard to tell what sort of beetle grub it’s unless you’re an expert.

Grass Root Feeders

Many scarab beetle grubs that feed on roots eat grass roots. If grass is growing as a garden weed, or if there is nearby turf, it is likely that the grubs are feeding that rather than your garden plants. The scarab beetles that prefer grass roots are primarily masked chafers (Cyclocephala spp.) and May and June beetles (Phyllophaga spp.) . Adult masked chafers are golden brown with darker brown heads and hairy undersides. May and June beetles are somewhat lustrous brown to dark brown beetles that fly to lights at night.

Tree Root Feeders

Some scarab beetle grubs prefer tree roots. If trees such as almond (Prunus dulcis) develop close enough to your garden so that their origins extend into garden soil, scarab beetle grubs of this tenlined June beetle (Polyphylla spp.) May be feeding on the tree roots. Adult beetles are light brown with longitudinal cream-colored stripes down their backs. Other species of lined June beetles feed on roots of vegetables, harvest plants, garden fruit trees and conifers. Based on the sort of lined June beetle, grubs could be damaging origins of plants. Based on the variety, almonds are hardy growing in U.S. Department of Agriculture plant hardiness zones 5 through 8.

Compost Feeders

A large beetle with metallic green head and undersides and light brown wing covers, the green fruit beetle (Cotinis mutabilis) is often seen in summer as it flies about looking for ripe fruit to eat and places to lay its eggs. It’s a clumsy, loud flight. All these beetle grubs are larger than root feeders, and you’ll find them most often in compost stacks and accumulations of rotting debris. They’re considered beneficial in compost stacks because they aid in breaking down the organic material. Should they occur in vegetable gardens, then they may be feeding on decomposing organic matter rather than live origins. But they may eat origins if compost isn’t available to them.

Management Practices

Although locating some white grubs in the vegetable garden can be alarming, even if they are not plentiful, the best practice is to remove them as you locate them at the soil. Put them in a sealed container and discard them. Do not use plastic bags since they can chew their way out. To manage residents of the green fruit beetle, screen compost until you add it into your garden and remove and destroy the grubs. Remove accumulations of compost, manure or leaf piles that harbor the grubs. Pesticides shouldn’t be used unless the pest has been identified and is present in damaging numbers. The University of Arizona Extension notes that in case you keep poultry in your lawn, they’ll scrape and consume all of the white grubs they discover.

See related