Burrowing Grubs in a Southern California Garden

Most beetle species have larval periods where they feed vigorously on organic material until they pupate into their adult form; grubs are larvae beetles. In Southern California, several grub species feed in particular gardens, from chafers (Cyclocephala spp.) to June beetles (Cotinis mutabilis). Each grub species prefers different garden areas for sustenance, such as lawns or tilled flowerbeds.

Masked chafer larvae specific to Southern California are cyclocephala hirta and cyclocephala pasadenae. Both beetles begin as tiny, white larvae hidden in turf grass; adult beetles lay their eggs deep in grass blades for protection. As the larvae become active, they burrow into the soil to reach densely packed grass roots. Root material provides instant nourishment for growing grubs. Although most healthy lawns sustain some grub damage each year, large larvae populations cause widespread turf damage. Brown, dead spots appear across your turf. With large infestations, you can actually pull on your turf and it rises easily from the soil.

June beetle larvae prefer vegetable or flower gardens as their main food source. Instead of targeting root systems, they burrow in soil for decomposing vegetation. Garden debris, manure and compost attract adult June beetles to hide their eggs initially. As grubs emerge, they quickly dig into cultivated soil to feed uninterrupted; they are often difficult to find unless you turn the soil. You may see plant growth stunting or toppled seedlings with high, June beetle larvae populations in your garden. In fact, they attack root vegetables as well if organic material becomes scarce.

If you suspect a grub infestation, gently pull up on your turf or shallowly turn your garden soil. Approximately five grubs in a square-foot space calls for chemical intervention; grubs quickly decimate your garden with this high-density population. For masked chafers, you must water an insecticide into the soil to bring the chemicals near the larvae hidden at the root level. Follow all insecticide instructions to avoid plant or personal injury. June beetle larvae, on the other hand, tend to climb out of the soil if you apply insecticides. Do not water these chemicals into the soil, but allow them to remain on the soil surface as larvae emerge. Careful insecticide application allows you to preserve your plants from continual grub damage.

Remove a small grub infestation through turf aeration. Using a solid spike machine, you pierce the ground to create beneficial air pockets while decimating feeding larvae. For cultivated gardens, expose grubs to the air and local predators by carefully tilling the soil with a garden hoe. If you have a garden area not in use, simply overwater the area to flush larvae out of the soil; they quickly drown in wet conditions.