Controlling insects in warm-season turfgrass
At one time, turf managers used highly toxic materials such as nicotine and cyanide for controlling pests in southern turf. Today's turf managers can choose from many safer and more effective control methods. This is fortunate, because insect pests seem to be more numerous and are moving into new territories. The red imported fire ant as well as imported mole cricket species are among the most serious turf insects today but were not even mentioned in Enlow and Stokes' 1929 publication, Lawns in Florida. In addition, today's customers have higher expectations and lower tolerance for damage. Thus, turf managers, especially those in the South, face greater pest-control challenges than their predecessors.
Integrated pest management You can best manage turfgrass pests, like most other pests, with an integrated program. Growing healthy turf is the first step in preventing pest outbreaks or reducing the stress they cause. Prudent mowing, fertilizing and irrigating encourage stress tolerance and recovery from pest damage.
Research has shown that applications of high rates of nitrogen can trigger outbreaks of fast-reproducing species such as caterpillars and chinch bugs. It seems that succulent turf growth is as attractive to pests as it is to people. Therefore, you should use slow-release sources or frequent, light fertilizer applications. Further, irrigate conservatively to replace the water actually used through evapotranspiration.
One of the most important components of a pest-management program is monitoring. In addition to detecting a pest problem, monitoring helps you keep track of pest populations over time. Early detection helps you keep small outbreaks from getting larger, and frequent inspection allows the opportunity to better time your control measures. Scout frequently--once a week--and keep careful records of pest- and beneficial-insect populations. Become familiar with the turf area you are trying to protect and you will soon learn where problems might first appear.
Several natural enemies of turf pests already are established in the Southeastern United States. The striped earwig is a fearsome-looking insect and a good predator of caterpillars. Along with the big-eyed bug, it has an appetite for chinch bug eggs. General predators such as ground beetles also are effective at reducing populations of some pests. When you have the option, use selective insecticides that will leave the beneficials in place. For example, spinosad and Bacillus thuringiensis toxins are highly effective against caterpillar pests (such as webworms and armyworms). Using such selective products allows you to control the target pest without eliminating predators that may be keeping some other pest in check.
The prominent insect pests of warm-season turf fall into five main groups: mole crickets, chinch bugs, ants, grubs and caterpillars (see "Important pests of Southern turf," page 42). Let's look at some specific information about each of these groups.
Mole crickets Mole crickets cause extensive damage to turf, affecting primarily bermudagrass and bahiagrass but occasionally other turf species too. Mole crickets are burrowing insects and their digging can uproot turf, exposing roots to drying and ruining smooth playing surfaces. The tawny and short-winged mole crickets actively feed on turf roots, while the Southern mole cricket is a predator of other insects. However, they all damage turf with their tunneling. Mole crickets lay their eggs in tunnels in spring and summer, and the eggs hatch within 1 month. Spring flights of the adults can quickly spread the infestation to adjacent areas and hamper control.
Mole crickets leave an obvious sign: tunneling. If you see tunneling, sample from the affected area by soaking a 4-square-foot area with a soapy-water solution (2 gallons of water with 1 to 2 ounces of detergent or dish soap). The solution agitates mole crickets, which come to the soil surface where you can easily count them. If you find more than one or two mole crickets per square foot, it is time to take action.
Chemical control of mole crickets is most effective when you target sprays or granular formulations at the nymphal stages, usually between late May and early July. Late-season applications are possible, but the increasing size of the mole crickets at that time reduces insecticide efficacy. A number of products are labeled for mole-cricket management (see "Insecticide options for Southern turf," at left). Apply sprays and granules when the turf is moist and water them in with about 0.5 inch of irrigation. Scatter-baits containing chlorpyrifos or carbaryl also are effective. Apply baits evenly and lightly over infested areas in the late afternoon on days when rain is not expected. Do not water-in baits.
One of the most successful examples of introduced biological control is the Florida program against mole crickets. University scientists recently introduced the Brazilian red-eyed fly, Ormia depleta, a natural enemy of tawny and Southern mole crickets. It now has spread to 38 Florida counties. According to Dr. Howard Frank, University of Florida, the fly is unlikely to spread farther north because of its subtropical origin and its need for a year-round nectar source.
The various species of the nematode Steinernema, developed both at the University of Florida and elsewhere, are effective biopesticides against mole crickets. Because of their multiple-season suppression of mole crickets, nematodes are potentially very cost effective. You can apply them with conventional spray equipment. However, because they are living organisms, adequate moisture must be present at the time of application. Due to this and other limitations, you cannot rely on Steinernema exclusively for mole cricket control. Many golf-course superintendents apply acephate or ethoprop, but as the table at left shows, numerous effective controls are available. Fipronil, Rhone Poulenc's Chipco Choice, is a new product with good activity against mole crickets.
Grubs Another important group of below-ground feeders are the white grubs--a group of related species of scarab beetles that includes chafers and June beetles, among many others. The "C"-shaped grub larvae mature to a length of about 0.5 to 2 inches, depending on the species, and are white to tannish in color with brown head capsules.
White-grub life cycles vary depending on geographic location and the grub species. As a general rule, larvae feed through the summer and fall, overwinter in deeper soil and then migrate upwards to feed on grass roots near the soil surface in the spring. Then they pupate a few inches below the soil surface, and the adults emerge in late spring to early summer, when they mate and lay eggs. This next generation hatches, beginning the cycle again. Most species share this general pattern, though many spend 2 or more years in the larval stage before finally pupating in their final spring. Regardless, grubs are larger in late summer and early fall than they are earlier in the year. Thus, grub damage typically becomes apparent at this time of the year. Drought and heat during this time often place additional stress, compounding the damage.
Early identification of white-grub damage can be difficult. Signs include: * Wilted grass that does not respond to irrigation and fertilization * Thin turf with poor knitting *Turf that pulls up in your hands when you tug on it.
If these conditions exist, suspect below-ground white-grub activity and investigate further. Roll back a 1-square-foot patch of turf and inspect for grubs and signs of feeding (chewed off roots). Sample at several locations near visible damage. Concentrations of three to four grubs per square foot call for control measures. White-grub insecticides need to penetrate into the soil, where the grubs live. Therefore, it's important to irrigate after an application to move the chemical into the soil. In addition to numerous traditional products that still are widely used, manufacturers have introduced several new insecticides within the last few years that show outstanding qualities. Notable among them are halofenozide (RohMid's Mach 2) and imidacloprid (Bayer's Merit). See the table on page 36 for other control options.
Chinch bugs Depending on the location, one to several generations of chinch bugs occur in a year. The Southern chinch bug feeds mainly on St. Augustinegrass by sucking fluid from stolons. Its eggs hatch into bright-red nymphs with white bands across their backs. Nymphs molt five times--becoming adults after the last molt--all within as little as 5 weeks. Adults are slate black with silvery-white wings and about one-fifth of an inch long.
Chinch-bug activity often starts during the drier part of the year in many southern areas. Chinch-bug-induced stress typically shows first in water-stressed areas such as along sidewalks or in poorly irrigated spots. Therefore, irrigation systems that are not delivering adequate water to some or all of the turf exacerbate the problem. Symptoms of feeding include patches of yellowish to brownish turf.
Because the same symptoms can occur due to other problems, such as water stress or disease, it is wise to inspect for signs of the insects in areas adjacent to the damage. If you find no chinch bugs, the damage you're seeing may be the result of some other factor. When scouting, examine the soil surface and leaves for crawling chinch bugs. Another good method of monitoring for chinch bugs is to push a coffee can (with both ends cut out) an inch or so into the soil, and fill it with water. Chinch bugs float to the top within a few minutes. You'll need to monitor for chinch bugs throughout the growing season.
As another aid to help you confirm a chinch-bug problem, look for predatory insects. The most common chinch-bug predator is the black big-eyed bug, an insect that looks similar to its prey. In addition, the striped-earwig is an important predator of chinch bugs in all stages of development.
When damage is readily apparent or when counts reach 15 to 20 chinch bugs per square foot, pesticide application is necessary. Numerous products are available (see the table on page 36). Spot treatments are an option when infestations are not too widespread. However, be sure to apply the insecticide to the damaged area plus a 5-foot buffer.
The problem of organophosphate-resistant chinch bugs (which have developed in some Southern areas) illustrates the importance of rotating with insecticides among different chemical families. This slows the buildup of resistant populations. However, be sure you've performed all aspects of the application properly before you blame resistance for poor control--many factors during the loading, mixing and application process can reduce efficacy.
'Floratam' St. Augustinegrass was released in 1973 for its resistance to chinch bugs. 'Floratam' was immune from economic damage until 1985, when a virulent population of chinch bug was discovered and reported from most counties in Florida. Although 'Floratam' is less often attacked by chinch bugs than most other varieties, regular monitoring is still necessary.
Fire ants Pests introduced to the United States from other parts of the world are freed of their natural enemies. Thus, they often are more of a nuisance here than in their native range. An example is the red imported fire ant, Solenopsis invicta. In South America, parasites--including a small hump-backed fly--attack the Solenopsis fire ant. Here in the Southern United States, however, fire ants have spread unabated since their introduction. Therefore, scientists have imported the parasitic fly and plan to release it to control the imported ant.
In the meantime, insecticide baits and contacts (see the table on page 36) are useful for control of imported fire ants. In the case of baits (carbaryl, chlorpyrifos, fenoxycarb and hydramethylnon are available as baits) the ants carry the bait particles into their mound, where workers eventually feed it to the queen. Depending on the bait product, it will either kill the queen directly or prevent the queen from producting worker ants that nourish and protect the queen, leading to her death. The effectiveness of baits is greatest when you apply the products in the late afternoon and evening, both because the aboveground activity period of the insect is greatest, and because product breakdown by ultraviolet light is reduced. Fire ants are most active when soil is 60 degrees F or warmer, and bait treatments will be most effective during such times. Do not apply baits before a rain or irrigation.
Control strategies for fire ants do not rely so much on systematic monitoring or treatment thresholds--depending on the site, there may be zero tolerance for fire ants. In such cases, each mound may be treated individually, though broadcast treatments may be more efficient for larger infested areas. The mounds are conspicuous in most landscapes, which is one reason they demand control measures. However, due to their size, they also can disrupt equipment in addition to affecting appearance. Worst of all, the ants' stings can be quite dangerous to humans and animals.
Caterpillars Several types of caterpillars affect Southern turf. One of the most significant groups is the sod webworms, which include several species of moths whose larvae inhabit and feed on turfgrasses. The moths are small, light-colored insects that frequently are visible as they fly over lawns in a zigzag pattern during evening hours. At rest, the small moths have a distinctive tubular shape.
Sod webworms vary in appearance, depending on species, but most are gray-green with obvious spots and a dark-brown head. They attain 0.75 to 1.0 inch in length when fully grown and construct silk-lined burrows in thatch, from which they emerge at night to feed on grass leaves. Feeding damage starts as small, irregular patches of dead or dying turf that grow larger as the webworms continue feeding. Other symptoms to look for include frass (webworm excrement) and small holes in the turf caused by birds feeding on the webworms.
The first adult moths of the year emerge in late spring or early summer and lay their eggs soon thereafter. This first generation of offspring is usually too sparse to cause visible damage, but subsequent generations (several occur each year) tend to be greater in number. Thus, webworm damage increases as summer progresses. To monitor for webworms, use a soap flush or a mild pyrethrin solution (about 1 tablespoon of 2-percent pyrethrin per gallon of water) to force the webworms from their burrows. Treatment thresholds vary according to how much visible damage you or your client can tolerate. Infestations of 6 or more caterpillars per square foot cause visible damage.
Chlorpyrifos is a common treatment for webworms, but several good alternatives are available, including two new products: spinosad (Dow's Conserve) and halofenozide (RohMid's Mach 2). Turf managers also should consider one of the Bacillus thuringiensis products, which are selective against caterpillars. See the table on page 36 for other treatment options.
Dr. Phil Busey is associate professor of environmental horticulture, and Dr. Tom Weissling is assistant professor of entomology and nematology, both at the University of Florida (Fort Lauderdale).
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