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Identifying and Controlling the Pests of Turfgrass

Dept. of Entomology and Plant Pathology, Oklahoma State University

Numerous insects can cause damage to a wide variety of turfgrasses in the United States. Insect problems can vary greatly depending on geography and the type of turfgrass being grown. When managing any turfgrass problem it is best to accurately identify the underlying problem. Some insects cause damage to turfgrass that can appear as either a disease or a fertility problem.

In addition, many insect problems occur periodically rather than annually and preventive measures are not always required. The presence of adult insects in early spring does not always indicate that a wide spread infestation of that insect will occur later in the summer. It is always best to have an active monitoring program for insect populations if you suspect a problem rather than making unwarranted insecticide applications. Some of the common insect problems encountered in the turfgrass landscape include, armyworms, billbugs, chinch bugs, mole crickets, sod webworms, and white grubs.

Armyworms

PHOTO COURTESY OF Walker & Royer

The armyworm is usually 2 to 4 generations per year, depending upon geographic location and they take about 30 to 40 days to grow from egg to adult moth.

Armyworm is a term used for the caterpillar stage of various moths. These caterpillars are smooth skinned, robust caterpillars that measure about 1 1/2 inches when full grown, and tend to move in large numbers much like a marching army once they have depleted a food supply. There are a number of armyworm species that attack turf grasses, but the most common are the "true" or "common" armyworm, the fall armyworm and the lawn armyworm. Armyworms damage turf by chewing on leaves and stems.

Early signs of armyworm feeding may appear as "windowpane" feeding on the leaves. When armyworms reach full size, they chew the stems and leaves of individual plants down to the crown. The "true" armyworm is a gray to greenish colored caterpillar with two pale-orange stripes along each side of their body. It is mainly a pest of small grains, row crops and pasture, but during heavy outbreaks, they move into turf once they have depleted their preferred food hosts. They generally occur in damaging numbers in spring.

Fall armyworm caterpillars measures 1 inch when full grown and range in color from tan to nearly black. It can be distinguished from the "true" armyworm by the presence of a pale, inverted "Y" shaped marking on its head capsule. It gets its name because it does not overwinter in most of the U.S. and normally doesn't show up in damaging numbers until mid-summer or fall. They typically build in numbers in the south and migrate northward during the growing season.

They are more of a pest of turf in southern regions where they become active from July through November. They tend to prefer feeding on bermudagrass, but will also feed on fescue, bentgrass, ryegrass and bluegrass. The lawn armyworm is a pest of bermudagrass and zoysiagrass in Hawaii where it is considered one of the four major pests of turf. All three of these armyworms are sporadic pests because they are susceptible to numerous natural enemies, thus they are best managed with insecticides on an as needed basis. If detected early, they can be easily controlled with insecticides.

Billbugs

PHOTO COURTESY OF Robert Wright

Chinch bugs are often associated with hot dry weather that occurs during mid to late summer and can build up rapidly when such conditions persist.

Billbugs are found throughout the United States, and the damage they cause can be confused with other turf maladies. Billbugs in the United States include the hunting billbug in southern regions, the bluegrass billbug in areas where cool-season grasses are common, and the Denver and Phoenician billbugs in western regions. Billbugs are small (adults rarely exceed half an inch in length), are dark in color, and are weevils or beetles with a long snout. Most damage to turfgrass is caused by the larval stage which feeds inside the crowns, stems, stolons, and roots of plants.

The greatest damage occurs when larvae feed inside the crown which then kills the turf. Damaged grass turns brown and dies typically in small spots, but larger areas can be killed. Once the larvae become too large to feed inside plants they move into the soil where they feed on roots before emerging from the soil as adults.

The larvae, if found in soil, are white bodied and have brown heads and do not have any legs. The adults are commonly found walking on turf and can be seen walking across sidewalks and driveways. Sampling for billbugs can include water drenches, which cause the adults to float out of the turf, or by removing the sod and examining the soil for the larvae.

The thresholds for billbugs can vary depending on the situation, often ten per square foot is considered damaging. Biological control options can include planting resistant turfgrasses, using turfgrasses that contain a fungal endophyte, or applying the Steinernema nematode at high rates (1 billion/acre has shown to reduce populations). Chemical control as with any control measure, is best when conducted in the spring for billbugs. Consult literature or extension specialists in your area for thresholds and the best management options for billbugs.

Chinch Bugs

PHOTO COURTESY OF Walker & Royer

It damages turf because of its tunneling activities as it searches for prey.

Two species of chinch bugs, the hairy and southern chinch bug, are important pests of turf grasses and two others the buffalograss and "true" chinch bug are occasional pests. The hairy chinch bug attacks cool-season grasses (bentgrass, bluegrass and fescue) and is a pest mainly in the Northeast and upper Midwest. In general adult chinch bugs measure about 1/8 inches long and are black with a white "hour glass" marking on their back that is formed by their wings.

Immature chinch bugs can be recognized by the prominent white stripe that crosses the center of their body. The southern chinch bug is a severe pest of St. Augustinegrass grown along the Gulf Coast from Florida to Texas. It can also be found in southern California. The buffalograss chinch bug feeds only on buffalograss, and the "true chinch bug" feeds mainly on small grains corn and sorghum, and will only occasionally damage bentgrass, bluegrass, ryegrass, fescue or zoysiagrass.

Chinch bugs feed on various grasses by inserting their strawlike mouthparts into leaves and stems and drinking plant juices. They also appear to possess a toxic saliva that interferes with water and nutrient transport in the plant. Damage caused by chinch bugs may resemble drought stress. Plants become wilted, and yellow-brown in color. If left unchecked, large areas of turf can be killed.

Chinch bugs can be managed through practices that reduce thatch buildup. Some turfgrass varieties are reported to possess resistance and effective chemical controls are available. Control can be achieved if detected early through visual inspections. Use of a flotation cylinder will reveal harder to see nymphs. Turf can be monitored for chinch bugs with a floating technique. A suggested threshold of 20 to 25 bugs per square foot is used to determine the need for chemical control.

Webworm

PHOTO COURTESY OF Frank Peairs

Fall armyworm caterpillars measures 1 inch when full grown and range in color from tan to nearly black.

Sod webworms are common insects that cause damage to turf throughout most of the United States. A variety of webworm species are present in the U.S. and can prefer certain grasses over others. Some of the more common are bluegrass, elegant, larger, striped, tropical, and western sod webworms. Damage to turf is often most severe in new, stressed, or bluegrass lawns.

Adult moths hide during the day in vegetation and, if disturbed, fly short distances in an irregular pattern before landing. At dusk, moths can be seen flying across turf for greater distances. Adult moths lay eggs on leaves or drop eggs on the turf. Larvae hatch in a few days, feed at night, and hide during the day inside silk-lined tunnels constructed of leaf clippings, debris. Larvae can range in color from light green to grey to brown and are typically half an inch to a little over an inch in length.

Damage often appears as ragged turf, and in the absence of adequate water small brown patches may appear. Plant crowns are seldom damaged by feeding, and fertilization in combination watering can help lead to recovery; however, multiple generations can occur in a single year depending on location. Where populations are high, birds can often be seen feeding or searching for webworms.

The presence of sod webworms can be confirmed by mixing a small amount of detergent in 1 - 2 gallons of water and applying the solution to the turf. The soapy solution irritates the worms causing them to emerge briefly from their silk lined tunnels. Typically, populations between five and ten worms per square foot are high enough to require some management action to control the insect.

Mole Crickets

PHOTO COURTESY OF Oregon St. Univ.

A number of control options are available for sod webworms including using resistant turfgrasses, Bt products, and insecticides.

Mole crickets may be the most destructive of turf pests, especially in golf courses and sod farms. There are a number of mole cricket species, including the northern, shortwinged, southern, and tawny mole crickets. They have a cylindrical body that measures about 1 to 1 1/2 inches and is various shades of gray or brown.

The tawny and southern mole crickets are the most destructive. Mole crickets dwell underground and user their forlegs, which closely resemble the front paws of a mole, to dig tunnels. They are particularly destructive because they often go undetected until they become large and difficult to control. The tawny mole cricket causes the most damage to turf because it feeds on roots, stems and leaves of turf, while the southern mole cricket is predacious on various soil-inhabiting insects and earthworms.

Egg laying begins in spring and continues through June. They undergo one generation per year. Damage is most severe in late summer and fall, after the nymphs become full grown. Control is difficult, and usually requires scouting and mapping of the landscape to determine areas of high infestation. A good map saves time and increases the effectiveness of control by allowing insecticides to be applied to "hot spots."

Products applied before egg laying has been completed are less effective than waiting until egg hatch begins. A soapy water solution can be used to help determine when egg hatch begins. Control with insecticides must be timed properly for maximum effectiveness. Mole crickets are susceptible to Steinernema nematodes. A natural enemy has been imported and released in Florida, Georgia, and the Carolinas. Any management plan will require constant revision and attention to detail.

Grubs

PHOTO COURTESY OF D. Kindler , USDA,ARS

Moderate infestations of Weevils can cause small irregular patches of dead turf and heavy attacks (up to 500 per square feet) kills turf in large areas.

White grubs in the landscape feed on soil organic matter or underground turfgrass or other plant parts. Grubs are the different larval stages of numerous scarab beetles that are found inhabiting various regions of the country. The damage to turfgrasses caused by feeding can be found nearly everywhere; however, the most severe problems have been associated in northeast and upper mid-west states.

Some of the more frequently encountered grubs include the Japanese beetle, May or June beetle, northern and southern masked chafer, green June beetle, black turfgrass ataenius, and the oriental beetle. In addition to the direct damage caused to turfgrasses by grub feeding, extensive damage to turf can be caused by mammals such as skunks, armadillos, raccoons, opossums, and birds when they are foraging for the beetle larvae.

Most grubs are never seen above ground, and they remain hidden in the soil until they emerge as adult beetles. Life-cycles for grubs can vary based on geographic location; many life-cycles can be complete in a single year while others may take as long as three years to complete. When the grubs are resting in soil they have a characteristic "C" shape and a wrinkled appearance to the front half of the body.

When feeding, grubs often sever turfgrass roots near the plant crown resulting in plants that appear unthrifty, do not respond well to fertilization. Often the stand will thin and weed encroachment can be a problem. Under certain circumstances the turf can take on either a brown discolored appearance, or it can feel like it is poorly attached to the soil. The adult beetles can cause additional damage to the landscape; Japanese beetle damage to roses is probably one of the best examples of beetle damage to ornamental plants.

To confirm the presence of grubs it is best to peel back a strip of sod and examine the soil and thatch must for their presence. Depending on the grub/turfgrass combination, population thresholds vary widely from 3 to 20 grubs per square foot. Consult local literature or extension specialists for thresholds in your particular area and situation.

Management approaches can include commercially available biological control agents, insect growth hormones, or newly developed insecticides. Biological control agents, such as a bacterium which causes milky disease of grubs, has been used with some success for Japanese beetles. Parasitic worms or nematodes called either Steinernema or Heterorhabtitis have also been used with some success; however, biological control agents can require repeated applications and can have variable results.

New insecticides that have very low application rates and limited impact in the landscape have been introduced to the market in recent years for grub control. In addition, a growth regulating hormone which causes grubs to molt prematurely, causing it to starve to death as a result of poorly formed mouth parts has also been very effective in reducing populations. Regardless of the grub species present or management approach, controlling grubs is best done early in the season when they are smaller, cause less damage to turf, and are killed more easily.


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October 17, 2019, 9:24 am PDT

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