Let’s face it: It’s hard enough to combat turf pests when you know what you’re dealing with. But when one of the major pest groups has the ability to hide out, it makes things that much tougher. This is part of the reason turf problems caused by soil insects are commonly misdiagnosed. Another reason is that the damage caused by many hidden soil insects is often mistaken for other problems, such as drought injury, disease injury, soil compaction or poor fertility. If you can accurately diagnose their presence, a variety of control methods can help you effectively control these bottom feeders.
White grubs: a year-round pest
Found in all 50 states and in all types of turf, white grubs are some of the most common and most destructive soil-turf pests. They are the larvae of scarab beetles. They feed on turf roots and rhizomes and are capable of quickly destroying large areas of turf.
C-shaped with a light-brown-colored head capsule, white grubs are easily recognizable. You can identify the species of white grub you’re dealing with by using the rastral pattern located on the ventral side of the grub’s posterior end. Depending on your region, white grubs can have life cycles that fall into one of three categories: less than one year, one year, or more than one year, with the most common being a one-year cycle.
Grubs spend much of the winter in soil just below the frost line. As temperatures begin to warm, they head back into the root zone to feed and emerge as adults in late spring or early summer to mate. Their life cycle begins again when the adult females lay their eggs during the summer, which hatch into baby grubs that begin feeding on roots immediately. By fall, they have grown into much larger larvae and will continue to feed until November.
Grub damage often resembles moisture stress. Look for localized patches of pale, wilted, dying turf during the spring or fall that does not respond to irrigation. (See “Monitoring,” Page 22.)
White grub treatments: As with most turf pest problems, there are two schools of thought for grub control: preventive and curative. If you had an infestation of grubs last year, you’re likely to have them this year because grubs tend to re-infest the same sites. If you chemically treat to prevent them, it takes fewer chemicals to combat them in the large larval stage. That said here are options for either method.
Curative controls: These methods of treatment are relatively fast-acting, with a short residual time.
- Carbaryl (Sevin and other brands) is designed for use on actively feeding grubs that are near the turf’s surface. Rate of application will depend on the species you’re trying to control.
- Trichlorfon (Dylox and other brands) will hit young larvae feeding on turf roots. Evaluate thatch layer before application because more than 0.5 inch could prohibit good soil penetration. Irrigate following the treatment.
Preventive controls: These methods are just as effective as curative controls, but not as fast-acting. They do, however, have longer residual activity.
- Halofenozide (Mach 2) is formulated to help prohibit larval molting. While it does not immediately kill grubs, it does stop them from eating turf roots. You don’t have to irrigate following treatment because it is a systemic insecticide. Its long residual will affect hatching grubs for weeks.
- Imidacloprid (Merit) has such a long residual that it is well-suited for preventive control. Make applications at any stage of egg-laying – just be sure to water it in.
Billbugs: Act before it’s too late
With five species in the United States, there is pretty much a billbug for each region of the country. Adult billbugs are weevils, have long snouts, and aren’t nearly as damaging on turf as their larvae, which are small, white and legless. The larvae feed on the roots and stolons before working their way up into the stems and even crowns of turf.
While some billbugs have two generations per year, most are one-generation species. During the winter, billbugs will stay in a protected area, but come spring, they begin to move around to feed and mate, with females preparing to lay eggs in May and June. In Southern regions, larvae are most prevalent in early summer; in Northern regions, they’re most prevalent in July and August.
Billbug damage is often misdiagnosed as drought stress, dormancy or delayed green-up in the spring. It’s best to prevent billbugs by watching for adults in the spring.
Billbug treatments: If your client’s turf has suffered enough damage to warrant replacing it, you might research turf varieties that are resistant to billbugs, such as bermudagrass and zoysiagrass. If you are just trying to salvage turf for the season or you’ve salvaged turf and are hoping to avoid damage this year, look to a chemical application.
- Halofenozide (Mach 2) will work to prevent billbug larvae, depending on your region. Make applications when billbugs are laying eggs. The residual will work to control the larvae.
- Imidacloprid (Merit) can be effective against billbug larvae due to its long residual.
- Acephate (Orthene or Precise) and bifenthrin (Talstar) can be effective to control adult billbugs.
Monitoring, measuring and managing soil pests
To effectively treat soil insects, it’s critical to know when adults or larvae are present. If you’re familiar with pest life cycles, use that information to help determine when to monitor or sample for pests.
For billbugs, use a shovel to sift the top 3 to 4 inches of soil in areas of turf where there is visible damage. If you find more than 10 to15 billbugs per square foot, you are warranted to treat them. You can readily pull billbug-damaged turf out by hand because the stems break off at the crown.
Grubs won’t be distributed evenly in turf, so it’s important to sample thoroughly and consistently. Cut 6-inch by 6-inch sections of turf on three sides so that you can pull it back, examining the top 2 inches of root zone. Just because you don’t see any doesn’t mean your job is done. Keep sampling every 10 days or so, especially if you had a grub problem the previous year. If turf already has visible signs of grubs, verifying is easy: If you tug on a handful of turf blades and it pulls loose easily, you’ve likely got some root-eating grubs.