University of Vermont
Department of Plant and Soil Science

Summer News Article
line

LAWNS: THE PEST PARADE

Dr. Leonard Perry, Horticulture Professor
University of Vermont

If you maintain a lawn, you may encounter several key pests during the summer.  Knowing which pests you have from the symptoms they cause, how to control them, and even if control is needed, will ensure you keep a healthy lawn with no negative environmental impact.   
   
In his book, The Lawn Bible, author (and Fenway Park master groundskeeper) David Mellor makes the important point that lawns are teeming with insects, most either beneficial (eating the bad insects, nature’s “pest patrol” as he puts it), or causing no harm.  The few bad insects get all the attention and, by trying to control all insects, you may be killing helpful ones and many innocent bystanders.  The bottom line:  you don’t want an insect-free lawn.
   
There are specific types of damage—symptoms—to watch for from the undesirable lawn pests, each narrowing down your choice of culprit.  Underground insects destroy the roots, so the plant dies from being unable to take up water and nutrients.  Other insects feed on the “crown” of grass plants—the part at the soil surface from which the grass leaf blades arise.  Others either chew leaves and stems or, in the case of chinch bugs, suck the nutrients out of the grass blades.  Other pests such as skunks and raccoons dig up lawns in search of underground insects.
   
Since several lawn problems masquerade as those from pests, but are from culture, you’ll need to get right up close and inspect your grass on hands and knees for pests.  Grass injured from drought or diseases may, at first, appear to be from insects.  A dull mower blade may tear and brown grass blades, appearing as if chewed by insects.
   
Since pests feed on live grass, any insects you find in dead patches likely are not to blame.  Look on grass blades, at the plant crowns, and in the thatch layer (the layer of organic dead and living plant parts at the soil surface) for lots of the same pest.  Get a spade and gently lift a section of turf to see if any are feeding below ground.  If the turf pulls up in your hand without any help from a spade, you likely have a grub problem. 
   
Once you’ve determined you have lawn pests, you need to identify them.  There are many online resources for such, or check with your local full-service garden center, Extension master gardener helpline (www.ahs.org/gardening-resources/master-gardeners), or plant diagnostic clinic (www.nepdn.org/home). 
   
Just because you have a known pest still doesn’t mean you must control it.  Just a few munching on your grass won’t cause much problem and you can coexist with them.  Consider options to deter pests from feeding, and least toxic products. 
   
Chemical controls are abundant, often seen advertised, and can be quite toxic as well to beneficial insects, wildlife such as pollinators and fish, your pets, and even your family.  Common ones you’ll see include the ingredient diazinon for chinch bugs, cutworms, billbugs, white grubs, and sod webworms.  Other products may contain the toxic ingredient carbaryl for white grubs and billbugs. Usually found in the product Sevin, carbaryl is one of the most widely used pesticides and is one of the most toxic to bees.  For any controls, chemical or otherwise, make sure to read and follow label directions to ensure their safe and effective use.
   
Biodegradable, and nontoxic to humans, are insecticidal soaps.  These come from salts of fatty acids, and are used on soft-bodied pests such as white grubs, chinch bugs, billbugs, and sod webworms. 
   
Increasingly popular are botanical insecticides made from plant materials.  They break down quickly, so must come into contact with the pest soon, and are not very effective on underground pests.  Pyrethrin products derive from the chrysanthemum plant, and should be used carefully as they kill beneficial insects too, as well as fish. 
   
Biological controls are those that use one organism to fight another.  Since they are living, make sure to follow the label on their storage and use so they don’t die.  Beneficial nematodes are microorganisms that attack larvae of such soil pests as white grubs (Japanese beetles), cutworms, and sod webworms.  “Bt” is the common name for a bacterium that kills some of these same soil pests.  Endophytic fungi are actually beneficial diseases that live within the grass plant, producing natural compounds toxic to pests and deterring those that chew.  You can buy some grass seeds already inoculated with them; look for the word “endophyte” on labels.
   
The key pests your lawn may encounter are those already mentioned above under controls.  White grubs are the larvae stage of any of several beetles that live in the soil.  They’ve been described as small C-shaped white croissants with legs, and brown or yellow heads.  They cause irregular shaped dead patches of turf, usually in late spring or early fall, which easily peel up like a rug.  Digging for these by skunks is another sign you have them.
   
You need to treat for white grubs when you find six or more grubs per square foot of soil.  Use a spade to gently lift a square foot section of turf.  Stir around the exposed soil to a depth of two inches, and count the grubs you find. 
   
Mature sod webworms are grayish caterpillars, about 3/4-inch long when mature.  You’ll probably see the moths first, which lay the eggs, flying up as you mow.  These larvae live in silky webbed tunnels (hence the name) in thatch by day, and feed by night.  If you have small, up to two-inch, patches of dead grass, the blades chewed off just above the thatch layer, you should see these by flashlight feeding at night. 
   
Treat sod webworms if you have more than 15 per square foot.  To find out, flush them out, literally.  Mix two tablespoons of dish detergent (lemon-scented is best) with a gallon of water and saturate a two-foot square area of lawn.  In about five minutes, count how many webworms have come to the surface. 
   
Adult billbugs are small weevils—a type of beetle—about 1/8-inch long.  They are elongated, black, and have long snouts.  The larvae or grubs in soil, which cause the damage, are white, legless, and have orange-brown heads.  They cause circular dead spots where grass stems lift easily away from the crowns.  Do a “tug test”.  Pull on dead grass stems, and if they easily break off at the crown, this is a good clue to billbugs and not sod webworms.  Look in the crown and around roots for debris resembling sawdust—another billbug clue.  Check the soil as you would for white grubs, and treat if more than one larva per square foot.
   
Adult chinch bugs are small, only about 1/5-inch long, with black bodies and white wings.  They have a distinctive triangular-shaped mark on each wing.  They produce large, circular, yellow to brown patches of turf from sucking the juices out of plant parts.  To see if you have these, and sufficient numbers to treat, get a bottomless coffee can.  Push it two inches into the soil at the edge of an affected area, and fill the can with warm water.  Any chinch bugs will float to the surface in 10 minutes or so.  Do this on the edge of several affected areas.  If, on average, you figure you have 15 to 20 chinch bugs per square foot, it’s time to treat.
   
Cutworms are moth larvae that curl up into a tight circle when disturbed.  They’re plump, up to two-inches long, and either brown, black, or gray.  They cut the grass blades off at soil level, hence their name.  Usually it takes many to damage a lawn.  Use the dish detergent test to bring them to the surface and, if you count more than 10 larvae per square foot, it’s control time.
  
 More on these pests, others, lawn diseases, and culture for a healthy lawn, can be found in the book by David Mellor.  A healthy lawn will better resist pests, and recover more quickly.


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