A healthy, well-tended lawn is a beautiful thing, but like any planting, it can experience a variety of problems. Chewing insects, like grasshoppers, may attack grass blades, and burrowing critters, like gophers, may munch through grass roots and cause green tops to die. It’s not too difficult to spot dying patches of lawn. It is often a challenge, though, to detect what is causing the problem and how to treat it. Learn about common lawn pests and the symptoms they cause, along with some tips on treating the problem.
When moles are at work, you’ll see volcano-like mounds of soil and raised ridges (feeding tunnels) running through turf. The soil mounds are the spots where moles push to the surface all the soil they’re excavating from the deeper tunnels you can’t see. Moles tunnel through lawns feasting on insects, worms and grubs. They’re more common in overwatered lawns, because damp soil is easier to dig. Traps work but definitely have a high ick factor. Castor oil is effective in encouraging moles to move on. Use liquid or granular formulations.
As snow melts in spring, it’s not uncommon to spot this type of lawn damage. These aren’t the lawn equivalent of crop circles; they’re pathways created by voles, which are small rodents. These critters chew their way through grass and then literally beat a path through those areas. Hidden beneath snow, voles roam freely across lawns in open areas. After snow melts, they retreat to brush and long grass, cover that hides them from predators like hawks and cats. Fill in vole trails with quality potting soil or compost. Grass should mend itself. Before snow arrives, treat areas prone to vole activity with castor oil to help repel these munchers.
When it comes to identifying what’s chomping your lawn, much of the time you have to rely on clues. With Japanese beetles, for instance, you may see beetles physically on the lawn. Most likely they’re laying eggs in the soil and not really feasting on turf. But if you see Japanese beetle or June beetle adults elsewhere in your garden (maybe feeding on roses or raspberries) and later see places in your lawn that are dying, chances are you’re dealing with lawn grubs.
Lawn grubs are the larval form of Japanese, June and a few other beetles. Which beetle grub your lawn is most likely to be infested with depends on where you live. Grubs are a big problem in the Northeast, Midwest and Southwest, where irrigated turf provides a grub oasis in the otherwise desert country. Grubs make their presence known by creating patches of dying lawn as they devour grass roots. Sometimes you’ll also notice places where the lawn has been burrowed as hungry skunks or armadillos dig for grubs. Treatments for grubs include milky spore, granular pest control products and nematodes.
Signs of digging or adult beetles provide easy-to-discern clues about what’s attacking a lawn. But when an insect is hiding in grass crowns or working underground, it’s tough to spot the villains. Pouring soapy water on a patch of lawn (called a drench test) provides an easy way to flush pests to the surface. Dissolve two tablespoons of dish washing detergent (lemony scents work best) in two gallons of water. Pour the solution over a square-yard area of lawn. Observe carefully. You may spot mole crickets, chinch bugs, cutworms or armyworms scrambling up from soil and grass to escape the suffocating soap.
Another test you can use to flush out lawn-damaging critters is the floatation test. Start by removing the top and bottom of a can, like a paint can or large (No. 10) food can. Find an area where problem lawn borders healthy lawn, and push the can into soil 2-to-3 inches deep. Fill the can with water, and watch for insects floating on the surface. This is an excellent test for cinch bugs. With both of these tests, count the number of insects you observe. Check with a local garden center or extension office to learn threshold numbers (how many insects equal a problem).
Chinch bugs tend to attack lawn in sunny areas, sucking the juices from individual grass plants and injecting toxins that loosen grass from soil. These insects are tiny, only 1/20 of an inch, and have black bodies with shiny white wings. Chinch bugs tend to dwell in the thatch layer or in the crowns of individual grass plants. You can see them with the naked eye on a lawn if you get down to grass level, but using a drench or floatation test works better. Dethatch your lawn when needed to reduce hiding places for these insects. Treatment options typically focus on insecticide applications, although insecticidal soap works well, too.
Mole crickets are one of the most devastating lawn pests throughout the Southeast. These insects tunnel through soil, and different species affect different parts of the country. As they burrow through soil, mole crickets feast on insects and decaying plant matter, along with grass roots and shoots. A lawn infested with mole crickets has irregularly-shaped brown patches and feels spongy when you walk on it. Finger-width tunnels and dying grass that lacks roots are key clues that mole crickets are at work. Use a drench test to be sure. Treatment options typically focus on insecticide applications. Mole crickets prefer moist soil for digging. Make sure you’re not overwatering your lawn.
European Crane Fly
The European crane fly is primarily a pest in the Northwest section of the country. Adult insects resemble an oversized mosquito and often perch on lawns or the flat walls of a home. Larvae, called leatherjackets, hatch in fall and feed on grass roots through the region’s mild winter. The damage they do appears in spring. When lawns should be greening and growing rapidly, they seem to stall and become weaker. Inspect the top 3 inches of sod for leatherjackets from February to mid-May. The best places to check are where the grass is in poor shape, yellowing or even missing. Shady and wet areas are another place to check. Count how many larvae you find. Compare that number with the treatment guidelines created by turf and entomology experts at Oregon State University and Washington State University (available online or through your local extension office).
When selecting a treatment for lawn pests, it’s tempting to search for a silver bullet pesticide to deal with the problem. Remember that the best defense against any pest is maintaining a healthy lawn. Aerate, dethatch, fertilize, mow and water on a schedule that favors healthy turf growth. When it’s time to treat for pests, consider options beyond insecticides, like nematodes or milky spore bacteria. Some pests respond to drying out an overwatered lawn. Others die when you apply fertilizer properly to spur healthy grass growth. When applying any chemical, follow label instructions carefully. Many insecticides need watered in after application to move the chemical into soil where the pests live.