by John C. Fech and Jonathan L. Larson, Ph.D
Insect pests can be a nuisance, a primary insulter or a compounding factor to go along with other causal agents in the overall scheme of things when managing turf on the golf course. In some cases it’s difficult to determine which category they fall into. In others a particular species may start out as a nuisance and develop into a more serious pest as the season progresses. In any event, following good integrated pest management (IPM) strategies is the key to keeping them in check.
The first step in turf IPM is scouting for pests. If root-damaging insects are in question, there’s nothing wrong with stooping down and digging through the dirt. Use a soil probe, shovel or cup cutter to get down to the root area. The pests you seek are usually in the top 6 to 10 inches of soil. Be sure to map the disturbed area and take samples in and out of the area of concentration. Make notes on the amount and location of pests found, and then compare the results with other samples to help decide whether treatment is necessary. These notes are good to have for planning purposes.
If you’re scouting for pests above ground, you can flush them out using irritants like lemon dish soap or a 1 percent pyrethrum solution. After mixing the solution, treat a square yard using a watering can to evenly distribute the mixture, wait 10 minutes, and then count the number of insects that appear.
You should have a set of criteria in place for when you turn to insecticide treatment. Once insect populations reach this number or damage levels go over the economic injury threshold you can consider your control options. Apply insecticides following label instructions, and ensure you’re applying the right product in the right place for the right pest.
Use the following general protocol to increase efficacy. Make applications during the evening when possible, as some chemicals may cause plant injury at temperatures above 100 degrees Fahrenheit. Always check a compatibility chart or the pesticide label before mixing two or more types of chemicals. Not all chemicals are compatible, and mixing may cause them to lose potency or burn plants.
When dealing with surface pests you should:
- Mow grass.
- Water well.
- Apply insecticide (sprays are preferred over granules) when plants are dry. Spot treatments are sufficient in some cases.
- Delay watering as long as possible.
For below soil surface pests you should:
- Mow grass.
- Apply insecticides (granular may be preferred).
- Water adequately to move insecticide into soil (full irrigation).
- A light pre-application irrigation will aid insecticide movement into soil.
Southern chinch bug: In addition to being of special interest to Carl Spackler, chinch bugs are a big problem for St. Augustine grass and occasionally a problem for those growing bermudagrass. This true bug is a double threat, in that both the nymphs and adults will attack by sucking out plant juices using their needle-like mouths. This feeding results in dwarfing, yellowing and eventually death.
The southern chinch bug is a small pest, ranging from 0.1 to 0.33 inch long, and as an adult is black with shiny white wings. Damage is most frequently seen at the height of the summer dry season. Chinch bugs have more than one generation per year and overwinter as adults.
Use the aforementioned water flotation method to detect an infestation. Preventive chinch bug control is dependent on good thatch management. If insecticidal control is needed, products containing carbaryl or any pyrethroid (e.g., bifenthrin, cyfluthrin, lambda-cyhalothrin or permethrin) are effective at controlling chinch bugs.
Rhodesgrass mealybug: The Rhodesgrass mealybug feeds under leaf sheaths, on nodes or in the crowns with their piercing-sucking mouthparts. Their feeding will interfere with water and nutrient uptake, resulting in stunting, thinning and death. Other symptoms include buildup of waxy white masses and possibly sooty mold. Mealybug damage is often heaviest in sunny locations during hot, dry periods.
Bermudagrass is only one species this insect may attack; St. Augustine grass, tall fescue and centipede grass can also be seriously injured. A nonchemical tactic is to collect and destroy grass clippings from an infested area. Chemical control will be difficult due to the waxy buildup on the insect, but products containing carbaryl, imidacloprid, bifenthrin, cyfluthrin or lambda-cyhalothrin provide control, but probably not eradication.
Bermudagrass mite: This diminutive troublemaker is found mostly in the southern U.S., where it damages bermuda by feeding under the leaf sheaths. They complete their life cycle in seven to 10 days, allowing for a rapid buildup of large numbers. Adult mites are elongated and banana-like in appearance, but are very difficult to observe with the naked eye. If an infestation is suspected, a close examination of the turf with a 10x to 30x hand lens may reveal the culprits.
The first sign of damage is turf that is nonresponsive to fertilization and irrigation and appears to be yellowing. Upon closer inspection managers will find that stem length between nodes is greatly reduced, and leaves and buds at the nodes may form a tuft. Damage is most severe during hot, dry weather.
Planting resistant hybrids is an option to prevent dealing with this mite. Physical elimination can be accomplished with close mowing and removal of clippings. Chemical control, with products like deltamethrin or bifenthrin, is difficult, since they hide under leaf sheaths. You should mow, irrigate the turf, and then spray the insecticide while the grass is still wet. A second application 10 days after the first may be necessary to obtain satisfactory control.
Two-lined spittlebug: Another double whammy pest, both adult and nymph spittlebugs feed by sucking juices from turfgrass. Adults are a little less than 0.5 inch long. Their bodies are black, their eyes and legs are red, and they have two distinct orange stripes across their back. As larvae they can be identified by the frothy spit that surrounds and protects them. This pest typically occurs in shady areas.
Symptoms include yellowing or small patches of wilted, stunted or dead turf. Cultural control practices that may help include reducing irrigation, limiting thatch, clipping removal and planting resistant cultivars. Acephate, azadirachtin, bifenthrin, carbaryl and deltamethrin can be used to control two-lined spittlebugs.
LEAF AND STEM PESTS
Armyworms: In turf we can deal with either fall armyworm or just the general armyworm. These are generally minor pests, but there is the potential for large outbreaks. Mature armyworms are 1.5 to 2 inches long. They range in color from gray to yellowish green and even pink.
True armyworms have a broken stripe down the center of the back and stripes along each side. Fall armyworms have an inverted white Y on their head. When young, they skeletonize leaf blades, but once they reach full size they consume all aboveground parts of the plant.
Populations are usually kept in check by predators, pathogens and parasitoids. If you catch armyworm infestations when the caterpillars are young, halofenozide, spinosad and Bt products will provide control. Insecticide options for larger armyworms include bifenthrin, carbaryl, chlorantraniliprole, insect growth regulators (IGRs) and lambda-cyhalothrin, amongst others.
Cutworms: Cutworms are typical caterpillars, more than 1-inch long when mature. Larvae are gray to dark brown with stripes running the length of their bodies. The name cutworm is derived from their feeding habit of cutting off young plants at or near the ground line, usually overnight. During the day they tend to hide in the thatch. When found during scouting they often curl into a tight C-shape. The adults are drab moths about 1 inch in size. The forewings often have wavy light and dark brown lines.
Mowing daily and removing clippings from greens, tees and surrounds can drastically reduce populations by removing eggs. If insecticide control is needed, chlorantraniliprole, pyrethroids, spinosad and IGRs are effective.
Fiery skipper: The fiery skipper is a type of butterfly that can be damaging to bermuda as a caterpillar. It has a very distinct appearance as a larvae, it is an army green color with a pronounced, bulbous head. They build silk homes in the turf canopy and emerge from them to create 1- to 2-inch-diameter spots of damage where they have consumed the turf.
Use the drench test to assess local populations. If damage is above economic injury thresholds, then you can apply spinosad, carbaryl or products containing Bt to kill the larvae.
Tropical sod webworms: Larvae of tropical sod webworms are cream in color with distinct red-brown spots on each body segment and a red-brown head. When mature, they are about 0.5 inch long. These caterpillars usually feed at night, consuming the surface layer of the grass blade. During the day they retreat to burrows in the thatch.
Damage appears as patches of brown, ragged turf that grow gradually in size. Birds, starlings in particular, are often observed feeding on larvae of sod webworms. Control with insecticides can be achieved with bifenthrin, carbaryl, halofenozide, chlorantraniliprole or Bt.
ROOT ZONE PESTS
Phoenix and hunting billbug: Billbug larvae superficially resemble white grubs, as they are creamy white with brown heads, but billbugs are smaller and legless. As adults both Phoenix and hunting billbugs are brown-colored weevils. Weevils differ from other beetles due to their elbowed antennae and pronounced nose, or bill.
As larvae they damage turf by feeding on the upper portions of the root system. Damage appears as a general yellowing and lackluster appearance. You may also find fine sawdust-like frass building up in the turf. The tug test is the best way to see if you’re dealing with billbugs. Grasp the turf between your fingers, and if it easily comes out then you are likely dealing with billbugs.
Control can be achieved when the billbugs are young by using commercially available nematodes or insecticides like imidacloprid, chlorantraniliprole or thiamethoxam.
White grubs: White grubs are the stereotypical root feeders that sever a sufficient number of roots to separate roots and shoots completely, creating sod that can be lifted up like a carpet. May and June beetle adults emerge from the soil in late spring, and then fly to turf and lay eggs beneath the soil surface. Seven to 10 days later, young grubs hatch and begin feeding voraciously on grass roots. They continue to feed until cool weather begins in mid-fall, when they burrow deeper into the soil. In the spring they move up towards the surface and resume feeding on roots. In late spring they transition to the pupal stage and shortly afterwards emerge as adults.
When used in spring or early summer when the grubs are young, treatments of chlorantraniliprole, imidacloprid, clothianidin, bifenthrin and others are the most effective.
Mole crickets: When growing bermuda, both the tawny and the southern mole cricket may become an issue. The tawny mole cricket is the more destructive of the two, as it feeds almost exclusively on the shoots and roots of grass, while the southern cricket is a predator. Both cause considerable damage by separating roots from turf with their tunneling. While they feed throughout the summer, damage is most noticeable from August until October, as the crickets reach adulthood.
Symptoms include pushed up turf and brown patches of dead grass. Use the soap and water mixture to sample for these pests as well as kill them as immatures. Possible insecticides include bifenthrin granules or acephate. Biological control is an option, utilizing the native Larra bicolor parasitoid wasp. By planting shrubby false buttonweed and partridge pea plants you can attract this wasp and suppress cricket populations.
Ground pearls: These scale insects attack the root zone of bermudagrass. They cover themselves in a globular, waxy layer and can be very damaging to warm-season grasses, especially in the South. Damage usually appears in summer, with the turf turning yellow in patterns resembling fairy ring. As fall approaches the turf turns brown and dies in patches, which then become infested with weeds.
Since there are no insecticides currently registered for ground pearls, prevention and proper turf care are your only control options. Always check new sod or sprigs for the pearls before planting, and try to manage turf stress as well as possible.
Jonathan L. Larson, Ph.D, is an entomologist with University of Nebraska-Lincoln Extension specializing in turf, tree, ornamental, nuisance and structural pest issues.
COVER PHOTO BY JAMES A. KALISCH