by Annie Deutsch, Door County UW-Extension Agriculture Agent
Earlier this summer, many homeowners around the city of Sturgeon Bay noticed extensive damage to their lawn. Due to grub feeding, some yards were reduced to patches of dirt and dead grass; damage which was worsened by skunks and other animals scavenging for the grubs.
While Japanese beetle or June beetle grubs can cause similar damage, these are not the same. The culprit: a new invasive species, the European chafer.
European chafer is a small tan to brown beetle around ½-inch long. The immature stage, or grub/larva, lives in the soil and eats grass roots. Grubs are C-shaped, white, and can get up to one-inch long (June beetle grubs are larger).
European chafer overwinters as a mature larva. In the spring they feed on grass roots, causing the damage we saw earlier this year. By late May/early June, the grubs move deeper into the soil profile and pupate, emerging a few weeks later as adult beetles. The adult beetles are active especially at night as they mate and lay eggs in the turf. Those eggs hatch, and the larvae begin to feed. They will continue feeding until there is a hard frost. As they grow throughout the fall the damage will become more apparent.
Excavations in turf this week revealed that the grubs are abundant and are medium-sized. It is likely that we will start seeing damage in lawns soon, so now is the time to act!
Before treating your lawn, first check to see whether grubs are present. Look for any thinning or dying patches in your lawn and use a shovel to pull back the turf to look for grubs. If the grass is healthy with fewer than five grubs per square foot, an insecticide application may not be necessary. If the population is higher, you may want to consider applying an insecticide.
There are two things to know when using an insecticide to control European chafer: (1) there are products that do not work (Gamma-cyhalothrin) and (2) there are products that work only at certain times. Of the products that are effective for grub control, they are either preventive (Chlorantraniliprole and Imidacloprid) or curative (Carbaryl and Trichlorfon).
Preventive products are the most effective. They should be applied prior to egg laying (mid-May through July) so the chemical will be present when the eggs hatch.
Curative products target actively feeding grubs in the early spring or fall but they are more effective against smaller larvae. Thus, an application now will be more effective than one later in the fall or next spring when the grubs are larger. The curative products break down quickly in the soil and will kill the grubs at any life stage, though often a treatment with a preventive product the following summer will be necessary for complete control.
Finally, when applying any of these products, you must water it in. You need the chemical to reach the layer where the grubs are feeding. This will require irrigating with a ½-inch of water after the insecticide application.
When applying an insecticide, remember, the label is the law. Make sure that any product you apply is approved for use against grubs in turf. Wear protective clothing required per the label including rubber gloves and rubber boots when applying the insecticide and keep children and pets away from the treated area until the grass is dry.
This is the first year that we are seeing extensive damage to lawns in Door County due to the European chafer. The battle has begun, but the outcome is not decided. Checking your grass for grubs and treating with the appropriate product at the correct time can keep your lawn looking great throughout the whole summer.
For more information on the European chafer and how to control it in your lawn, contact Annie Deutsch, Door County Agriculture Agent, by email at [email protected], by phone at 920.746.2263 or visit door.uwex.edu/horticulture/.