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Identifying Insects

Purdue University Extension entomologist Tim Gibb inspects a leaf being devoured by a swarm of Japanese Beetles. The beetles feed on more than 300 different plant varieties, making them difficult to control. This pestiferous insect will feed on nearly all ornamental plants except evergreens, phlox, chrysanthemum, gladiolus, iris and a few other flowers. Repeated insecticide sprays are needed to protect high value plants.

Since the turfgrass you and your crew maintain is full of insects-some beneficial and some harmful-you must be able to correctly identify which is which. Below are the steps to take to identify and eliminate harmful pests, which if done properly, will lead to stronger, greener and healthier turf on your landscape.

Identification: Properly Identify the Insect

Detecting the presence of an insect is the first step in good insect control. When you find the insect, examine it closely to identify it to species.

This is a mature black cutworm. Note the dark, greasy appearance and the pebbly texture of the skin. Remember that other cutworm species may be present in the turf, such as dingy, darksided or claybacked cutworms. You should be aware of the kinds of cutworms in your area, their appearance, and life histories.

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.

There are a number of products on the market that make it easier to identify turf pests. One example is the IPM Scope(TM) from Spectrum Technologies, Inc. This product allows you to view, document and identify turf pest and disease pressures by using a small hand-held camera that captures and magnifies images or video by 40x or 140x. Coupled with a high-resolution picture gallery of turf diseases and pests, this turf monitoring package is useful for superintendents, turf managers and researchers.

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.

Yellow or brown tips on arborvitae indicate the presence of a small leafmining moth known as the arborvitae leafminer. Arborvitae leafminer caterpillars are only 1/5 inch long when full grown.They are so small that they can feed and complete their development inside the narrow arborvitae leaves. Infestations of this and many other leafminers can be controlled most effectively with a systemic insecticide.

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.

Steps in IPM:

  1. Routinely inspect or scout the turf.
  2. Determine changes in cultural practices that can increase turf health and vigor.
  3. Determine what is an acceptable threshold of pest damage.
  4. Time the pesticide application to the vulnerable stage in the insect's life history.
  5. Return to step 1. Begin inspecting.

First inspect your turf for damage or insects. 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.

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.


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October 15, 2019, 10:34 pm PDT

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