Sample turf for grubs and sod webworms

Have you ever seen a lawn ravaged by raccoons, skunks or crows? These critters don't cause this damage to be mean; they're just looking for food. What kind of food? In many cases, it's the larvae of scarab beetles, better known as white grubs. Or perhaps sod webworms. Several vertebrates consider these common turf pests a delicacy.

Control of white grubs and sod webworms starts with effective scouting and sampling. These are the hallmarks of a sound integrated pest management (IPM) program. With proper identification and knowledge of where the pests reside, you've won half of the pest-control battle.

Lawn-care operators vs. grounds managers Grounds managers, golf superintendents and lawn-care operators alike can take advantage of scouting and sampling techniques. If, for example, you manage 25 acres of hospital grounds, you may be responsible for many landscape activities. You may feel you don't have time to devote specifically to scouting. However, keeping an eye out for signs and symptoms of pest infestations during your normal routines can provide information critical to pest control. Over the course of a year, you'll get to know those 25 acres pretty well and should have no problem spotting infestations.

Time is even more critical for LCOs, who service many clients. Regular and thorough inspections of each one of your contracted lawns is usually not practical. In most cases, a reasonable approach involves carefully inspecting new accounts, then relying on the observations of your applicators or technicians as well as customers to help you assess the need for re-inspection.

Don't underestimate the benefits of scouting, however. If you are an LCO, every pest infestation you identify provides your customer a valuable service. Fickle clients change companies on a whim, and each value-added action you take distinguishes your company from your competitors.

Think back to the cost of landing that customer in the first place. You advertised and spent time making your sales pitch. You created a positive image through employee training, purchasing new trucks and using clean equipment. Now that you've got the customer, it's all about providing superior service to build customer loyalty.

Where to look You've heard the old story about looking for a lost coin under the street light? It wasn't actually lost there, but the light sure was better! The folly of this story points out the importance of looking for grubs and webworms in the right place.

The easiest and surest way to locate pests is to look where symptoms of injury occur. For grubs, these symptoms include browning and thinning turf in irregularly shaped patches. Grubs feed on roots and organic matter at the soil/thatch interface, which separates the grass blades and crown from the underlying soil. This causes the turf to take on a soft, spongy feel when you walk on it.

White grub "hot spots" can range from 2 to10 feet in diameter (sometimes larger) and occur most often in full-sun areas. Grubs may be present elsewhere in the landscape, but stressed turf is more susceptible and shows infestations before other areas. Ten grubs feeding in a hot, sunny area will cause considerably more damage than those same 10 grubs occupying a less stressful, semi-shaded location.

Sod webworm damage also appears as generalized browning and thinning of the turf. However, instead of irregular patches, it usually shows up more uniformly and over much larger areas. Sod webworm damage often has an appearance similar to fungal diseases, such as Bipolaris leaf spot/melting out.

One helpful trick for locating grub and webworm infestations is watching for bird and animal activity in the turf. In addition to foraging by raccoons and skunks, birds such as starlings, crows and other blackbirds are attracted to the grubs and webworms. If more than a few birds are pecking at the turf, the observant grounds manager or LCO will investigate.

Additionally, look at the areas where grubs and webworms have been a problem in the past. Areas with a history of damage are more likely to be re-infested year after year. Slopes, full-sun exposures and locations close to streetlights, sidewalks and driveways also are more likely to be infested.

Timing: when to look Look for pests at the right time of year. Review the life cycle of each potential pest to determine when it is active in your region, and sample accordingly. Information on turf-insect biology and management is available from several books, or you can obtain it with a quick call to your local Cooperative Extension office.

Most grub species associated with turf have only a single generation (and feeding period) each year. The active period may occur at different times depending on your location and the grub species involved. Thus, you'll need to monitor and sample accordingly. However, you can expect symptoms during the summer months when turf stress increases and grubs become larger.

Sod webworms, like grubs, injure turf during their larval (caterpillar) stage. However, because these insects can have several generations per year, the potential for injury throughout the growing season is considerable. Most sod webworm species overwinter as larvae and cause some damage to the turf in spring. After completing larval development, they pupate and transform into non-feeding adult moths. These moths start laying eggs in early summer. Because the life cycle for sod webworms is relatively short, three to four generations per year are common. Because of this, you must monitor for webworms throughout the growing season.

Inspection tools As with any other turf maintenance activity, you need appropriate tools for scouting and sampling. For grubs, a sod spade or shovel or golf-course cup cutter may be useful. For webworms, you'll need a pocketknife and some lemon-scented dish detergent.

If you have a suspected grub "hot spot," reach down and grab a handful of turf, pulling upwards. If the sod pulls loose from the underlying soil with little effort, then it is likely that grubs have eaten the roots of the turf (see photo, top of page 60).

Peel away the sod, looking for grubs just below the thatch layer and in the top 1 inch of soil. They should be easy to spot-white and C-shaped with a brown head and six distinct brown legs. Count the number you find within a 1-square-foot area.

If you want to get an idea of grub numbers before this level of damage occurs, you can dig out small sections of sod with a spade and examine the soil for grubs. Do this with care so that you can replace the sod with a relatively undisturbed appearance. Cup cutters also are useful tools for this procedure.

The species of grubs is often irrelevant to the decision of whether to treat, although certain grubicides are less effective against some species. If you would like some idea of which grubs are present you can identify them by their rasters (the posterior ends, which bear distinguishing patterns). Check with your local extension office for references relating to grub identification.

Sod webworms can be tougher to locate. First, they are generally smaller the white grubs-usually only about 0.5 inch or so in length. Second, they are typically the same color as their surroundings, a light green to tan hue. Finally, they hide in the thatch, burrowed in a tunnel and encased in a debris-covered silken web.

To coax them to the surface for easier identification, mix up a disclosing solution of lemon-scented liquid dish soap (about 2 tablespoons per gallon of water). Mark off 1 square yard of turf and pour about 2 gallons of this mixture over the turf, letting it soak in (see photos, page 60). In about 10 minutes, webworms will wiggle their way to the surface to escape the irritation of the mixture.

Treatment thresholds If you find large numbers of pests, the next step is to consider the appropriate control. This depends heavily on the treatment-threshold level, which is determined by the degree of damage you're willing to tolerate and how vigorous (and therefore tolerant of injury) the turf is.

No hard-and-fast rules exist for threshold levels, and published recommendations can vary. In high-maintenance turfs such as golf courses and high-visibility businesses, the threshold may be relatively low. In lower-quality turfs such as parks or cemetery grounds, it may be higher. You may, over time, be able to develop meaningful thresholds that work well at your site.

Whatever the threshold, when the number of pests exceeds it, then controls are warranted (see table, above, for examples).

Record keeping Record keeping is important for effective control of insect pests, especially in a year-to-year management strategy. When you encounter pests, record in your maintenance log the species, date of infestation, location, infestation level and whether you used control measures. You may want to note weather conditions and accumulated rainfall amounts because these can influence pest levels. Patterns and relationships between weather and infestation levels may help you predict future infestations. Writing notes takes only a few minutes, but will be invaluable in the future.

Often, infestations recur in the same areas year after year. Record keeping helps identify and keep track of hot spots, which allows you to anticipate future infestations. Early detection and timely treatments are powerful tools in your pest-management arsenal (see "Preventive grub controls," page 59).

Record keeping also helps you prepare maintenance budgets. If you know in advance that certain areas are likely to be infested, you can allocate adequate funds for treatment.

Scouting and sampling are critical steps in the overall pest-management process. They are the difference between making decisions blindly and making them intelligently.

If you notice damage, but sampling reveals no insect pests, look at other causes for the observed damage, such as pathogenic diseases, salt buildup, soil compaction and traffic. These can be easy to confuse with insect damage. Be sure you know the cause of the damage before taking action. An unnecessary application is wasteful and is a disservice to your client or employer.

Dr. Frederick P. Baxendale is professor or entomology and extension specilist, and John Fech is an extension educator, both at the University of Nebraska (Lincoln, Neb.).

Newer grub-control products such as halofenozide (RohMid's Mach 2), imidacloprid (Bayer's Merit) and the soon-to-be-available thiamethoxam (Novartis' Meridian) work best on small grubs. Using them effectively requires a more preventive than curative approach. Apply them when grubs are still tiny, or even before they hatch, in late spring or early summer. Avoid the temptation to apply these products "wall-to-wall." Monitor to predict future problems.

Existing infestations may be painfully obvious without deliberate monitoring. Because infestations often recur in the same location year after year, sites with a history of heavy populations and damage are good candidates for future preventive applications. However, regardless of prior history, if you sample in late summer (when grubs are large enough to find and count) and find worrisome levels, it's a good bet you'll have similar or higher levels the following year, which may warrant a preventive treatment.

Want to use this article? Click here for options!
© 2020 Penton Media Inc.

Interactive Products

Equipment Blue Book

Used Equipment Valuation Guide

Riding mowers, lawn tractors, snow throwers, golf carts


Grounds Maintenance Jobs

search our jobs database, upload your resume