Top turfgrass managers constantly watch and evaluate the turf under their care. While this is monitoring in a sense, what is missing is good record keeping. Regular and consistent record keeping will keep problem locations top of mind, and can provide timely reminders about when and where pests generally appear.
Step 1: Mapping
Maps help all types of turfgrass managers (golf course, lawn care, grounds, sod producers and sports fields) determine where and when certain pests regularly appear. Pests rarely occur evenly dispersed in turfgrass habitats. Turfgrass areas, even within the same facility, often have different types of soils or root profiles; areas differ in their irrigation and drainage; certain areas receive more stress that others (thinning from play or practice, soil compaction, etc.); surrounding habitats can differ (trees, shrubs, bleachers, lighting, etc.); and the grasses used can differ and even change over time. All these factors influence the incidence and severity of weed establishment, disease severity and insect attack.
Most facilities have some kind of map that was used during construction or renovations. Even if these maps don’t exist, you should be able to get high-quality images from Internet sources, such as Google Earth. I normally recommend each individual field be printed out on standard notebook paper and placed in a ringed binder. Make multiple copies. You can draw on each map where you encounter trouble with weeds, diseases or insects. Some use one map for cultural problems (irrigation issues, wear, poor drainage areas, etc.), another for diseases, one for weeds, etc. In a couple of seasons, it will become evident that certain areas consistently have the same issues. This will allow you to consider prevention actions for these areas or seek help on how to repair or change these areas so they are less prone to problems in the future.
Step 2: Monitor weather conditions
It can be difficult for mangers to get in the habit of keeping weather data on a consistent basis. More importantly, weather logs should also contain entries about weed, disease and insect activity observed. You may think that you need your own weather station, but experience has shown that using local radio or TV reports can be as useful as having your own station. If you want a weather station, note that they have dropped in price and many are relatively maintenance free and can be wirelessly linked to a computer where the data is stored and degree-day calculations can be made.
Many turfgrass diseases have weather-mediated triggers, and there are programs that evaluate rainfall, humidity and temperature. These are often major determinants of disease outbreaks. Several turfgrass insects have degree-day predictive models, and weeds, like crabgrass, have models that predict seed germination.
An even “lower-tech” method can be used to monitor weather: observing plant phenology over the seasons. Plant phenology is simply the sequence of noticeable plant events that occur during a season. As an example, red maples bloom first, followed by star magnolias, followed by forsythia bloom, then crabapples, etc. What is interesting is that other pest events tend to occur at the same time these plant events occur. Bluegrass billbug females begin to lay eggs when bridal veil spirea is in bloom, and Japanese beetle eggs are in the ground when Rose of Sharon begins to bloom.
We know that white grub populations generally increase when rainfall occurs in July, when the grub adults are laying eggs. These eggs need soil moisture in order to develop. Where general-use fields are allowed to go dormant in July, grub risk is low. However, if a field is being irrigated during this time, grub populations are always a risk.
Using a soap solution to sample caterpillar populations.
PHOTOS COURTESY OF DAVID J. SHETLAR, PH.D.
Step 3: Use insect sampling tools and techniques
There are simple and difficult methods of sampling insect populations in turf. The key to sampling is to get numbers that can accurately detect and measure populations that may result in significant turfgrass damage. We have already mentioned one of the easiest sampling tools, maps and your eyes.
It has been shown that areas that suffered white grub damage have an approximately 80 percent chance of repeat damage the following season. If billbugs have been an issue, it is generally because the type of turfgrass being used is susceptible. Without changing the turf, the billbugs will persist in attacking the same area year after year. The primary pests of most sports fields across North America are white grubs, billbugs, mole crickets (southern states), caterpillars (mainly armyworms in southern states) and ants (especially on skinned surfaces or fire ants in southern states).
This heavy infestation of grubs could have been detected earlier by using a cup cutter.
White grubs: In general, white grubs eat organic matter. Newly established turf usually lacks organic matter (thatch) in sufficient quantity to support large grub populations. Experience has shown that managed turf generally requires four to six years of thatch accumulation before it becomes “supportive” of grub outbreaks. Therefore, part of managing white grub risk should also entail keeping records of thatch buildup. The other thing that needs to be watched is grub adult activity. Where Japanese beetles are common, it should be evident that the adult beetles are emerging from the turf and/or they are feeding on nearby trees and shrubs. On the other hand, night-flying grub species (masked chafers, European chafers, May-June beetles, etc.) are best monitored using an insect light trap. However, turf managers have used a bucket of water placed under a facility light or light post. Beetles that land in the bucket can be observed and counted in the morning.
Entomologists often recommend more active grub sampling techniques, but sampling the soil for grubs usually isn’t effective until after the grubs have reached the second instar stage. At this time, mid to late August, grubs are more difficult to control with many of the insecticides, especially the less toxic ones. Some sport turf managers, especially those that work for parks, municipalities and school districts, are often asked to avoid using pesticides unless they can show that applications are needed. In this case, the simplest tool to use is a golf course cup cutter. This tool pulls a 4.25-inch-diameter plug of turf and underlying soil. This is approximately 1/10 of a square foot, which makes calculations easy to make. A crew of three samplers (each with a cup cutter) with another crew member recording information is recommended to perform the sampling. Such a crew can sample a football, soccer or baseball field in an hour or less. The process is to spread the core pullers evenly across the field. Take 10 paces and pull a plug. You only need to get about 2 inches of underlying soil. Turn the plug upside down and split the soil towards the grass on top. If any grub is present, it will usually be exposed at the soil-thatch interface. Turn the plug 90 degrees and split it again. The number of grubs found is hollered to the recorder, who puts the numbers on a map of the field. Put the plug back in the hole, tamp and move another 10 paces to repeat the process. Areas that have two or more grubs per plug are most likely to have turf loss and curative treatments are needed. Using this method, it is easy to determine if entire fields need to be treated or only portions of fields.
A fall armyworm larva that has surfaced after the spot was flushed with detergent water.
Billbugs: Billbugs can be more difficult to sample because of their small size. There is also an important difference between having bluegrass billbugs that attack cool-season turf or hunting billbugs that primarily attack bermudagrass and zoysiagrass. Since bluegrass billbug larvae burrow into grass stems, the telltale symptom of dead stems that are filled with sawdust frass can be utilized. However, hunting billbug larvae often feed on stems, rhizomes and crowns outside of the plant.
Hunting billbug adults often walk across the turf and hard surfaces late in the day.
For bluegrass billbugs, one can perform the “tug test” in early to mid-June. Simply grasp what looks like dying seed stems and pull. If they break easily and the broken ends are filled with sawdust-like material, you have billbug larvae present and feeding. If half of your tugs have damage, you could have significant turf loss, especially if drought conditions occur. Hunting billbug larvae are better sampled using the cup cutter method described for white grubs. For hunting billbug zones, it may be easier to watch for the billbug adults walking across sidewalks and driveways late in the day, or setting out pitfall traps that are described in most of the turfgrass insect books.
Mole crickets and caterpillars: It may seem strange to include these two insects together, but their sampling uses the same method, and both mole crickets and armyworms are more warm-season turf issues. The easiest method for determining population numbers is to use a disclosing solution of detergent water. Simply use one tablespoon of dishwashing detergent per gallon of solution. Joy Ultra, Dawn Ultra and Ivory Clear seem to be the detergents with the least potential for causing turf burn, even at two to three times the recommended rates. Other detergents occasionally cause yellowing of the turf. Two gallons of soapy water sprinkled over a square yard of turf will cause armyworms and cutworms to surface in minutes. When sampling mole crickets, this rate will bring up young mole crickets (generally from May through mid-July), but a double application may be needed to bring up large nymphs and adults (August through October), especially if the soil is dry. Damaging populations of caterpillars and mole crickets can usually be visually identified, but the detergent flush helps get actual numbers of insects per unit area. On sports fields, mole crickets and caterpillars are often common under and around lights, especially field lights that are left on well after play has stopped. Mole crickets are also attracted to soils that stay moist, so inspect and sample areas around sprinkler heads and where sprinkler patterns overlap.
Using a cup cutter to sample white grub populations.
Ants: Fire ants are relatively easy to monitor by locating visual mounds and marking the locations on maps. It usually becomes evident that mounds are concentrated in certain areas, often where trees may be located, fencerows, snack facilities, etc. Baits can be broadcast or applied around specific mounds where ant activity is prominent. The turfgrass ant in skinned areas can be monitored by simply counting the number of mounds between the bases or by using some other unit of measurement. Thresholds that require treatment are up to the facility manager. In some fields ant mounds are tolerated or knocked down before play. On other fields, user standards may require complete elimination of the ants. Remember that ant mounds in the skinned areas are merely a symptom of the ant colonies that are actually located in the adjacent turf. In other words, treatments will need to be made in a 15 to 20-foot band in the turf, not the skinned surfaces.
Get into the habit
IPM practitioners need to get into the habit of sampling and recording pest problems. If you have maps and record sheets, you will be more likely to record where and when pests occur. Sampling and monitoring takes time, but accurately knowing where pests are active can be the key to reducing pesticide use and achieving excellent control.
David J. Shetlar is professor of urban landscape entomology The Ohio State University, Ohio Agricultural Research and Development Center & OSU Extension.