White Grubs , Coping With Them

There are several kinds of grubs in the US that cause damage in turf and gardens.

In the South, larvae of various June beetles present a serious problem to turf. All of these grubs are soil-inhabiting species that feed on the roots of turfgrasses and other plants.

Japanese Beetle.

Adult beetles usually appear on the foliage of trees and shrubs in June and early July. The beetles are mid-day fliers, and feed on foliage for several days then dig into the soil and deposit eggs. They emerge and feed a few days then repeat the cycle. The adult Japanese beetle lives about 30 days and deposits around 50 eggs. The eggs hatch in about 10 days and begin feeding immediately. They grow rapidly and feed throughout the summer. They burrow deeper into the soil at the stert of cooler weather. In March and April they come back to the surface and begin eating again. The grub transforms into an adult beetle in June and early July. The life cycle is one year

The best time to control grubs is August in the early larval stage.By then most of the larvae have hatched. Insecticide will not control eggs. Mature larve are harder to control. Thorough watering helps move the larvae closer to the surface.

Keep in mind, also, that to be effective, the chemical must reach the soil level where grubs feed. A heavy thatch can prevent insecticides from reaching the target. Some chemicals must reach the pest immediately. Those that don't stay in the soil and are not safe in a garden. Dethatching prior to applications helps but drenching the insecticide into the turf immediately after application is needed to move the material to the soil level where the target pest is feeding. Most insecticides require watering in, especially in turf.

Grubs of the Japanese beetle can also be controlled with a dust containing spores of milky disease, Bacillus popilliae. The dust should be applied by treating spots at 5-foot spacings with 1 teaspoon of material. The dust should not be used in combination with insecticides. The disease organism requires several years to infect existing grubs in order to spread the bacteria population adequate for effective control. Thus, milky spore disease does not provide an immediate control method for a grub problem.

Another parasite, a nematode, that attacks the larvae of the Japanese beetle has been found in the Northeast. The parasite is being studied as another possible biological control of the Japanese beetle larvae.

Masked Chafers.

The northern masked chafer is found from Connecticut to Alabama and west to California. The southern masked chafer is found throughout the southwest and in Texas, Oklahoma, Iowa and Illinois.

Their life cycle is much the same as the Japanese beetle Information relative to chemical control of Japanese beetle larvae also applies to control of the masked chafer. Again, the optimal period for control of the grub with short-residual insecticides would be late July and August.

June Beetles.

Numerous species of May or June beetles are found in the South and Midwest. One species, Phyllophaga crinita, has caused extensive damage to turfgrasses in Texas and neighboring states. The adults are about 5/8 inch long and light brown with a reddish tinge just behind the head. The adults emerge from the soil in May or June, usually after a period of significant rainfall. At least two flights of the June beetles are observed each year. During these flight periods large numbers of adults can be seen flying around street lights at night.

The females lay 30 to 40 eggs at soil depths of 2 to 5-inches. The eggs hatch in about 3 weeks and the larvae begin feeding on grass roots. The insect passes through three larval stages. The third stage is the mature white grub that causes extensive damage feeding on grass roots in the fall and early spring. The larval stage of the insect is when they are most susceptible to control with insecticides. Insecticide treatments for white grub control should be made 4 to 6 weeks after the major flight of the June beetle is observed.

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