Chapter 15 Insects.
After studying this chapter, the student should be able to
* Diagnose turfgrass injury caused by insects
* Describe the ways in which insect pests injure turfgrass
* Identify the insect species that are serious pests of turfgrass
* Discuss the life cycles and characteristics of major injurious insects
* Explain how insect pests are controlled
Insects are small animals that have three pairs of legs. Adult insects always have six legs, but immature forms may not. Insect bodies are divided into distinct segments. The three major sections are the head, thorax, and abdomen (Figure 15-1).
Insects that feed on turfgrass have two different types of mouthparts. Some, such as grubs, caterpillars, and maggots, chew plant tissue. Their jawlike mouthparts tear, chew, and grind grass shoots and roots. Others, such as chinch bugs, scales, and aphids, have piercing-sucking mouthparts. They pierce plant tissue with their beaks and then suck juices from the stems, leaves, or roots (Figure 15-2). Both types of feeding can result in serious injury to turfgrass plants.
Insects have their skeletons on the outside of their bodies. This protective shell is called an exoskeleton. As insects feed and grow in size, the relatively rigid exoskeleton must be shed periodically or growth is restricted. Insects use chemicals to dissolve their old exoskeletons and then produce new, larger ones. This process is called molting. Each period between a molt is called an instar.
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The insect life cycle begins with an egg that is deposited on or near a food source, in this case a turfgrass plant. The egg hatches, and an immature insect emerges and begins to feed. This young insect is in its first instar. As it grows larger, the immature insect molts, enters the second instar, and continues feeding and molting until it becomes an adult. A female adult mates with a male and then lays eggs, beginning a new generation.
As insects progress through their life cycles, visible changes occur externally. Growth that results in changes in shape or form is called metamorphosis. Insects such as beetles, moths, and flies change tremendously in external appearance as they develop from egg to adult. They are said to undergo complete or complex metamorphosis. An immature beetle, for example, looks much different from an adult (Figure 15-3). Other insects such as chinch bugs, mole crickets, grasshoppers, and aphids do not change greatly in shape or form as they grow. They are said to undergo gradual or simple metamorphosis. An adult chinch bug, even though it is larger and has fully developed wings, appears similar to its immature version (Figure 15-4).
The immature stages of insect species that undergo gradual metamorphosis are called nymphs. Fully grown, last-instar nymphs molt and become adults. Three stages occur in the life cycles of these insects: egg, several nymphal instars, and adult. Immature stages of insect species that experience complete metamorphosis are called larvae. Fully grown, last-instar larvae are unable to simply molt and change into adults because the two stages are so different. Instead, the larva enters an inactive, nonfeeding stage during which it changes greatly in appearance and is transformed into an adult. This process is referred to as pupation. Four stages occur in the life cycles of these insects: egg; several larval instars, pupa, and adult (see Figure 15-5). The larva of a beetle is a grub, the larva of a moth or butterfly is a caterpillar, and the larva of a fly is a maggot.
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How seriously turfgrass is injured by insects depends primarily on the size of the insect population present in the turf area. Each individual insect consumes only a small amount of food because of its small size. The more insects that are feeding, the greater the injury to the turf.
The size of an insect population is influenced by several factors. Some insects have rapid reproduction rates, and large numbers can build up in a relatively short time. An insecticide application can kill many insects and decrease the population significantly. Weather has the greatest effect on insect populations. Weather conditions that are unfavorable result in smaller populations. For example, wet springs and summers contribute to a sharp reduction in the number of chinch bugs present in a lawn. In moist conditions a fungus disease destroys many of them. Most insects can complete their life cycles and lay eggs at a faster rate at high temperatures. The longer that temperatures are at optimal levels for insect development, the larger the populations.
In most regions of the United States insects overwinter in a resting state. They usually stop feeding sometime in the fall in response to the colder temperatures. When warmer weather returns in the spring, they become active and begin feeding again. In the warmest areas of the South insects may continue to feed throughout the winter.
The following species are the primary insect pests of turfgrass in the United States (Figure 15-6).
Figure 15-6 The major turfgrass insect pests in the United States. COMMON NAME SCIENTIFIC NAME Grubs Japanese beetle Popillia japonica May beetle (June bug) Phyllophaga spp. Southern masked chafer Cyclocephala lurida Northern masked chafer Cyclocephala borealis European chafer Rhizotrogus majalis Green June beetle Cotinus nitida Asiatic garden beetle Maladera castanea Oriental beetle Exomala orientalis Black turfgrass ataenius Ataenius spretulus Bluegrass billbug Sphenophorus parvulus Denver billbug Sphenophorus cicatristriatus Hunting billbug Sphenophorus venatus vestitus Phoenix billbug Sphenophorus phoeniciensis Tawny mole cricket Scapteriscus vicinus Southern mole cricket Scapteriscus borellii Short-winged mole cricket Scapteriscus abbreviatus Wireworms Various genera and species Ground pearls Margarodes spp. Hairy chinch bug Blissus leucopterus hirtus Southern chinch bug Blissus insularis Sod webworms Various genera and species Cutworms Various genera and species Armyworm Pseudaletia unipuncta Fall armyworm Spodoptera frugiperda Bermudagrass mite Eriophes cynodoniensis Buffalograss mite Eriophyes slyhuisi Clover mite Bryobia praetiosa Winter grain mite Penthaleus major Zoysiagrass mite Eriophyes zoysiae Bermudagrass scale Odonaspis ruthae Rhodesgrass scale (mealybug) Antonina graminis Leafhoppers Various genera and species Grasshoppers Various genera and species Greenbug Schizaphis graminum European crane fly Tipula paludosa Frit fly Oscinella frit Annual bluegrass weevil Listronotus maculicollis Ants Various genera and species Bees and wasps Various genera and species Periodical cicada Magicicada septendecim Black-legged tick Ixodes scapularis
Grubs are the larvae of beetles. The grubs of several beetle species, including the Japanese beetle, the May (June) beetle, the European chafer, the Asiatic garden beetle, and the oriental beetle, live in the soil and feed on turfgrass roots. These immature beetles are from 0.5 inch (1.3 centimeters) to 1.5 inches (3.8 centimeters) in length when fully grown, depending on the species. The soft, wormlike larvae are white to grayish in color, have hard brown heads, and have six distinct legs. They are often found curled in a C-shaped position in the soil (Figure 15-7).
Each of the species can be identified by examining the arrangement of the hairs or spines on the grub's raster, the terminal segment. A hand lens is necessary to distinguish the raster pattern (Figure 15-8). Species identification is important because some of these beetles have different life cycles and insecticide efficacy can vary between species. Turf managers are able to apply the best control product at the most effective rate when the grubs are most vulnerable if they know the species attacking the turfgrass.
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The majority of the beetle species that produce grubs that injure turfgrass have one-year life cycles. May beetles are an exception, completing their life cycles in two to four years. Japanese beetles are a typical example of the species that require one year to complete their life cycle (Figure 15-9). They spend at least ten months of the year in the soil. In the early summer the grubs pupate and become adults, leaving the soil to fly around and find mates. After copulation the adult females lay their eggs in the soil beneath grass sod. In July or August the eggs hatch, and the young larvae begin to feed on turfgrass roots. As the grubs feed, they molt and grow progressively larger. This rapid growth continues through the fall until soil temperatures become cold enough that the grubs stop feeding. They then tunnel down deeper in the soil and overwinter. In the spring, when the soil warms, the grubs move back up near the soil surface and resume feeding. In the late spring they reach full size and enter the pupal stage. After pupation the adults emerge from the soil, mate, lay eggs, and the cycle starts over.
Severe summer droughts have a major effect on grub populations. When the soil is extremely dry, many eggs desiccate and are destroyed. Grub problems are often minimal after a location has experienced droughty weather for several years unless it is irrigated, but the populations increase again when the soil is moist during midsummer. Unusually cool summer weather can result in a decrease in mating and egg laying. Extremely wet soil conditions can contribute to serious disease problems.
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Various beetle grubs attack many turfgrass species, but the adults do not feed on turfgrass. The leaves of trees and shrubs serve as their major food source. Japanese beetle adults can feed on more than 300 different plants.
Japanese beetles are most common east of the Mississippi River. Asiatic garden beetles and oriental beetles are a problem in the eastern United States. The European chafer is most serious in the Northeast. Masked chafers and May beetles are widely distributed in the United States. The green June beetle is a pest mainly in the South and transition zone.
Grubs have chewing mouthparts and are capable of causing extensive damage to the turfgrass root system. As few as five grubs per square foot (0.09 [m.sup.2]) may be enough to seriously injure the grass, especially if it is experiencing moisture stress. There is a direct correlation between the size of the grub and the amount of injury it causes. Populations of forty to eighty grubs per square foot (0.09 [m.sup.2]) of turf are not unusual.
When turfgrass suffers severe root loss because of grubs, the plants wilt, turn yellow or brown, and eventually die. Irregular patches of injured, dying turf appear. Grub damage can be diagnosed by examining the affected turf, which can be easily lifted from the soil if grubs are the problem. Grub-infested turf can be pulled up readily (Figure 15-10), because the roots are cut by the chewing mouthparts of the insects--the turf is no longer strongly anchored in the soil when grubs chew through the roots. Lifting the sod exposes the grubs. They are usually located in the top 3 inches (7.6 centimeters) of soil.
A quick survey for potential grub problems can be accomplished by cutting into the turf with a spade and examining the root zone. A golf green cup cutter can also be used to examine the soil. When the grub population averages more than five to ten per square foot (0.09 m2), insecticide treatment may be necessary. This decision is based on the species present, the health of the grass, irrigation capability, and other factors. A number of animals feed on grubs. The presence of moles or large flocks of birds feeding on turf areas is a good indication that grubs are in the soil. Skunks, raccoons, and other mammals will rip up the turf when searching for grubs (Figure 15-11).
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Grub damage is most evident during the spring (April and May) and fall (September to November). Insecticides are the primary method of control. Insecticide applications are most effective in July and August when the young larvae have recently hatched out. The grubs become less susceptible to insecticides as they mature. Frequent irrigation may also help the turf to recover. Daily watering will reduce the moisture stress caused by root injury and promote the growth of new roots.
The black turfgrass ataenius (BTA) is another beetle that produces root-feeding grubs. In Canada, it is known as the black fairway beetle. This species is known to occur in at least forty states, but it is less of a problem than the other grub species previously discussed. The injury caused has been primarily to annual bluegrass (Poa annua) on golf course fairways in northern states. Bentgrass and Kentucky bluegrass may also be attacked.
The adults, which are 0.1 to 0.2 inch (2.5-5 millimeters) long, overwinter along the edge of fairways in the soil or under tree leaves or other debris on the ground. In the spring the adults emerge from these protective sites. Eggs are laid in the soil or thatch beneath turfgrass in May or early June. The eggs hatch, and the grubs begin to feed on roots. The first instar larvae are so tiny that they are difficult to see with the naked eye. After feeding, molting, and growing for approximately a month, the larvae reach maturity and tunnel down into the soil to pupate in late June and July. A BTA larva has two distinctive pads on the tip of its abdomen. The adults appear in July and early August.
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In most areas a second generation occurs. The adults lay eggs in July and August. The second-generation larvae feed throughout the remainder of the summer and pupate in September. In September and October the second-generation adults leave the fairways and seek shelter for the winter.
The first wilting symptoms appear in mid-June and continue throughout the summer. Annual bluegrass is most severely injured. Because of the small size of the larvae, large populations are necessary to cause serious root-feeding problems. More than forty BTA grubs per square foot (0.09 m2) are required for significant damage to occur, unless the turf has been weakened by other stresses.
Billbug grubs feed on turfgrass roots, crowns, and stems. The adult beetles, members of the weevil family, have their chewing mouthparts at the tip of a snout or bill (Figure 15-12). The larvae are less than 0.5 inch (1.3 centimeters) long and legless, with thick white bodies and brownish heads. The Phoenix billbug attacks bermudagrass, the hunting billbug feeds on zoysiagrass, the bluegrass billbug is primarily a problem on Kentucky bluegrass, and the Denver billbug also prefers bluegrass plus perennial ryegrass.
Generally these species overwinter as adults, hibernating in the turf or nearby protected areas. In the spring the adult females lay eggs in the lower part of the turfgrass stem. After hatching, the larvae feed inside the stem and then feed on the crown. Eventually the grubs move down into the soil and attack roots and rhizomes. They change into pupae at the end of the summer or in early autumn, and the adults emerge from the soil in September or October. There is usually only one generation a year.
Injured turfgrass wilts and turns brown during the summer. Damaged plants are easily pulled up, especially if the grubs have chewed off the stems at the crown. The presence of a fine, white, sawdustlike material, known as frass, at the feeding sites on the turfgrass plant is evidence of billbug problems. Observing billbug adults on sidewalks, driveways, and other paved areas adjacent to the turf in the spring and fall is another method of detecting potential problems. Insecticides are applied either in the spring to prevent the adults from laying eggs, or in June to kill the newly hatched larvae.
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Mole crickets are a type of cricket that lives in the soil and feeds on grass roots, stolons and rhizomes, insects, and earthworms. They are a pest of many turfgrasses in the southeastern United States and Texas. Bahiagrass and bermudagrass usually receive the most damage. The southern and the tawny mole cricket are the two species that cause the greatest problems. Mole crickets are light brown, covered with velvety hairs, and have short, spadelike legs that are adapted for digging and tunneling through the soil (Figure 15-13). The adults are approximately 1.5 inches (3.8 centimeters) long. The mole cricket undergoes simple metamorphosis. Immatures are called nymphs.
Eggs are laid in the soil in the spring. The nymphs hatch out in May or June and look like the adults, except that they are smaller and lack fully developed wings. The nymphs live in the soil the remainder of the year and most of the southern mole crickets become adults the following spring. Tawny mole crickets usually reach adulthood by December. There is one generation per year.
Turfgrass may wilt and dry out because of mole crickets' root feeding and tunneling. As they burrow through the soil, plants can be uprooted (Figure 15-14). Damage can be severe, especially on newly seeded or sprigged turf. Mole crickets often burrow 6 inches (15.2 centimeters) or deeper into the soil. They are not found in heavy soils. At night, especially after a rain or irrigation, they come up near the soil surface to feed.
Insecticide applications give best control in the spring when the nymphs are small and relatively easy to kill. Spreading bait containing an insecticide on the turf is also an effective method of control. There is a great deal of interest in using natural enemies such as parasitic nematodes, wasps, and flies for control. This will be discussed in Chapter 17.
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Ground pearls are scale insects found in the southern United States. They secrete a waxy material that covers and protects their bodies like a shell. These shells, called cysts, are spherical and pearl-colored. The cysts are usually around 0.125 inch (3 millimeters) in diameter. Ground pearls have piercing-sucking mouthparts and suck juices from turfgrass roots. They attach themselves to the roots by penetrating the tissue with their needlelike beaks (Figure 15-15).
Ground pearls feed on the roots of centipedegrass, bermudagrass, zoysiagrass, and St. Augustinegrass. Their life cycle is not fully understood, but it is usually completed in one year. The adult females leave their protective shells and deposit eggs in the soil. The eggs hatch during the summer. The newly hatched nymphs, called crawlers, insert their beaks in roots and then secrete the pearllike shell around their bodies.
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Chemical control of ground pearls is very difficult because of the protective shell and because they may feed as deep as 10 inches (25 centimeters) below the soil surface. They injure the plants by removing liquids containing carbohydrates and minerals from the roots. The effect of this feeding damage can be reduced by fertilizing, watering, and mowing properly to keep the grass as healthy as possible.
Leaf and Stem Feeders
Two species of chinch bugs are important turfgrass pests in the United States. The hairy chinch bug attacks cool season grasses, and the southern chinch bug feeds on warm season grasses. The latter species is a serious threat to St. Augustinegrass. Hairy chinch bugs are primarily a problem in eastern and midwestern states. They injure plants by sucking juices from the shoots and by injecting a toxic salivary fluid into the tissue. This fluid damages the xylem, the water-conducting tissues, causing the plant to wilt and turn brown. If the weather is hot and dry, the affected turfgrass will die.
The number of generations that occur in a year depends on temperature. The warmer the temperature, the faster the chinch bug completes its life cycle. In the northernmost areas of the United States there are only one or two generations a year. In southern Florida there may be seven or more. Chinch bugs may continue to feed and be active through parts of the winter in warmer climates. In colder regions they overwinter as adults in tall grass or other protected sites, and begin egg laying in the spring.
Eggs are deposited on or in lower leaf sheaths, stolons, or in the thatch. Each female can lay over 200 eggs. The first instar nymphs that hatch from the eggs are the size of a pinhead, 0.05 inch (1.3 millimeters) long. They are bright red, wingless, and have a white band across their backs. There are usually five nymphal instars (see Figure 15-4). As these immatures molt and grow larger, their color changes to orange, then brown, and finally to black in the last instar. All of the nymphs have the white stripe, although it is partially hidden on the final-instar nymph. The adults are approximately 0.2 inch (5 millimeters) long and are black with white, folded wings (see Figure 15-16). The white wings have black markings.
Chinch bugs are commonly found in sunny areas. Heavily infested, sunny sites may contain over 200 chinch bugs per square foot (0.09 m2). Their damage becomes most apparent during droughty periods in the summer (Figure 15-17). People often mistake chinch bug injury for dormancy resulting from moisture stress because they expect the grass to turn yellow or brown during hot, dry weather. They become aware of the problem when the dead grass does not green up again after rain or irrigation. This misdiagnosis is a serious error because turf injury can be easily prevented by an insecticide application if the chinch bug infestation is discovered in its early stages.
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When suspicious yellow spots appear in a turf area during the summer, the turf manager should push aside the grass and examine the surface of the soil or thatch for chinch bugs. A careful examination is necessary because the insects may be difficult to see. They are small and will attempt to hide when disturbed. A simple method of detection is to remove both ends of a coffee can or similar large can, cut off or file one rim to produce a sharp edge, and twist and push the can 1 to 2 inches (2.5 to 5.1 centimeters) into the soil. It should be worked into the soil at the edge of a declining spot, preferably where the grass is just beginning to turn yellow. The can is then filled with water, and within five or ten minutes any chinch bugs present will float to the surface. It may be necessary to add more water to keep the water level above the grass. A plug can also be pulled from the site and dropped into a bucket of water. Flooding a small area and then covering it with a piece of white cloth also works. Chinch bugs will crawl up to the top of the leaf blades and then cling to the underside of the cloth.
Significant chinch bug populations, usually twenty or more per square foot, may require an insecticide application. Early detection and control protect the turf from serious injury. Insecticide applications do not completely eradicate the pest, but do result in a significant decrease in its population. In prolonged periods of wet, rainy weather, a fungus disease infects and kills chinch bugs. An insect predator, the big-eyed bug, feeds on chinch bugs (Figure 15-18). Floratam, a St. Augustinegrass cultivar, was widely used because of its resistance to chinch bugs, but it has become susceptible. Perennial ryegrass, tall fescue, and fine fescue cultivars high in endophytes are resistant.
Sod webworms are actually caterpillars, the larvae of moths (Figure 15-19). Several species of sod webworms injure turfgrass. The caterpillars chew the leaves of turfgrass plants with their mouthparts, but the adult moths do not feed on turf. The adults are usually referred to as lawn moths because they are often seen laying their eggs on lawns.
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The moths are grayish white to brown in color and 1 inch (2.5 centimeters) or less in length. They have two distinguishing features. The adults are sometimes called snout moths because of the snoutlike projection that extends from the front of their heads. When they are not flying, lawn moths fold their wings around their bodies (Figure 15-20). Most moths, when at rest, keep their wings spread.
The caterpillars have dark brown heads. Their size varies with each instar, but the full-grown larvae are approximately 0.75 inch (1.9 centimeters) long. The sod webworm's body is tan, green, or gray depending on the species. Most have black or dark brown circular spots scattered over their bodies.
In northern areas there are usually two generations per year; in southern climates the number is greater. This pest normally overwinters in the larval stage. In the spring the caterpillar pupates and becomes an adult. Female moths fly over the turf at dusk and drop their eggs randomly. During the day the moths hide in the grass or in shrubs and trees near the turf area. The caterpillars hide in the thatch during the day and feed on the grass foliage at night. As they grow larger, they construct silk-lined tunnels in the thatch.
The sod webworm injures grass plants by chewing off leaves. If the population is small, the damage is usually minor. Plants can often produce new leaf tissue and recover. However, the intense feeding of a large sod webworm population may result in a loss of turfgrass quality. This is especially true during periods of dry weather. Golf greens and other closely mowed turfs are more readily injured than areas where the grass is cut to a taller height (Figure 15-21).
If flocks of birds, especially starlings, return frequently to feed on a turf area, it may indicate an infestation of sod webworms or other larvae. Pencil-sized pecking holes made by birds when they are searching for larvae are another possible sign of insect problems. If close examination of irregular brown areas in a turf reveals that leaves have been chewed off, the turf manager should look for caterpillars in the thatch. During the day they are normally found curled up near or on the soil surface. The presence of green pellets of excrement, called frass, is also evidence of sod webworm feeding.
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Sod webworm and other caterpillars can be detected by pouring household detergent on any suspicious brown spots in the turf. The detergent acts as an irritant and brings the insects to the surface, where they can be seen more easily. A common mixture used is 1 ounce (30 millileters) of liquid detergent per gallon of water.
Most people become aware of potential sod webworm problems when they observe numerous lawn moths flying over the turf in the early evening. The moths may also be seen during the day because they fly out of the grass when disturbed. The presence of adults does not mean that damage is inevitable. It is best to check for larvae before applying an insecticide. Turfgrass can usually tolerate up to ten sod webworms per square foot (0.09 m2), unless it is cut very short.
The sod webworm population builds up as the growing season progresses, and turf injury is often greatest late in the summer. Damage is most likely on well-managed turf because the sod webworms are attracted to higher quality, vigorous grass. If insecticide treatment becomes necessary, an evening application is best because this is when the caterpillars emerge from the thatch to feed.
Cutworms are caterpillars with dark brown heads and blackish, gray, or brown bodies. They may have stripes or spots, depending on the species. Mature larvae are 1.5 to 2 inches (3.8 to 5.1 centimeters) long (Figure 15-22). Cutworms hide in their burrows in the soil during the day and feed at night on foliage. Larger instars chew off turfgrass shoots near the bottom of the stem. Usually they are only a minor problem, but golf greens, tees, and new seedings may occasionally be seriously injured. Even a small amount of damage is unacceptable on a green.
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The black cutworm (Agrotis ipsilon) is the most common pest on turf. There can be from two to six generations per year, depending on the latitude. The black cutworm appears to be unable to overwinter in northern states so adults fly up from the south or transition areas in the spring.
The female moths prefer to lay their eggs on the leaf tips of close-cut creeping bentgrass. Mowing usually removes at least 80 percent of the eggs, so it is important to discard the clippings away from the green or tee. Cutworm larvae can crawl 60 feet (18 meters) or more in a night.
Armyworms are caterpillars that are 1.5 to 2 inches (3.8 to 5.1 centimeters) long when fully grown. Their color varies from green to gray, and they have stripes (Figure 15-23). The caterpillars feed on grass leaves at night, but unlike cutworms and sod webworms, they often do not hide during the day. Large numbers of armyworms are usually found feeding together. This "army" devours one turf area and then crawls to another site at night. Armyworm problems are most common in the South.
Mites are very similar to insects, but they usually have four pairs of legs rather than three. Mites are extremely small, and a hand lens or microscope is needed to examine them. Enormous populations can build up in a short time because of their rapid reproduction rate. Some species complete their life cycles in a week. Hundreds of mites may be found feeding on a single grass leaf or stem. Leaves become blotched or spotted as mites suck the juices from the shoots. Continuous feeding by large numbers of mites results in the death of the leaves.
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The bermudagrass mite is a serious pest of bermudagrass in southeastern and southwestern states (Figure 15-24). It is very tiny, only 0.01 inch (0.25 millimeter) long, and feeds under the leaf sheaths. A microscope is necessary to identify these yellowish white, wormlike pests (Figure 15-25). Because they are difficult to see, their presence is often diagnosed by the characteristic injury they cause to turfgrass. Initially, the leaves of infested plants curl abnormally and turn light green. As the feeding continues, leaf tissue swells, stem internodes become shortened, and the leaves are crowded closely together on the stem (Figure 15-26). The injured plants have a clumpy or tufted appearance.
The clover mite and the winter grain mite are two other species that occasionally cause injury to turfgrass. The winter grain mite has an unusual life cycle because it feeds in the winter but not during the summer. Neither of these species is as important a pest as the bermudagrass mite. The buffalograss mite and zoysiagrass mite are also occasional problems.
Some insecticides will be effective against mites because they are close relatives of insects. Miticides, pesticides developed specifically to kill mites, can also be used. Chemical control may be necessary when mite populations are very large and the grass is suffering from moisture stress.
Scales are small insects that secrete a waxy material that serves as a protective covering. Ground pearls, scale insects that feed on roots, have already been discussed. Two other scale species are also pests of warm season turfgrasses. They suck plant juices from grass leaves and stems.
The bermudagrass scale, as its name implies, primarily attacks bermudagrass. It is oval or circular, 0.04 to 0.07 inch (1 to 1.7 millimeters) in diameter, and covered by a hard, white, waxy shell. The rhodesgrass mealybug, which is also called the rhodesgrass scale, feeds on bermudagrass, St. Augustinegrass, and centipedegrass. Its dark, spherical body, covered with a mass of white cottony material, is 0.125 inch (3.2 millimeters) or less in diameter.
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When eggs hatch, the first-instar nymph, called a crawler, is mobile and finds a place to feed on the stem or leaf. It then secretes its protective covering and does not move again. Scale infestations are easy to diagnose because of the insect's immobility and distinctive appearance.
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Leafhoppers are small, wedge-shaped insects that readily fly or hop around (Figure 15-27). The adults are normally 0.5 inch (1.3 centimeters) or less in length. The immature nymphs closely resemble the adults, but are smaller and lack wings. Leafhoppers are common, but do not often cause serious injury to turfgrass. Occasionally large numbers may migrate into a lawn and damage plants by sucking out fluids from the shoots. Usually they move on to another area in a few days. Most serious injury occurs in the prairie states.
Grasshoppers are chewing insects that commonly feed on range and pasture grasses, as well as grasses growing in waste areas. They are seldom a threat to well-maintained turf unless their numbers are quite large and food is scarce.
Aphids are small, piercing-sucking insects that are common pests of many plant species. However, until recently they were not considered a serious problem on turfgrass. In the 1970s one species of aphid began to cause extensive injury to Kentucky bluegrass on lawns in some midwestern states and since then has extended its range. These aphids are called greenbugs because the nymphs and adults have soft, pear-shaped bodies that are light green in color. The antennae, eyes, and tips of the legs are dark in color. These aphids are usually wingless, approximately 0.06 inch (1.6 millimeters) long, and have two tubes extending from their abdomens (Figure 15-28).
Greenbugs can become a serious problem because of their rapid reproduction rate. Females do not need to mate with a male. They give birth to living young during the spring and summer rather than laying eggs. At optimum temperatures, a greenbug is able to develop into an adult and begin reproducing a week after it is born. Populations build up very quickly, and thousands of these aphids may be found per square foot (0.09 m2).
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Greenbugs injure turfgrass plants by inserting their mouthparts into leaf tissue and sucking sap from the phloem. Further damage is caused by salivary fluids, which destroy the leaf tissue surrounding the area that is pierced by the insect's beak. Infested grass blades turn yellow, then orange, and finally brown when they die. Injury is most common during summer months, especially on turf areas shaded by trees. Greenbugs are thought to overwinter in the egg stage.
Diagnosis is simple because of the large numbers of greenbugs present on leaves when turfgrass injury occurs. Several insecticide applications are often necessary to control this pest. Many aphids will be killed by the insecticide, but some will survive. The greenbug's rapid reproduction rate enables the population to rebuild quickly unless insecticide treatment is repeated. Moreover, it has exhibited resistance to some insecticides.
Greenbug problems are most likely to be encountered on lawns that are heavily fertilized and treated regularly with insecticides. Prior insecticide treatments may have killed natural enemies such as lady beetles.
Frit flies are tiny, shiny black flies approximately 0.06 inch (1.6 millimeters) long (see Figure 15-29). The larvae, called maggots, tunnel into grass stems near the soil surface and feed on the tissue with their chewing mouthparts. During hot, dry weather the infested shoots are killed. The maggots are small, legless, yellowish white in color, and have two black hooks on their heads. These hooks are chewing jaws and can be seen with a hand lens.
The maggots overwinter in grass stems, and in the spring, after pupation, the adult flies lay eggs on turfgrass leaves. The newly hatched larvae tunnel into stems and begin to feed. Several generations occur each year. The principal hosts are close-cut bentgrass and annual bluegrass. Frit flies are common throughout the United States, but generally are a minor problem on turfgrass.
The adult flies are attracted to white objects. This curious habit aids in diagnosis. If present, they will immediately appear on a piece of white paper or cloth that is placed on the turf. Frit flies will hover around and land on a golf ball lying on an infested green.
[FIGURE 15-29 OMITTED]
Annual Bluegrass Weevil
The annual bluegrass weevil, which feeds on annual bluegrass, and occasionally bentgrass, is also referred to as the hyperodes weevil. This insect is a serious pest primarily on golf course fairways and collars around greens that contain significant annual bluegrass populations. It is a problem in the northeastern United States and some mid-Atlantic states. The adult weevils are black, have snouts on their heads, and are less than 0.2 inch (5.1 millimeters) in length. The larvae are also small and have soft, white, legless bodies (Figure 15-30). Their heads are brown.
The annual bluegrass weevil overwinters as an adult in protected sites under fallen tree leaves or needles or in tall grass in the roughs adjacent to infested fairways. Under white pine needle litter is a favorite spot. In the spring the adults crawl to the turf areas populated with annual bluegrass and lay eggs in the leaf sheaths. The larvae feed in stems initially and then feed on the crown of plants (Figure 15-31). Injury becomes apparent by late spring. Mature larvae pupate in the soil near the surface. There are usually two generations a year, though one occurs in more northern locations.
Insecticides are applied before the adult has laid its eggs in annual bluegrass stems. Treatment occurs before flowering dogwood and redbud full bloom because this is when the adults lay eggs between leaf sheaths.
Other Insect Pests
Other insects occasionally injure turf, although they do not feed on turfgrass plants. Several species of ants build underground nests in turf areas. As the ants excavate soil, grass plants close to the mounts are buried or desiccated. Anthills also disrupt surface uniformity (Figure 15-32).
The red imported fire ant (Solenopsis invicta) is found in the southeastern and southwestern states, California, and Puerto Rico. They are well known for their aggressive behavior when disturbed. Some people, when stung, are very sensitive to the venom. Fire ants also cause power outages because they chew insulation from electrical wires. Equipment can be damaged when it runs over the large mounds they build. Some bee and wasp species nest in turf as well, and people may be stung when they walk near the nests.
[FIGURE 15-30 OMITTED]
[FIGURE 15-31 OMITTED]
[FIGURE 15-32 OMITTED]
[FIGURE 15-33 OMITTED]
Periodical cicadas may be a pest in certain years. The immature nymphs live in the soil and feed on tree roots. After thirteen or seventeen years the last-instar nymphs emerge from the soil, become adults, and mate, and the females lay their eggs in tree twigs. When the eggs hatch, the small, antlike nymphs drop to the ground, enter the soil through cracks, and then remain in the soil for thirteen or seventeen years. Damage to turf is because of the emergence holes made by the full-grown nymphs when they leave the soil. As many as 50,000 cicadas may emerge from the soil beneath a large tree.
The European crane fly is found in Canada, the northwestern United States, and New York. The adult looks like a large mosquito, and the immature is called a leatherjacket (Figure 15-1). This is because the larvae have a hard outer skin. The larvae feed on turfgrass roots, crowns, and leaves.
Ticks are not insects because they have eight legs, but they are of great medical importance and turf workers may come into contact with them. The blacklegged tick (Ixodes scapularis), which is also called the deer tick, transmits Lyme disease (Figure 15-33). Lyme disease is the result of a bacterial infection that occurs after the tick has sucked blood from a person. The damage can be quite serious, including arthritis, heart disease, and paralysis.
Even in the adult stage the black-legged tick is only the size of a sesame seed. The nymphs that do most of the disease transmittance are considerably smaller. People generally are unaware of an attached tick unless they examine themselves very carefully. A circular red rash may occur at the site of the bite. Early intervention with antibiotics is almost always successful.
Anyone who finds a small tick on himself should take it to a doctor to have it identified. Lyme disease has been most prevalent in the northeast and mid-Atlantic regions, but it has been found throughout much of the United States.
When weather conditions are favorable for the growth of insect pest populations, injury to turfgrass may occur. If insect populations are large enough to damage a turf area, the turfgrass manager may consider applying an insecticide (Figure 15-34). There are some alternative control measures, but for the present, insecticides are still the primary method of managing serious insect problems. In the future many effective insect control strategies not requiring the use of traditional insecticides will be available to the turfgrass manager.
Insecticides can be a valuable tool if used wisely. Safe handling requires both common sense and following the directions on the label. The turf manager must read and obey all label instructions and precautions. When a turf manager has any questions regarding pesticide use, he or she should contact the Cooperative Extension Service for assistance.
Usually insecticides should not be applied until an insect problem occurs. Unless injury is anticipated, it is a waste of time and money to treat the turf areas. It is also environmentally unsound to apply insecticides unnecessarily.
Until the mid-1970s chlordane, an insecticide belonging to a group of chemicals called chlorinated hydrocarbons, was widely used on turfgrass. It had a lengthy residuality, often killing insects for five years or more after it was applied. However, chlordane and many other chlorinated hydrocarbons persisted for so long that they caused environmental problems, and their use was banned. The insecticides that replaced them, the organophosphates, carbamates, and pyrethroids, are relatively short-lived. Most are usually effective against insects for three to fourteen days.
Until recently the organophosphates and carbamates have dominated the turfgrass insect control market. However, new classes of insecticides are appearing.
The Food Quality Protection Act (FQPA) is legislation passed to ensure the safety of food products and to minimize the exposure of children to pesticides. Some organophosphates and carbamates have been removed from the market to reduce the exposure of Americans to insecticides in these two chemical classes. Though the Act is aimed primarily at pesticide use on vegetables, fruits, and grains, some of the materials that will no longer be available have also been used as turf insecticides.
Pyrethroids are insecticides originally based on the chemistry of pyrethrin, which is found in certain chrysanthemum flowers. The synthetic pyrethoids have a low toxicity to humans but are very toxic to fish.
Imidacloprid (Merit) is an insecticide in a new class, chloronicotinyl. It is effective for several months, has minimal effects on the environment, and is relatively safe to work with. Several other insecticides in this class are also available. The application rates of active ingredient are much lower than those used traditionally with organophosphates and carbamates.
Biorational insecticides are materials that are considered to have fewer adverse effects than traditional insecticides. An example is azadirachtin, derived from the seed of a neem tree, which acts as an insect growth regulator. Some insects that come into contact with it are unable to molt successfully and die. It also acts as a repellent, keeping insects from feeding on treated foliage. It is sometimes called a botanical insecticide.
The most widely used microbial insecticide is Bacillus thuringiensis var. kurstaki. It is a bacterium that produces a toxic protein that damages caterpillars' stomachs. The larvae stop feeding and starve to death. This material works only on caterpillars and is used to control sod webworms and cutworms.
Beauveria bassiana is a fungus that attacks chinch bugs and other insect pests. "Commercial products are avilable."
Entomopathogenic nematodes are tiny roundworms in the genera Steinernema and Heterorhabditis. They enter the bodies of the larvae and release bacteria that kill the insects. Nematodes dry out very quickly so they should be sprayed on moist turf and watered in immediately. Steinernema riobravis (-riobrave) is used to help control mole crickets. Though results with nematodes have been mixed, they offer significant potential for insect control.
Spinosad contains fermentation products produced by the bacterium Saccharopolyspora spinosa. These substances poison the insect but have low human toxicity. Spinosad is primarily used to control caterpillars.
Insecticidal soaps and oils rupture cell membranes in exoskeletons of soft-bodied insects such as aphids. The materials are very safe for the environment and the applicator.
Halofenozide is a type of insect growth regulator that is called a molt-accelerating compound. It causes some grubs and caterpillars to molt too quickly. They die because they molt before they are ready to shed their exoskeleton.
The key to effective insect control is early diagnosis and treatment of problems. Preventing losses to insects requires constant vigilance on the part of the turf manager, who must continually look for insect pests or signs of their presence. Any yellow grass or declining turf must be examined immediately (Figure 15-35). Early detection enables the manager to apply an insecticide before significant turf injury occurs. It is important to remember that the presence of a pest does not mean that significant injury will occur. What will happen depends primarily on how many pests are present. It takes a certain size population to injure the grass.
[FIGURE 15-35 OMITTED]
This is called a threshold and is usually expressed as the number of insects per square foot (0.09 [m.sup.2]). For example, treatment is usually recommended when five to ten white grubs are found per square foot in a moisture-stressed turf. However, the threshold may rise to twenty or more if the turf can be irrigated frequently to compensate for root injury. Threshold population numbers are being compiled for many insect pests.
Insect problems often become serious in the summer because this is when the populations of many species increase in size to injurious levels. Grass is also weakened by heat and drought during summer months and is more likely to succumb to insect injury. A common mistake is to assume that damage resulting from insect feeding is merely summer dormancy caused by hot, dry weather. The symptoms exhibited in both cases may be identical because grass injured by insects experiences moisture stress owing to the loss of fluids, roots, or the disruption of vascular tissue. This misdiagnosis can be avoided by carefully searching the affected turf for insect pests.
Understanding the life cycles of insect pests is essential. This knowledge allows the turf manager to anticipate when problems are likely to occur. Familiarity with life cycles also aids the manager in preparing a spray schedule. Insecticides should be used whenever injury becomes apparent; however, the proper timing of applications helps to ensure effective control. As a general rule, insects are more susceptible to insecticides during their early instars when they are smaller. Susceptibility may decrease as larvae or nymphs mature. Best control often occurs when a treatment is timed to coincide with egg hatching.
There is another advantage to treating the younger immatures. The earlier instars are usually too small to cause extensive damage. The insecticide will not eradicate the entire pest population, but many will be killed. This prevents the majority of the insects from growing large enough to cause serious feeding injury.
The turf manager should be aware that some of the insects will survive an insecticide application. The survivors will not be numerous enough to present an immediate threat to the turf, but when they reproduce the population may build up to injurious levels. The manager should expect and watch for the recurrence of insect problems in the future. Retreatment may eventually become necessary.
To be killed, the insect must come into contact with the insecticide. This contact occurs in several ways. The chemical may be applied directly on the insect. In many cases the pest contacts the insecticide as it moves around in treated grass, thatch, or soil. The insect may also ingest the toxic material if it feeds on tissue covered with or containing insecticide.
Insect pests that live and feed in the soil are the most difficult type to control. It is not possible to apply the insecticide directly to the insect. The chemical must move through the turf and thatch and penetrate the soil to be effective. It takes longer for insecticides to come into contact with soil-inhabiting insects. This can be a problem, especially if the material is tied up in the thatch layer. The shorter-term insecticides may lose much of their toxicity by the time they reach grubs or other soil insects.
The movement of insecticides into the soil is accelerated by applying 0.5 inch (1.3 centimeters) of water after treatment. The water leaches the chemical down to the soil or may help to bring the pest up to the surface. When irrigation is not possible, the turf manager should try to apply the material right before it rains. Sprays should be watered in immediately after application. If irrigation is delayed, the liquid will adhere to the foliage. It may not readily wash off and can be degraded by ultraviolet light. Granular insecticides will not stick to the foliage if the leaves are dry.
Watering before treatment can also be helpful. Insecticides move more readily through the thatch when it is wet. Using large volumes of water when spraying helps to wash liquid materials off the foliage and through the thatch.
Soil inhabitants such as white grubs prefer to feed at the thatch-soil interface. However, if the surface soil is dry they will stay deeper. Most insecticides do not penetrate very deep into the soil. Heavy irrigation before or after treatment will keep the grubs near the surface, where they are most likely to come into contact with the insecticide.
Insects that feed on shoots are easier to control than soil-inhabiting insects. Sprays work very quickly, killing many insects in the first forty-eight hours after application. Treatment in the late afternoon or early evening is ideal because most of the pests that attack the shoots feed at night. An application late in the day ensures maximum contact. The liquid material will either directly contact the insects or dry on and stick to the foliage and the surface of the thatch. Insects that are not killed immediately will come into contact with the insecticide as they move around and feed on the leaves and stems. Sprays directed at shoot-feeding insects are not usually watered in after application because the insecticide would be removed from the target area. Rain should not occur immediately after the application. The turf manager should also avoid mowing the grass for a few days.
The pH of the water used to dissolve or suspend the insecticide can have an impact on the performance of the chemical. Some insecticides have a greatly reduced period of effectiveness when mixed with an alkaline carrier. For example, trichlorfon is stable for over eighty hours in a spray tank with water that has a pH of 6.0, but it loses its ability to kill insects in minutes when the water has a pH of 9.0. Acidifying agents can be added to the water if it has a high pH and the insecticide is sensitive to alkalinity. This information can be found on the pesticide label.
Granular insecticides do not usually kill shoot-feeding insects as quickly as liquid sprays. Granular materials consist of inert carriers such as clay, vermiculite, or corn cob particles that are coated with insecticide. The granules release the insecticide when they absorb moisture. A light irrigation following application hastens the leaching of insecticide from the carrier. Granular materials usually have longer residual activity than sprays because the liquids adhere to the foliage and are broken down by light. Most of the granules fall to the surface of the thatch layer and are less exposed to sunlight. Insects that feed on stems and leaves come into contact with the granular insecticide as they crawl over or through the thatch.
Turf managers must remember to read the label on the insecticide container carefully before using the material. The Cooperative Extension Service or the manufacturer should be consulted if the manager has any questions concerning the proper use of the insecticide.
Well-managed, healthy turfgrass has a better chance of surviving an insect infestation than poorly maintained grass. Strong, vigorous grass plants are more likely to recover from insect damage. Plants that are weak and nonrecuperative are more likely to be severely injured by insect feeding. Proper fertilization, mowing, and watering are an important part of an effective insect control program.
An area of great interest is the development of resistant cultivars. Some varieties presently available contain compounds that are toxic or distasteful to insect pests, but the majority are susceptible to insect injury. In the future resistant varieties will become more common. Some of the perennial ryegrass, fine fescue, and tall fescue cultivars contain endophytes, fungi that live inside the plants. These fungi produce toxic chemicals which discourage feeding by surface-feeding insects. Unfortunately, endophyte levels in the roots are very low, so endophytic varieties are not resistant to insects that feed on roots.
1. The larvae of beetle species that live in the soil and feed on turfgrass roots are called --.
2. The period between molts is referred to as an --.
3. Turfgrass insect pests have two types of mouthparts--chewing and --.
4. The -- is the immature stage of the lawn moth.
5. Insects that secrete a waxy protective covering are called --.
6. The greenbug is actually an --.
7. Chinch bug injury is often mistaken for --.
8. How many grass species serve as the food source for the annual bluegrass weevil?
9. The larva of a frit fly is called a --.
10. -- have eight legs and are closely related to insects.
11. The front legs of mole crickets are adapted for --.
12. Before using an insecticide, the turf manager must read the --.
13. An insecticide that is directed against soil insects should be -- after it has been applied.
14. A turf manager attempting to control shoot-feeding insects should not -- the grass for a few days following an insecticide application.
15. Discuss why an insecticide application might fail to result in satisfactory control of an insect pest.
16. Discuss the significance of thresholds.
17. Why are white grubs sometimes harder to control than chinch bugs?
18. The insect that lives inside a cyst attached to the roots is called a --.
19. The vector of Lyme disease, formerly called the deer tick, is now called the -- tick.
20. The leatherjacket is the immature stage of a --.
Figure 15-34 Common and trade names of pesticides used to control insect and mite pests on turfgrass in 2006. COMMON NAME TRADE NAME Acephate Acephate Azadirachtin Azatin, BioNeem Bacillus thuringiensis Dipel kurstaki Beauveria bassiana Naturalis Bifenthrin Talstar Carbaryl Sevin and many others Chlorpyrifos Dursban and many others Clothianidin Arena Cyfluthrin Tempo Cypermethrin Cynoff Demon Deltamethrin Deltagard Diazinon Diazinon Dicofol Kelthane Ethion Ethion Ethoprop Mocap Fenamiphos Nemacur Fenoxycarb Award Fipronil Ceasefire, Chipco Choice Halofenozide Mach 2 Heterorhabditis Cruiser bacteriophora Hydramethylnon Amdro Siege Imidacloprid Merit Lambda-cyhalothrin Battle Scimitar Malathion Malathion Myrothecium DiTera-T verrucaria Paenibacillus Milky spore popilliae powder Permethrin Astro, Flee, and others Potassium salts of M-Pede fatty acids Pyrethrin Exciter Steinernema Nematec scapterisci Spinosad Conserve SC Tau-fluvalinate Mavrik Trichlorfon Dylox
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|Author:||Emmons, Robert D.|
|Publication:||Turfgrass Science and Management, 4th ed.|
|Date:||Jan 1, 2008|
|Previous Article:||Chapter 14 Weeds.|
|Next Article:||Chapter 16 Turfgrass diseases.|