Grubs
Grub damage usually appears in northern Illinois in August and early
September. This damage will appear as browning of the lawn. Consider
that this also could be due to problems such as drought, poor soil and
diseases. However, grubs are easy to find by lifting sod in damaged
areas and checking the root zone for the whitish grubs. Don’t treat
for grubs that don’t exist! Skunks and raccoons may tear up lawns
in search of grubs, even when grub numbers are relatively low. Typically
a population of about 8 to 12 grubs per square foot causes lawn damage
that requires control; whereas lower populations may not damage the
grass, they may attract skunks and raccoons.
Lawns showing damage from grubs may be treated with an insecticide.
Insecticides available for homeowners include Diazinon (25% EC [liquid]
or 5 % granular); trichlorfon (Dylox) (6.2% granular); bendiocarb (Intercept);
or imidacloprid (Merit, GrubEx) for control of white grubs. Promising
newer products (including biological controls) are being researched
and may be appearing in future recommendations.
Read all insecticide label directions, then apply to damaged areas.
Water the insecticide into the soil immediately. If treating a large
area, stop after a portion has been treated and water the material in,
then complete the rest of the lawn area needing treatment. Only treat
in and around affected areas; grubs may only be in a small part of the
lawn. Imidacloprid is suggested to be applied a few weeks prior to anticipated
grub infestations.
Spring treatment for annual white grubs is not suggested since the
grubs feed for a short period of time in spring and are reaching maturity,
thus are not controlled easily. In addition, turfgrasses are actively
growing at that time and usually don’t show damage.
Source: Bruce Spangenberg, Extension Educator, Horticulture, University
of Illinois
Mid-Summer 1998
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