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There are several
species of insects that live part of their lives as grubs but the ones
that cause devastation to the lawn belong to the European chafer. This
pest has moved in from the east over the past several years and is now
firmly established.
The
European chafer has a one year life cycle. The eggs hatch in the soil in
late July to early August and the grubs begin to feed on the roots of
grass. They feed through the fall and actually do most of their damage
during this time of year. When the weather gets cold, they dig deep into
the ground for the winter. In the spring when the
soils warm, they dig
back toward the surface to feed
 some more. In late June, they turn into a
brown beetle that emerges from the ground at sundown. Masses of the
beetles swarm in trees, mate and return to the ground to lay their eggs.
If they land in your lawn, you will have grubs again.
It takes a lot of grubs to kill your lawn. Research
shows that 5 or more grubs per square foot on the average lawn is enough
to cause death to the turf. On irrigated lawns, it may take 20 or more per
square foot to do the job. That is why one alternative for managing a grub
problem is to keep the lawn well-watered throughout the season. This will
help the plants survive with a smaller root system caused by the grubs.
 Fall
is the best time to treat for grubs. They are still small and all of them
are near the soil surface until cold weather. Chemicals used for control
can easily penetrate to that depth and kill them.
Spring is a more difficult time to get control. The
grubs come to the surface as the soil warms and this may vary considerably
throughout a single landscape. Some areas warm faster than others in the
spring due to soil type and exposure to the sun.
So, it is important to wait to apply
insecticides until
the grubs are present. Dig down a few inches in several spots in the lawn
and see if you find grubs. Wait until you find several with each shovel of
soil.
If patches of grass are already dead or if clumps can be
raked up without any resistance, it needs to be replaced. A good approach
is to rake up all the dead stuff and then work up the soil. Prepare the
seedbed properly and make sure that it is graded to remove any
irregularities. It is very difficult to remove those bumps and valleys
after the grass is established.
Do a final grading, plant the seed and gently tamp it
into the ground. If you have a roller, run it over the ground but do not
put water in it. You only need a light compaction to be sure the seed is
in contact with the soil.
If during the soil preparation, you have been finding a
lot of grubs, finish the job by spreading a soil insecticide labeled for
use with grubs. These are available at places that sell garden supplies.
By using it at the end of the process, you avoid having
to dig and work soil that has already been treated with the pesticide.
Plus, in the process of watering your newly seeded area, you will be
helping the insecticide to move down into the soil to where the grubs are
located.
Regardless of what you do this spring, you need to check
for grubs again next fall. About Labor Day, take a shovel and turn over
some sod in a few places in the yard. If you find 5 or more grubs per
square foot, you need to treat again. If you do a good job of grub control
in the fall, you should not have to think about them again until the
following fall.
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