Egglaying begins soon after adults emerge from the ground and mate. Females leave plants in the afternoon, burrow 2 to 4 inches into the soil in a suitable area, and lay their eggs. Females lay 1 to 4 eggs every 3 to 4 days for several weeks – a total of 40 to 60 during their life. The grub or larvae stage hatches from the egg. The beetle then spends about 10 months of the year in the soil as a white grub. The grubs grow quickly and by late August are almost full-sized. Grubs feed on the roots of living plants, mainly grass. As the grubs chew off grass roots, they reduce the ability of grass to take up enough water to withstand the stresses of hot, dry weather. As a result, large dead patches 5 to 20 feet in diameter develop in the grub-infested areas. The sod on these dead patches is not well-anchored and can be rolled back like a carpet to expose the grubs. If the damage is allowed to develop to this state, it may be too late to save the turf. Early recognition of the problem can prevent this destruction.
Both Merit and Dylox are relatively safe for humans and the environment. The active ingredients in both are very low and are broken down by soil organisms. Dylox and Merit are both effective grub controls when timely and properly applied. Merit gives 98% control of grubs when applied from July 1st – August 15th. It is best to water the product in well shortly after application. Dylox has less of a residual effect and is best applied from August 15th – September 15th and watered in thoroughly. Dylox may be applied in early to mid April to kill resurfacing grubs, but since most of the grub damage is done in early fall, hitting grubs then is most effective. A good idea is to rotate these products by using one product one year and the other product the next year so that a resistant population of grubs cannot build up.
Hand collecting or bag trapping obviously is not the most effective method of control, but can be used to protect valuabe plants when beetle activity is relatively low. The presence of beetles on a plant attracts more beetles. When you remove beetles daily by hand from a plant, only about half as many are attracted to that plant compared to those on which beetles are allowed to accumulate. Another method is to use a commercial or homeade trap such as Surefire’s Japanese Beetle Trap. This bait mimics the scent of a female pheremones attracting thousands of beetles in just one day.
CONTROL WITH CHEMICAL INSECTICIDES
The following insecticides may be used to control Japanese beetles. Repeated applications may be necessary because of the relatively short residual effect of the products. Also, a significant rainfall shortly after applicaton may reduce the insecticide deposit below effective levels. Plants which grow rapidly and are especially attractive to the beetles are most difficult to protect. Roses unfold quickly and are especially attractive to beetles. When beetles are abundant, nip buds and spray to protect the leaves or cover the roses with netting to keep beetles out. Be sure the insecticide you use is registered for use on the crop you spray, especially if it is a food crop. Wait a few days after spraying to harvest.
Sevin Spray – Is effective for the control of many insects on lawns, ornamental plants, vegetables and fruits when used as directed. Apply when insects or damage appears. Spray in early morning or late evening to avoid injury to Bees and to crops from spraying during high temperature. Spray to point of run-off, monitor insect activity and repeat applications at 7 – 10 day intervals if necessary.
Eight Spray – Kills over 100 different insects. Residual control for up to 4 weeks. For use on lawns, trees, shrubs, flowers, fruits and vegetables. It has a slower kill than Sevin but the residual effect is longer.
Sevin/Eight Dust – Ready-to-use and can protect vegetables, ornamentals and lawns from insects. Can also be used on Cats and Dogs to control Fleas and Ticks. Apply the dust directly from canister onto plants. Repeat application if necessary at 7 – 10 day intervals.