Johnsons's Garden Centers Text File document - copyright 2002
PDF file available at http://www.johnsonsgarden.com/newsletter/lawncare.html

Get Ready for Grubworms
June 2002
Alisa DePontier, Johnson's East Store

    If you've ever had grub damage on your lawn, you know the importance
of treating before the grubs start munching on the grass roots. Grubs
can do a lot of damage very quickly.

    To check for grubworms, take a garden shovel and "scalp" a patch of
grass from the soil. Go deep enough so that you don't disturb the roots
too much. Often, when the grub damage is severe, you can actually lift
the sod like tugging on a carpet.

    Controlling grubworms can be a little confusing because there is
actually more than one type of grub found in our soil. The "bad guy," or
the one who wreaks so much havoc on our lawns in the fall, is the
Southern Masked Chafer (or annual grub). This grub has a one-year life
cycle and the adult looks like a miniature form of the "June Bug" (which
does not feed on anything).

    Southern Masked Chafer eggs are laid in July and hatch in early
August. These grubs do most of their damage to the turf during their
peak August to September feeding periods. By mid-October as the soil
temperature cools the grubs stop feeding and move down deeper into the
soil where they over winter below the frost line.

    When the soil warms up the following spring, the grubs move up to
the grass root zone where they do minimal feeding (if necessary to
complete their development). Mature grubs form an earthen cell from
which the Southern Masked Chafer beetle emerges approximately three
weeks later to mate and repeat their yearly cycle.

    The presence of Southern Masked Chafer grubs in lawns may go
unnoticed until late summer or early fall. There may be the appearance
of an off-color spot in the lawn. Damaged turf may wilt, turn brown and
even die, usually in spots and patches. Affected grass looks very much
like drought or brown patch.

    A population of three or more grubs per square foot may be enough to
justify the use of an insecticide under hot, dry weather conditions.
Populations of 8-19 grubs per square foot usually cause severe damage
and warrant corrective action.

    There are two types of grubworm treatments. You can either apply a
preventive such as Merit or you can apply a curative treatment with
Diazinon or Dylox.

    Think of Merit as insurance against grubs. Merit is a stomach poison
that is taken into the root system of the turf and stored there. As the
newly hatched grubs begin to feed they are killed. Merit must be applied
several weeks (30 days) prior to when the Southern Masked Chafer hatches
to allow adequate time for the uptake of the product into the plant. The
best time to apply Merit is in late June to early July.

    Diazinon and Dylox are "contact" insecticides. In order to achieve
good control of Southern Masked Chafer grubs the insecticide should be
applied while the grubs are still very tiny and feeding in the upper 2"
of the soil. Late July through mid-August applications give the best
control. Early application is even more critical when there is a layer
of thatch that the insecticide must penetrate to get to the grub zone. A
deep watering several days prior to application of Diazinon or Dylox
will bring the grubs closer to the soil surface.

    It may take from 2-4 weeks for the grubs to begin to die from the
insecticide so it's best to treat before you start to see the damage.
Otherwise the grubs will continue to feed on your lawn while the product
takes effect.

    All grub treatments including Merit, Diazinon and Dylox must be
followed by several deep waterings of at least 1/2" each.