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Problem: White Grubs; May Beetles - Phyllophaga sp. and Southern Masked Chafers -Cyclocephala imaculata

Hosts: Various turfgrasses especially bentgrass, Kentucky bluegrass, and the fine fescues.

Description: May Beetle adults vary In color from light brown to nearly black. Foliage feeding occurs at night, from April through June. Many trees and shrubs are attacked at night, but damage is usually inconsequential. The Southern Masked Chafer adult looks like a miniature form of the May Beetle but it doesn’t feed that we know of.

Females deposit eggs in grassy areas during the day. Eggs hatch into tiny grubs within 3 to 4 weeks. These grubs are C-shaped and vary from white to off-white In color. They have a brown head, 6 legs Immediately behind the head, and a dark area on the rear end.

May Beetles or 'June Bugs' require 3 years to complete their life cycle. Grubs feed for the remainder of the growing season on grass roots, then burrow below the frost line for overwintering. In the spring of the second year, the grubs tunnel up to the root zone and resume feeding; during this period the grass may be severely damaged. In the fall, they again burrow down below the frost line for overwintering. Feeding the third year stops by mid-June, when a pupal cell Is formed and the adults are produced. Adults emerge from these pupae in July and August, but do not appear above ground until April or May of the next year.

The Southern Masked Chafer has a 1 year life cycle with a slightly different occurrence of damage. Eggs are laid In July and hatch In early August. These grubs do most of their damage to turf during their peak August and September feeding periods. By mid-October the grubs have moved down Into the soil to form cells for overwintering. The grubs move up again In April to feed on grass roots, but unless numbers are very high, the additional damage seldom amounts to much. If springtime treatment Is undertaken using one of the short residual Insecticides, this application should not preclude a timely fall treatment. This grub pupates In May and emerges as adults In late June or early July.

Recommendations: Damaged turf may wilt, turn brown, and die even under conditions of minimal water stress, usually In spots or patches. Grass plants pull up with very little resistance and a section of sod can be rolled back like a carpet because the grubs have consumed the roots. C-shaped grubs are usually visible in this area if grubs are indeed the cause.

Grub-infested lawns often attract moles, skunks, and birds which feed on the grubs and may tear up the sod as they search for the insects. The grass root zone should always be inspected for grubs if dead areas appear in August or September.

A population of 3 or more grubs per square foot of turf may be enough to justify using an insecticide, particularly in dry weather. Populations of 8 to 10 grubs per square foot usually cause severe lawn damage and warrant corrective action.

In order to achieve suppression of annual white grubs (larvae of the Southern masked chafer) the insecticides should be in place while the grubs are still very tiny and are feeding in the upper 2 inches of soil surface. A critical treatment period for this species occurs about 3 to 4 weeks after the peak in adult flight and egg-laying. Unfortunately, the occurrence of these events often varies with the seasonal weather pattern. Injury becomes progressively worse during the month of August as the grubs grow in size and numbers. In most years, successful control is rarely possible unless insecticides have been applied before mid-August. In some situations, having preventive treatments in place by mid-to-late July may improve results. Early applications are more likely to be justified where thatch is very heavy (longer time required for the insecticide to reach the ‘grub zone') or in lawns with a chronic history of grub damage.

If the problem is caused by the Phyllophaga sp. grubs (3-year cycle grub commonly called either the May beetle or 'June bug') the critical treatment period is less well defined and grub age may be a more important factor. Active feeding can be expected throughout the season if Phyllophaga sp. grubs are less than 1/2 inch in length because they are probably only in the second calendar year of their life cycle. Treatment may be effective almost anytime from mid-May through September. If the majority of the 3-year grubs are an inch or more in length they are probably in the third year of larval development which means that damage should end by mid-June. If treatment becomes necessary, the insecticide should be in place well before this date for any benefit to occur.

Liquids should be applied in 15 to 20 gallons of water/1000 sq. ft. unless specified otherwise on the label. With most lawns, either a hose-end sprayer or cower sprayer (rather than a small 3-gallon compressed air sprayer) will be required to deliver the volumes of spray recommended. Prewatering @1/4 inch or more immediately before application) will aid spray penetration of the thatch barrier. Granules, however, should be applied on a dry surface. Granular applicators, preferably of the gravity spreader design rather than broadcast spreader type, are required to distribute granular insecticides uniformly. Application of either formulation should be followed by one to several irrigations, each of which applies approximately 1 inch of water (but stopping before runoff).

It may take from 2 to 4 weeks for the grubs to begin to die from the insecticide, so do not be too hasty in determining that the treatment failed. Children and pets must be prevented from entering the treated area until the post application irrigation has dried. Clean out all equipment after use and return all insecticides to areas where children can not encounter them.

A major decision that must be made is I whether the grub-damaged patched are too far gone to recover. If they are, removal of the dead and dying sections will improve control efforts. Then the insecticide should be applied to the bare soil taking care to work it into the top 2 to 3 inches with a garden rake or rotary tiller. The treated areas should not be reseeded until most of the grubs die.

References:

1. Lawn and Turf Insect Management Part I. White Grubs, K-State Research and Extension Entomology Publication 403

2. Turfgrass Insects of the United States and Canada, Cornell University Press, pg. 145-192

Last Update: 03/28/2003

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