June Bugs Now and White Grubs Later

           Cary Sims

Angelina County Extension Agent

(This article appeared in Lufkin Daily News, Sunday, April 15, 2007)

It is the time of year for the June bugs, those brown bugs that congregate around light sources at night and feed on the leaves of some trees and shrubs while we are asleep.  I've had several calls about them and suggested a number of common insecticides that can do the job, but the real problem is their immature stage known as white grubs.

White grubs are the larval stage of insects commonly known as May or June beetles (or June bugs).  Texas has almost 100 species of these beetles, most of which do not cause significant economic damage to crops or horticultural plantings.  A few species, however, commonly damage turf grass and other cultivated plants.

White grubs, sometimes referred to as grub worms, injure turf by feeding on the roots and other underground plant parts.  Damaged areas within lawns lose vigor and turn brown.  Severely damaged turf can be lifted by hand or rolled up from the ground like a carpet.

The June beetle emerges from the soil and flies at night, usually after a significant rainfall or irrigation.  Flight periods may last for several weeks, during which time mating and egg-laying occur.  During flights, large numbers of adult beetles, primarily males, may be attracted to lighted windows or other lights at night.  Females, being less active fliers, are less common around lighted areas.  For this reason, turning off outdoor lights during adult flight periods may not substantially reduce subsequent grub damage.  After mating, female beetles dig two to five inches into the soil to lay eggs.  Each female can lay up to 30 to 40 eggs, which hatch in approximately two weeks.

Some Texas lawn never suffer white grub damage while others are damaged year after year.  If your lawn consistently dies out in patches during late summer and if you can verify that white grubs are the culprits, you may benefit from a preventative program.

To confirm whether you need to treat for grubs, examine several soil sections at least 3-4 inches across and four inches deep.  Sample sandy soils to greater depths.  Finding more than five white grubs per square foot justifies treatment, although some lawns with even higher number may show no damage.

Several non-chemical treatments are available for white grubs.  Beneficial nematodes within the genera Steinernema and Heterorhabditis are tiny worms that attack white grubs and other soil inhabiting insects. 

Proper timing and chemical application are critical to suppressing white grubs.  New white grub insecticides are more persistent and less toxic to beneficial arthropods and earthworms. However, these treatments must be applied early enough to kill the smaller (less that 1/2 inch long) larvae.

The insecticides imidacloprid and halofenozide are used most today for white grub control.  Imidacloprid is most effective against small and medium sized grubs but may kill some grubs larger than 1/2 inch long.  Ideally, both products should be applied within six weeks of egg-laying.  Where grub damage is already evident in lawns, and larger grubs are present, use products containing trichlorfon or carbaryl.

Post-treatment irrigation is essential for all grub control products.

(Photo: Texas Agricultural Experiment Station; photo by Dr. Milt Engelke)