Billbug cool-season insect pests
Billbug. Photo by Geoffrey Rinehart

Insect Pests of Cool-season Sports Fields

By Geoffrey Rinehart

Integrated pest management (IPM) is a process of integrating several approaches to the management of insects with the goal of keeping damaging populations below threshold levels. For insects, these threshold levels are usually expressed as “individuals found per square foot” or “per trap” over a given period of time.

Some popular scouting techniques include soap flushes (helpful for cutworms, sod webworms and cranefly larva) and pitfall traps (for adult billbugs). It’s important to realize that many beneficial insects are at work regulating pest populations by way of predation and parasitism. Thus, successful IPM programs seek ways to preserve these beneficials by using targeted threshold levels and applying products that minimize off-target impacts.

Broad-spectrum products such as pyrethroids provide quick knockdown of pests that come into contact with the product, but these products can also knock back beneficial populations. Active ingredients such as chlorantraniliprole, tetraniliprole, spinosad and Bacillus thuringensis are more targeted to pests and have relatively little impact on beneficials within the turfgrass system.

Some varieties of tall fescue, fine fescue and perennial ryegrass contain symbiotic fungi called endophytes. Endophytes grow between cells of the turfgrass plant and can be transmitted via seed. These fungi help to impart some degree of drought tolerance, but, more notably, render the plant unpalatable to surface-feeding insects. Examples of surface-feeding insects include chinch bugs, billbugs, sod webworm, armyworms and cutworms (note: grubs are a “root-feeding” insect). It’s important to be aware that testing for endophytes may be inconsistent among seed companies, and those varieties that have been shown to possess endophytes often have their potency dissipate with time if seed is stored at high temperatures or for long periods of time.

Sound turfgrass cultural practices are the foundation for integrated pest management. In an increasing number of jurisdictions, pesticide usage on school grounds is being restricted, so it is especially incumbent upon field managers to implement proper cultural practices. Except for grubs and – at certain life stages – craneflies, most of the notable insect pests of cool-season fields are surface feeders. With this in mind, using turfgrass varieties that contain endophytes will go a long way toward preventing insect damage.

The population threshold levels represent ranges of pest populations. Typically, the turfgrass should be able to sustain populations in the higher part of that range if root growth is good and the sward consists of healthy plants. Cultivating to control thatch; aerifying to relieve compaction and allow better soil oxygen exchange; irrigating properly; ensuring adequate fertility for the species and use level of your field; and mowing at the high end of the mowing range (based upon the species and desired function of the field) all go a long way to encouraging a well-maintained, durable field that is more tolerant of pests. Overwatering, over- or under-fertilizing, mowing too low, or not cultivating can lead to unthrifty turfgrass swards that are most susceptible to insect pest pressures.

An important factor in limiting insect pest populations is the presence of beneficial predators. Beneficials are insects and other arthropods that provide natural control of pests when present in sufficient populations, and can be specific or generalists. Since many beneficial predators in a turfgrass system are generalists, fostering conditions that provide alternative food sources will help to ensure that they are present in sufficient populations to provide control during the time of year when pest insects are present. Research has shown that some beneficial predators’ alternative food sources are more available when turf is maintained at a higher mowing height. Mowing height should accommodate the intended use of the field and functionality of the playing surface, but mowing a little higher while accomplishing these goals is beneficial.


A primary group of insects found on cool-season grasses includes species of white grubs. This insect group belongs to the Scarab family of beetles and are turfgrass root feeders as juveniles (grubs). Common anatomical characteristics of grubs include a creamy white C-shaped body, six legs, and a brown-black head capsule. Grub species include Japanese beetles, masked and European chafers, Oriental beetles, May-June beetles, and Asiatic garden beetles. These species can be identified by their raster pattern, which is the arrangement of bristles and hairs located on the underside of their abdomen.

Throughout most of the northeast, transition zone and Midwest, the most common grubs are Japanese beetles and masked chafers. These are “annual grubs” that only go through one life cycle within a 12-month period. Beginning as an egg laid by females in mid-July to early August, grubs hatch and progress through three juvenile instars from August-September/October, growing progressively larger. With cooler autumn temperatures, grubs will travel deeper into the soil to overwinter as third instar larva. With warmer spring temperatures, grubs will slowly move further up in the soil profile and resume feeding on turfgrass roots before going into pupation in late May-June. They then emerging as adults, which feed on ornamental plants and mate by mid-July, starting the cycle over.

Damage and symptoms

Lighter damage may occur in the spring in areas with high grub populations, but turf damage is most evident in August through early October since cool-season grasses have fewer roots at the end of summer and additional stress from root-feeding grubs can compromise plant health. Damage can be worse in droughty summers. Symptoms of grub feeding include gradual thinning of the turf stand, wilting, yellowing/browning of turf, and irregular dead patches. Additionally, birds, skunks and raccoons may be observed digging up grub-infested areas, causing further damage. Dead patches will roll back easily (like lifting a carpet) since the grass roots have been eaten.

To monitor grub populations, cut a few square-foot sections of sod and peel back to examine the top 2” of soil and count the C-shaped grubs observed. Repeat this procedure in three to four samples around the field. If there is an average of 10-12 grubs/square foot or greater, a chemical control may be necessary (especially if the field has had grub damage in past seasons). Fields at or below this threshold can typically survive well with extra care in watering and making sure fertilizer applications and fertility levels are adequate.

If the field has had grub infestations from previous seasons, and monitoring in April/early May indicates populations above threshold levels, apply an insecticide labeled for season-long grub control in May. These products are applied to prevent grub infestation later in the summer, and include imidacloprid or the neonicotinoid alternative chlorantraniliprole. Additionally, an OMRI-certified product containing Bacillus thuringensis var. galleriae can be used as an “early curative” control. This product works best when applied at the first instar stage of the grubs (late July to mid-August).

Prevention and cultural practices

Cultural practices are a key to maintaining turfgrass health, enabling a field to lower pest pressures. Proper fertility and increasing mowing heights while still maintaining playability of the field will help grow a healthier plant and a robust root system that will withstand grub infestations better. Additionally, keeping the field on the “drier side” in the late summer and early autumn can be helpful by desiccating white grub eggs that are laid in July.

Chinch bugs

Chinch bugs feed by inserting their piercing-sucking mouthparts into leaf sheaths and crown tissue and suck out plant fluids, causing localized yellow or brown patches. Non-endophyte turfgrasses such as Kentucky bluegrass tend to be more susceptible to chinch bug feeding, and heat- and drought-stressed turf is the first to show damage. A majority of chinch bug damage occurs in mid- to late summer. For biological control, the big-eyed bug is the primary predator of hairy chinch bugs. Products with systemic activity (i.e., neonicotinoids or chlorantraniliprole) are recommended if spring adult populations are significant. Contact products can be used curatively.

Symptoms will include an irregular pattern of dead turf very close to healthy turf. The adult chinch bugs are very small (~1/6” long) and have a gray-black body, white wings, and reddish legs. Nymphs (juveniles) are smaller than adults and are orange to red with white bands across their back. Wing “pads” are present on the fourth and fifth instar nymphs. Monitoring for chinch bugs can be accomplished via soap flush — mix 3-5 oz. of dish soap in 3-5 gallons of water and gently pour this mixture onto the area where you suspect activity. Saturate the soil and wait a few minutes to observe insects floating to the surface. The soapy water will irritate them to emerge from the soil and then a count can be conducted. Research suggests that 15 to 25 chinch bugs per square foot may warrant control when chinch bugs are actively feeding in the summer.

Chinch bug damage is usually less noticeable in spring and early summer (the most noticeable damage usually occurs in late summer/early fall). Hairy chinch bugs have two generations per year in most locations. After adults emerge from overwintering in spring, they mate, and the adult females lay eggs in early summer. Second generation adults lay eggs from mid-July to late August and the second-generation nymphs (juveniles) develop in the fall.


There are several billbug species, but the bluegrass billbug and hunting billbug are the most common in turfgrasses. Damage symptoms resemble drought and can occur from late June to early August, so sometimes the damage goes unnoticed in dry conditions since it is difficult to distinguish from drought. The life stages that cause the most damage are the first two larval instar stages. Females lay eggs inside the turfgrass stem. When the eggs hatch, the first two larval instars tunnel through the stem and then feed on the crown of the plant and roots. Since the adults crawl along the ground, pitfall traps can be used to monitor activity. One important indicator of damage from early instar larvae is the presence of frass, created as the billbugs chew on and then excrete leaf stems.

Another way of identifying billbug damage is the “tug test.” If the turf leaves tug away easily and frass is present, this is a strong indication of billbug feeding. (Conversely, grub feeding will keep the lower stem and crown in place, but the turf will have very few roots.) Endophyte-enhanced grasses can be used to deter billbug feeding. Manage thatch to appropriate levels. Be sure to adhere to appropriate fertilizer and irrigation practices. In fields that have had high billbug pressure in the past, spring applications of contact or systemic insecticides can be made based on monitoring with pitfall traps and growing degree day models. Preventative applications are targeted at adults in May prior to egg lay.

Sod webworms and cutworms

Sod webworm larvae are tan/gray with small dark spots and brown heads, and reach ¾” to 1” fully grown. After overwintering as late instar larvae, the adults emerge as tan moths. Female moths of sod webworms fly just above the ground surface in spring in a zigzag pattern, laying eggs as they fly. The eggs land in the turf and caterpillars soon emerge. These caterpillars will feed on the leaf tissue just above the thatch layer.

Depending on your location, there may be different sod webworm species present and, thus, variation in developmental periods. The caterpillars are active at night and early morning prior to dawn, so this makes detecting them difficult. Symptoms include webbed tunnels in the thatch and green pellets (frass). Other symptoms include yellow/brown patches where the caterpillars have fed on the leaf blades. The preferred host is Kentucky bluegrass. Chlorantraniliprole and spinosad provide biorational control options for sod webworms. Pyrethroids such as bifenthrin, cyfluthrin and lambda cyhalothrin would be options for rescue treatments of these insects.

Cutworms are typically more of an issue on very low-cut turf such as golf course putting greens, but may occasionally affect sports fields. There are a few different species of cutworms (actually caterpillars) that can affect turf, but the common species include black, variegated and bronze cutworm. These caterpillars have a “pebbly” textured skin, and the black cutworm has a brown-earthen color tone, while the others are lighter in color. Black cutworms feed at night and burrow in the soil profile during the day. The presence of birds digging can be an indicator of cutworm presence. The most effective monitoring technique is a soap flush.

Damage includes clipping (cutting) turfgrass leaves off directly above the ground surface. Cultural control includes a few options. Females lay eggs on the tip of turfgrass leaves, so collecting these clippings and disposing of them far away from the field can help to reduce insect pressure. Biorational products for control include chlorantraniliprole (which also provides season-long grub control) and spinosad. Pyrethroids provide curative, contact-based control.

Insect pests of cool-season turfgrass
Fall armyworm damage to a tall fescue field without the endophyte (right) and a tall fescue field with endophyte (left). Photo by Dr. Kevin Mathias.

Fall armyworms

Fall armyworms are generally a relatively minor pest on cool-s

eason sports fields in the northeast and mid- to upper Midwest. Depending on the year, they have the potential to cause more damage for cool-season grasses in the transition zone east of the Rockies. The adults of the fall armyworms (which are in the same Noctuidae family as cutworms) overwinter in southern Texas and Florida and are blown northward over the course of the growing season by storms and wind currents from the south. Although typically not in large enough numbers to cause widespread damage to turfgrasses, in 2021 high overwintering populations and strong summer wind currents brought them north toward the end of the summer. Widespread damage occurred over areas that had never experienced that level of damage in decades. As a tropical insect, their life cycle slows dramatically with cooler nighttime temperatures in September.

Managing sports fields for reduced insect damage can be accomplished by optimizing IPM techniques. Selecting  turfgrasses that have improved insect resistance and  implementing proper primary cultural programs — such as  mowing, fertilization and irrigation — are the cornerstone  of IPM programs. Using control products based  on threshold levels, and that have minimal impact on  beneficial insects, will provide a high-quality sports turf  with fewer insecticide applications

Geoffrey Rinehart is lecturer, turfgrass management, Institute of Applied Agriculture, University of Maryland.

The author would like to acknowledge Dr. Kevin Mathias for his contributions to this article.


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