Control of Japanese Beetles and White Grubs
The Japanese beetle adult and its grub damage lawns as well as certain desirable plants. Information on this page includes description of adult Japanese Beetles and their White Grub immature stage, life cycle of grubs as they migrate from shallow to deeper areas in the soil, adult beetle damage to plants, description of grub damage to lawns, cultural practices, timing of white grub control, suggestions for controlling adult Japanese Beetles that feed on leaves of plants as well as the control of White Grubs that infest lawns or grasses.
Control of adult Japanese beetles can be a concern but control of white grubs is important to maintain a healthy lawn. White grubs are the immature stages of different beetles that cause damage to plants, grasses and lawns. Japanese Beetles, May Beetles, June Beetles and Chafers are the adult insects that invade certain areas at certain times of the year. Their young or immature stages are what we call White Grubs. General description and other information can be found by going to the White Grub web page where the grubs of Japanese Beetles, June Beetles, May Beetles and chafers are discussed as a group.
Adult Japanese Beetles are quite colorful and easy to recognize once you
know their markings. This beetle can be distinguished from other damaging
beetles (June beetle, May beetle, chafers). The Japanese Beetle (adult
stage) has as shiny appearance. Its body has a metallic green color that
is in sharp contrast to its outer wings which are bronze colored. In this
adult stage the bug can cause moderate to severe damage to the desirable plants
in your landscaping.
Immature Japanese beetle grubs can be from .5 inches to 1.5 inches long, depending on the instar or stage of its development. This grub is identified by the noticeable "C Shape" of all White Grubs when it is at rest in the soil. This immature stage of the Japanese Beetle will be described in more detail in Japanese Beetle Biology as well as in white grub control.
Japanese Beetle Biology
The adult Japanese Beetle can be seen in the spring of the year as it
begins its feeding and reproductive cycle. They are most active in
daylight, as opposed to May or June beetles that are more active at night.
Adult beetles fly to certain plants where their pheromones tend to bring them
together in groups or clusters. They will be most active on days that are
sunny and warm.
Once the feeding and mating is in full swing, the mated female beetle begins to fly to the soil to lay her eggs and back to the plant material for food. With each trip to the ground, she will lay only a few eggs but the routine is repeated until she has deposited about 50 to 60 eggs. These eggs are not left to the elements but are deposited in the soil where they usually hatch in one to two weeks.
Newly emerged grubs that have just left their egg stage begin to feed on organic material near the surface of the soil. This is the stage that is easiest to control. The grubs are tiny and very close to the surface, two points of interest when applying grub control insecticides.
These grubs continue to feed until temperatures begin dropping. By late September and early October, most of these grubs begin to migrate deeper into the soil where they will hibernate for the duration of the cold winter months. At this time of year, soil applications of pesticides for grubs (or grubacides) will not be very effective and the practice is discouraged.
The grubs have gone through their first two molts by early fall.
They are in their third instar during the hibernation period. This period
is spent up to 8 inches of depth in cells where they are protected from cold
Once the Japanese Beetle grubs have finished their final active stage of development they will pupate in cells that are about two to four inches deep in your soil. After a couple of weeks in their pupal cells, newly formed adult Japanese Beetles emerge to begin the cycle all over again.
Adult Beetle Damage
When Japanese Beetles are in their feeding and mating stage, they are
often easy to recognize as they tend to cluster in areas where mating
occurs. They are also daytime flyers and prefer plants in warm, sunny
areas. The characteristic of feeding from the tops of leaves is one that
shows definite signs of damage. Small insects often feed from the bottom
side of plant material which leaves small holes from piercing/ sucking
mouthparts. Worms or caterpillars tend to feed from the edges of leaves
which shows bite marks that are easily distinguished from adult feeders.
Damage of Japanese Beetle Grubs to Lawns
White Grubs (as the immature beetle larvae are commonly named) feed on the roots of grasses and some plants. This loss of roots can be severe enough to totally separate the turf from the soil. When this happens you can actually roll up sections of the grass as if it were a strip of carpet. Other signs of white grub damage is a yellowish tinge in grass color. In some cases these areas can actually brown out. Signs of grub predators are obvious as skunks, raccoons, birds and moles feed on the protein source these creatures crave. Certain animals such as raccoons, skunks, armadillos and moles can in turn do their own damage to your lawn. Ridding your lawn of white grubs is sometimes the solution to problems with burrowing or digging wildlife.
Adult Japanese Beetle Control on Plants, Shrubs
When populations of adult beetles are too high to justify hand picking the
pests or when damage to desirable plants in your landscaping is noticeable, you
should treat the plants to bring the population down to a manageable level.
Control of Japanese Beetle White Grubs in Lawns
When control of Japanese Beetle grubs or prevention of the lawn pest is needed, cultural practices, timing of pesticide applications and type of pesticide to use must all be considered.
The irony of white grub infestations is that they usually attack lawns that are well maintained and irrigated. By nurturing a beautiful lawn and surrounding landscape we actually invite beetles and their destructive grubs. These pests are attracted to grasses that are closely cut (such as mowed lawns and cropped pastures) and to areas where the soil is constantly wet or moist. Frequent, light watering of your lawn is not as beneficial to the turf as less frequent but deeper irrigation. In other words, watering the grass for longer periods just a few days each week (the number can vary in different areas) is a better practice than watering lightly every day of the week. Good irrigation practices are not only more important in the development of a strong root system but also attracts fewer egg laying Japanese Beetles.
White grubs are easiest to kill or control when they are in their first
instar and when they are close enough to the surface to be effected by your
pesticide application. This criteria can be met by applying proper
insecticides to the area in late summer. When in doubt, contact your
local county extension office. Ask when the the egg laying of Japanese
Beetles usually occurs in your area. When using Merit
Systemic Insecticides, application can be made prior to egg laying or during
the egg laying period. Merit products (containing Imidacloprid) are
available in wettable powder concentrate (a 75% concentration) and granular
formulations. Most professionals prefer to use Merit
.5 G Systemic Insecticide Granules, the highly concentrated granular form,
when treating for Japanese beetle larvae prevention, maintenance and
control. Most over the counter or store brands of grub control granules
contain only 0.2% active ingredient instead of the 0.5% active found in Merit.
Merit Systemic Insecticides for White Grub Control
The best white grub control products on the market contain Imidacloprid. This active ingredient has been a tremendous help in white grub control, due to its long residual and systemic properties. In the past, pesticide applications had to be absolutely perfect in timing - otherwise the applications would not give a good kill of the grubs.
With Merit Systemic insecticides we can be reasonably sure of season long
control of grubs when timing and conditions are perfect. Even if timing is
not perfect you will achieve better results with Merit than with conventional
contact insecticide sprays or granules.