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June beetles and white grubsAdult May or June Beetles 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 three to four weeks. These grubs are C-shaped and vary from white to off-white in color. They have a brown head, six legs immediately behind the head, and a dark area on the rear end. May Beetles or "June Bugs" require one to three years to complete their life cycle. Grubs feed for the remainder of the growing season on grass roots, then burrow deeper into the soil 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 one-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 an adult in late June or early July. 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 three or more grubs per square foot of turf may be enough to justify using an insecticide, particularly in dry weather. Populations of eight to ten 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 two inches of soil surface. A critical treatment period for this species occurs about three to four weeks after the peak in adult flight and egg-laying. 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. Bayer Advanced Season Long Grub Control with Merit is recommended to be applied early June. 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. It may take from two to four 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. Date: 5/25/07
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