Monitoring for white grubs involves sampling several locations across an area of turf. It is important to use a uniform method to accurately assess the population. Walk in a zigzag pattern across the
field, taking samples at 10-20 foot intervals from at least 10 locations. Begin sampling in August when grubs are easily seen and actively feeding, but before signs of injury are visible.
Take square foot samples using a small shovel to cut through the turf and thatch on three sides of a square. Peel back the turf and inspect the thatch and upper 2-3 inches of soil. To find the grubs, shake the sample, and probe through the soil and roots with a pocket knife or screwdriver. Count the number and species of grubs found at each sampling site and record these on a map of the area. Replace the sod after sampling and irrigate thoroughly. A quicker method is to use a golf course cup cutter. This cuts a round core of about 1/10 square foot. Multiply the average grubs per core by 10 to get the approximate number of grubs per square foot.
White grubs are distributed in patches. Be sure to sample in the most likely turfgrass habitats. Japanese beetles and European chafers prefer grass in sunny areas, and high quality turf near the adult's favorite food plants. May/June beetles often lay large numbers of eggs under or near exterior lights. If white grubs are not detected but damage is present, examine the turf for other causes of injury such as disease, excessive thatch, moisture stress, heat damage, or other insect pests.
Japanese beetle and European chafer. Irrigated turf has a tremendous ability to recover from injury.
Even so, irrigated turf with more than 20 grubs per square foot will likely suffer from water stress. In
un-watered turf, 5-10 grubs per square foot may result in brown patches.
May/June beetle. Large grubs can cause more damage. Turf injury is likely if more than 10 grubs
per square foot are found on irrigated turf, or if more than 3-5 per square foot are found on low maintenance
Do not plant roses, grapes, or lindens around high maintenance turf areas.
White grubs usually need moist soil for eggs to hatch. The young larvae are also very susceptible
to dry conditions. In areas where turf can stand some moisture stress, do not water in July and early-
August when white grub eggs and young larvae are present. Use water management cautiously; dry
soil will accentuate any existing white grub damage.
Adult Japanese beetles are highly attracted to traps baited with floral and pheromone lures. The
traps are useful for monitoring the presence of adult populations, but they are not useful for controlling
turf damage. Traps may have some utility for managing Japanese beetles on ornamentals, although
plants near traps can sustain increased damage. These traps are recommended only as a means of
drawing beetles far away from very susceptible landscape plants. Place them as far away as possible
from valued ornamentals and high-maintenance turf.
Certain nematodes (microscopic wormlike animals that can cause disease in insects) have shown
some promise for controlling white grubs in turf. Steinernema glaseri works consistently but may be
difficult to find; Heterorhabditis bacteriophora and H. heliothidis provide moderate white grub control.
Other species, including S. riobravis, H. megidis, and H. zealandica have provided good white
grub control in research trials.
Nematodes are very sensitive to drying and must be used carefully. They should be watered in as
soon as they are applied to turf, either by applying them during rain, or by irrigating immediately after
application. Do not apply nematodes during the hottest parts of the day. When preparing them for use,
keep them cool and out of the sun; store them in a cooler if the day is hot. An excellent resource on the use
of nematodes for grub management is: www.oardc.ohio-state.edu/nematodes.
The naturally occurring soil fungus Beauveria bassiana is commercially available and may be
effective against white grubs. B. bassiana requires high humidity to infect insects. Research has shown
promising results, but only when the fungus is used during a wet summer.
White grubs are most susceptible to chemical control when they are very small. The degree of
control is highly variable from site to site and year to year, but insecticides may provide 50-80%
control of white grubs. If irrigation is available, liquid insecticide applications can be effective if
applied with proper timing (usually late summer). Granular insecticides are often more effective
where irrigation is not possible.
Apply spot treatments in late August and early September. Early morning or evening is the preferred
time for insecticide treatments. If soil moisture is unusually low at the time of application,
consider irrigating the area a day or two before the intended application to draw the grubs up into the
upper root zone. Irrigate after application to wash the treatment into the soil. Three weeks after
treatment, evaluate the treatment by sampling for grubs where the original samples were taken. Be
sure to record the results for future reference. Keep in mind that no insecticide will eliminate an entire
grub population, but the numbers can be reduced below the action threshold.
Research indicates that most of the pesticide applied for grub control ends up in the thatch. Irrigating
before or after an application does affect this binding. If the thatch layer is an inch thick or
more, grubs probably will not contact an effective dose of any applied insecticide.
Anyone making pesticide applications on school property must
be licensed by the Board of Pesticides Control. See “Standards
for Pesticide Applications and Public Notifications”.