When it comes to controlling turf pests, casting a wide net with the wall-to-wall treatment approach is the way to go, right? Not really. There are a couple of exceptions: white grubs and annual grasses, which pests pose a significant enough threat to the health and vigor of the turf and are often year-in and year-out concerns, but for the most part, weeds, pathogens and insects should be handled on a case-by-case basis, treating only the affected turfgrass areas.
Why spot treatment?
Many sound reasons exist for using the spot-treatment approach. First, it saves money. If only 5 percent of the field is infested, the money that would have paid for the products to unnecessarily treat the remaining 95 percent can be redirected toward other projects, such as equipment purchases and soil improvements.
Spot treatments target pesticide applications directly to the pest, which is just common sense. It’s not reasonable to treat a section of turf where you do not expect problems.
When formulating new insecticides, manufacturers strive to develop products that have few, if any, undesirable side effects. One such side effect involves the harm that can come to nontarget organisms, including insect predators and earthworms. Another reason to utilize spot treatments is the reduction of injury to beneficial and non-pest species.
In addition, spot treatments save time. By not treating the entire field at predetermined intervals, treatments take only a fraction of the time needed to treat larger areas, and less time spent applying insecticide reduces labor costs for the overall budget.
Need for scouting/inspecting
Regular and systemic scouting of the field is necessary to make spot treatments effective. Over the years, the benefits of utilizing integrated pest management (IPM) as a turf culture and pest control strategy have been well-documented. Along with disease-resistant turf cultivars and appropriate soil modifications, regular scouting is a cornerstone of an effective, integrated approach to pest control.
A scouting schedule can be implemented as a stand-alone maintenance item, or it can be accomplished as you conduct other operations; always being on the lookout for symptoms of pest damage. For example, after a football game, it’s common practice to assign a 5-yard section of the field to each crew member to repair divots. Armed with a 5-gallon bucket of divot mix in one hand and an empty bucket to collect small chunks of sod in the other, workers scan the designated area from side to side looking for divots needing repair. Experienced crew members can simultaneously scan for symptoms of turf decline, flag them and return later to conduct a more thorough inspection.
A possible pitfall to employing a spot-treatment approach can occur if systematic scouting is not done on a regular basis. When inspections don’t take place, pests continue to develop and feed, causing more injury. Under these scenarios, a wall-to-wall treatment may have prevented the damage. Overall, however, the benefits of spot treatments far outweigh the “insurance” value of the preplanned, “spray by the calendar” approach.
Signs and symptoms
Although it may not sound like an important difference, there is a distinction between damage signs and symptoms. Symptoms are general, observable differences of color, shape or presentation of the turf stand, while signs are specific pieces of evidence that are linked only to certain insect pets. For example, a symptom that should attract one’s attention would be a patch of somewhat sunken, browning turf. Several turf maladies including diseases and abiotic causal agents could be responsible. Signs would be straw brown leaves, softened or chewed roots or the presence of an insect pest.
Signs and treatment of surface feeders
• Bluegrass Billbugs
At a distance, damage from billbugs appears as a general browning of the turf in patches from 2 to 10 feet in diameter. Grass stems appear shriveled, and affected areas are usually oval or roundish. Closer inspection reveals hollowed out stems and a sawdust-like frass material. These stems tend to easily break off in “tug” tests.
Control of billbugs typically involves applying insecticides in the spring to control overwintered adults before they can deposit their eggs. For adult billbug control, consider carbaryl or one of the synthetic pyrethroids (bifenthrin, cyfluthrin, deltamethrin, lambda-cyhalothrin). Apply insecticides to newly mowed turfgrass (collect and remove clippings) and lightly irrigate after applying to wash the insecticide off grass blades down to the soil surface where billbug adults are active.
Systemic insecticides can also be used to target the small larvae billbug while they are still feeding in the grass stems. These products include chlorantraniliprole, clothianidin, imidacloprid and thiamethoxam. An irrigation (.5 inch) following treatment will help move the insecticide down to the rootzone where they will be taken up by the plant.
Effective cultural practices can also significantly reduce billbug damage. Selection of adapted turfgrass cultivars and proper fertilization and irrigation programs will minimize the impact of billbug infestations.
• Sod Webworms
The general symptoms of sod webworm damage are similar to billbug injury. Signs of feeding injury include closely chewed stems, damage to the plant crowns and the presence of tunnels down into where webworms reside.
There are many products available for sod webworm control. For best results, apply insecticides in the late afternoon or early evening when larvae are active. Following application, the treated area should be lightly irrigated (1/8 inch), but delay heavy watering for 24 to 48 hours unless irrigation is indicated on the insecticide label. Granule applications also should be lightly irrigated immediately after application to wash granules off grass blades and activate the insecticide.
General turf damage from cutworms and armyworms appears as a generalized patch of yellowing or browning grass, often in midsummer through fall. Closer inspection reveals injury to the turfgrass crown; these insects usually feed in large numbers.
Sound cultural practices may allow healthy turf to withstand a moderate cutworm or armyworm infestation. In most cases, the turf will outgrow the injury. Generally, it takes fewer caterpillars to damage mismanaged or stressed turf. Overgrown and lodged grass in the vicinity of the turf area creates an ideal environment for later cutworm or armyworm infestation. When natural enemies and cultural practices are not sufficient to prevent damage and cutworms or armyworms are present, insecticidal control may be warranted. Insecticides labeled for cutworms and armyworms include those described for sod webworms.
• Chinch Bugs
Irregular patches of stunted and off-color turf caused by extraction of plant juices from leaf blades are the general symptoms of chinch bug injury. Often, a detection aid of lemon-scented dish soap and water is necessary to find the tiny insects responsible. Mix .25 cup of lemon-scented household detergent in 2 gallons of water over 1 square yard of affected turf.
If present, chinch bugs will come to the surface and be visible. Other insects such as billbug adults, sod webworms and cutworms may also be irritated using this step and come out of hiding as well.
Chinch bug treatments are most effective when applied while they are small. Before treatment, the turf should be mowed and the clippings removed, which will minimize interception of the insecticide by the turf canopy. Immediately following application, irrigate the treated area with 1/8 inch of water to wash the insecticide off grass blades and down into plant crowns and thatch where the chinch bugs are feeding. In turf stands where numbers are especially high, two insecticide applications may be required to achieve satisfactory control. Products labeled for chinch bug control include acephate, bifenthrin, carbaryl, clothianidin, cyfluthrin, deltamethrin, lambda-cyhalothrin, permethrin and trichlorfon.
• Greenbugs (Aphids)
From a distance, greenbug injury appears as a patch of yellowed, somewhat stunted turf. Telltale signs include leaves that are curled from side to side, with aphids present inside the deformed leaf blades.
Products labeled for greenbug control include acephate, bifenthrin, lambda-cyhalothrin and permethrin. Apply a liquid formulation of the selected insecticide to the greenbug infestation, including a 2 to 3-foot border around the damaged area. Thorough coverage is important. Do not irrigate for at least 24 hours following treatment.
John C. Fech is a horticulturist, certified arborist and frequent contributor located in Omaha, Neb. Frederick P. Baxendale is a professor and extension entomologist with the University of Nebraska-Lincoln.