Damage: Distinguish between insect damage and turf disease
If the turf looks damaged, wilted, and water-starved, then an
insect may be involved. During root feeding, insect
species that feed on roots detach the thatch and blades from the
roots and permit the sod to peel off the soil without any root
attachment. In addition, some insects defoliate or suck the grass
blades. You must search in the blades and thatch to find these
insects. Blade defoliation damage appears as brown scars
where the blades are clipped off by the insect. Blade sucking
damage appears as brown lesions where the blade’s sap was removed by
the insect. Many times an area of turf is brown and damaged, but
damaging insects cannot be found. Search for the insects along the
margin of brown and green grass.
When turf damage is noticed and before applying pesticides, make
sure insects and not diseases or some abiotic factor are the cause
of the damage. Turf damage may be caused by fungal diseases, abiotic
conditions, and improper maintenance. See University of Minnesota
Extension Service bulletins: FO-3386,
Lawn Diseases; FS-3034,
Turf Patch Diseases; MI-0488,
The Home Lawn; FS-2364,
Watering Lawns and Other Turf; and FS-1137,
Weed Control in Lawns and Other Turf.
Scouting: Find the insect
Be sure to examine an area of turf that contains living as well
as damaged grass. The most serious insects of turf feed on living
turf and are not found in dead areas. Insects found in completely
dead patches generally are not responsible for the damage. Methods
are available for discovering insects in turf. Cutworms, sod
webworms, aphids, chinch bugs, and other blade defoliating and
blade sucking insects can be detected by the flotation method.
Use a large coffee can with both ends removed and sink it into the
turf. Mix one ounce of liquid dish washing detergent into one gallon
of water and pour the soapy water into the container. In a few
minutes, the soapy water will irritate the insect, the insect will
release its grasp, and the insect will float.
Root-feeding insects such as white grubs and billbugs will
not respond to the flotation method. Grubs feed by separating grass
blades. Billbug larvae are legless and live inside the grass sheath
and do not separate blades from roots until the last larval stage
(instar). Sample grubs and billbugs by looking for insects in grass
roots and in the soil layer beneath the roots. If infestations are
heavy, the grubs will have removed most of the grass roots and the
turf will roll back like a carpet.
Management: Use IPM principles
Integrated Pest Management (IPM) is a decision-making process
that includes scouting, damage threshold, control options, and
timing of insecticide application. IPM practices conserve beneficial
insects and promote pesticide usage at the vulnerable stage in the
pest’s life history.
- Routinely inspect or scout the turf.
- Determine changes in cultural practices that can increase turf
health and vigor.
- Determine what is an acceptable threshold of pest damage.
- Time the pesticide application to the vulnerable stage in the
insect’s life history.
- Return to step 1. Begin inspecting.
First inspect your turf for damage or insects. This is called
scouting. Look for discoloration, defoliation, and separation of
grass from roots. When investigating turf damage, pay particular
attention to whether the damage spreads.
After detecting insects, the next step is to determine if the
insects are pests, harmless, or beneficial. Only pest insects
warrant treatment. Thresholds have been established for some turf
insects. Thresholds are the maximum number of insects per specified
area that can be tolerated without obvious turf injury. Often
thresholds are general and not specific guidelines, because other
factors influence damage, such as drought, grass cultivar, and
traffic and compaction of the grass. For example, heavily fertilized
golf courses usually contain the most insects.
In Minnesota, most home lawns occasionally need chemical
management for insects. Fungi cause more damage than insects. For
those instances when insects are damaging the turf, suggested
pesticides are given at the end of this bulletin.
After locating the damaging insect, time insecticide usage to the
vulnerable stage of the pest. Insects are often more susceptible to
treatment in a certain stage in their development, often when the
immatures are actively feeding. Also, the judicious use of
conventional insecticides helps preserve beneficial insects that
naturally regulate pest insects. Applying scheduled sprays, without
determining if the insect is present, can lead to expensive
pesticide applications, create pest populations resistant to the
pesticide, and disrupt the natural control by beneficial insects in
the turf.
Note to homeowners:
A robin icon indicates the
insects described below can be found in household lawns in
Minnesota. All pests can potentially be found on golf courses and
athletic fields.
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