Here are some of the more common lawn insects that can be very harmful and troublesome.

Clover and Other Mites of Turf grass

by W.S. Cranshaw ¹

Quick Facts...

• Several species of spider mites can damage turfgrass in Colorado: clover mite, Banks grass mite and brown wheat mite.
• Most damage occurs during early to midspring.
• Damage to turfgrass is primarily related to dry conditions and turfgrass stressed by drought.
• Clover mites can be a serious nuisance pest when they enter buildings in spring.

Many species of mites are common in Colorado turfgrass. Some, such as the oribatid or "hardshell" mites, are important in the breakdown of thatch and the recycling of nutrients. Other are important predators of pest insects and mites. Three spider mites species are among those that damage Colorado turf: clover mites, Banks grass mites and brown wheat mites.

Clover Mites

Figure 1. Clover mite with egg.

Clover mites (Bryobia praetiosa) are a common type of spider mite in Colorado. They breed outdoors on turfgrass, clover and other plants during spring and fall. During October and November, clover mites seek protected areas to overwinter and may move into homes in large numbers. This also occurs from late February through early May. They are a common indoor nuisance problem at either time.

Clover mites are smaller than the head of a pin and range in color from reddish or brown to dark green. Under close examination they have an unusually long pair of front legs, which distinguishes them from the common spider mites found on garden plants.

Clover mites are most often encountered as nuisance pests in homes. During warm days in fall and spring, large numbers of clover mites may become active and enter homes through cracks around windows and doors. South-facing walls usually are more heavily infested. The crawling mites may spread to walls, curtains, furniture and carpet. Typically, clover mites are described as "walking dust specks." Although they do not bite people, transmit diseases or feed on household furnishings, they can be a serious nuisance. When crushed, clover mites leave rusty red stains that are noticeable on white surfaces.

During early to midspring, clover mites also may damage turfgrass around building foundations and in other warm, dry areas of a lawn. Feeding damage appears as small, meandering silver streaks in the leaves. When mite populations are high, leaves may be extensively injured and die. Areas of grass extending several feet from the building foundation may be totally killed, appearing as light brown, irregular dead patches.

Figure 2. Clover mites on sticky card.

Clover mite injury to turf is commonly mistaken for winter kill and usually is found in the same sunny, dry areas of the lawn where winter drying problems occur. Furthermore, almost all injury occurs within 10 feet of a building, tree or some other upright surface. This is because clover mites periodically climb out of a lawn to shed their old skins and lay eggs.

Clover mites produce two or more outdoor generations during the cooler seasons, feeding on grasses and other plants. However, turfgrass injury occurs only early in the growing season, from February to May. As temperatures warm in late spring, clover mites produce dormant eggs that do not hatch until the return of freezing temperatures in fall. Because of this habit, clover mites are considered cool-season mites, in contrast to many other spider mites that cause greatest damage during warm months.

 

 

Banks Grass Mite

Figure 3. Banks grass mite. (Photo by F. Peairs.)

Figure 4. Banks grass mite turn injury.

Banks grass mite (Oligonychus pratensis) is a common mite species in Colorado. It is a serious pest of corn and also damages drought-stressed turf. It causes grass to turn a bleached straw color, often killing it rapidly. The Banks grass mite adapts more to warm weather than the other common turf damaging mites and is found throughout most of the growing season.

Banks grass mite differs considerably in appearance from the other turf-damaging mites. It is smaller and lighter in color. During most of the season, it is green; the young stages are a paler color. During periods when the mites run out of food or environmental conditions are unfavorable, they may temporarily turn bright red. This mite lacks the elongated front pair of legs of the clover mite. It is related to the spruce spider mite (Oligonychus ununguis), a common pest of evergreens but with different feeding habits.

Banks grass mite is more destructive to turf than other turfgrass mites. In early stages of feeding injury, there is small, white flecking (stippling) similar to that of other mites. A slight purpling of the injured grass blade may be observed, which also is associated with brown wheat mite injury. Dead grass takes on a brownish-yellow color and the blades are stiff. Under favorable conditions, severe injury can progress rapidly. Almost all serious injury by Banks grass mite is related to drought stress.

Banks grass mites spend much of the time feeding and resting at the base of the grass plant. This makes them somewhat difficult to detect and inhibits effective control.

 

 

Billbugs and White Grubs

by W.S. Cranshaw and R. Zimmerman ¹

Quick Facts...

• Billbugs and white grubs are insects that damage turf grasses by feeding on the roots.
• Heavy infestations of billbugs and white grubs may kill grass or attract mammals, such as skunks, that damage grass when feeding on grubs.
• Healthy lawns tolerate injury better than lawns in poor condition.
• Time insecticide applications for when billbug adults are present.
• White grubs are best controlled when a maximum number of young grubs are present in the upper root zone.

Billbugs and white grubs are serious pests of turfgrass in parts of Colorado. Both groups of insects feed below ground and damage roots or the growing crown area of the plant. Infestations also may attract predators, such as skunks and raccoons, that dig and damage lawns in search of the insects.

Billbugs

Figure 1: Denver billbug adult.

Figure 2: Denver billbug larvae.

Billbugs are a type of weevil or "snout beetle." Adult weevils can be seen crossing sidewalks and driveways during late summer or spring. In spring and summer, adults cause minor injuries to grasses as the females cut small holes in the stems of plants and insert their eggs.

The young billbug "grubs" are the primary damaging stage. Billbug grubs are legless, generally white or cream, with a brown head. They may reach 1/3 to 1/2 inch long when full-grown. Young grubs feed within the crown area of the plant and kill it. The stems of infested plants are easily detached at the soil surface. The ends appear sawed-off, often with a sawdust-like material present. Older billbug larvae feed in the lower crown and plant root zone. Small piles of light sawdust-like material are produced during feeding.

Billbug injury is most common on new lawns, particularly those established with sod. Within lawns, most damage occurs near evergreen shrubbery or other protective sites. Billbug injury appears as wilting and occasional death of grass, often in small scattered patches. Extensive areas of a lawn may be killed during severe infestations.

Bluegrass Billbug

At least two species of billbugs may be found in Colorado lawns. The bluegrass billbug (Sphenophorous parvulus) overwinters as an adult in protected areas, such as under debris near building foundations or at the interface of turf and sidewalk. Eggs are produced and laid in late May, June and early July. Larvae develop over the course of several months. Peak larval injury occurs in late June and July. When full-grown, the larvae pupate a few inches deep in the soil. The adults emerge in two to three weeks, feed briefly and seek overwintering shelter. There is one generation per year.

Denver Billbug

The Denver billbug (Sphenophorous cicastriatus) is far more common throughout Colorado. The life cycle of this insect is more complicated than the bluegrass billbug. Some of the insects overwinter as adults, but most remain in the larval stage and feed throughout spring. Egg-laying occurs throughout most of the growing season, peaking in June and July.

Billbug Control

Different varieties of bluegrass exhibit a range in resistance to bluegrass billbug. The common varieties tend to be more resistant. Billbug resistance also occurs in many perennial ryegrass cultivars, particularly those that contain endophytic fungi.

Biological controls include predation by birds and hunting wasps, fungal diseases and parasites. Also, insect parasitic nematodes (Steinernema species, Heterorhabditis species) are effective against both larvae and adult stages and may be used as a biological control. The nematodes are available from many mail order suppliers and several nurseries.

Controlling billbugs with insecticides is difficult when they are in the larval (grub) stage. Young larvae are protected within the plant. Older larvae occur in the root zone where insecticides fail to penetrate.

Best control for the bluegrass billbug occurs when sprays are applied in early May to kill adult insects prior to egg laying. Current information on the Denver billbug indicates that a slightly later timing, in early June, is more appropriate. Apply adult sprays so insecticide residues remain as long as possible on foliage and in the crown area of the plant. This may be achieved better with liquid sprays than with granular formulations.

White Grubs

Figure 3: White grub larva.

White grubs are the most damaging insects in Colorado lawns along the Western Slope, in the Arkansas Valley, and through much of the Eastern Plains. The larval or grub stage feeds on grass roots. Severe feeding injuries result in wilting and often death of infested areas. Because white grubs also are a favorite food of skunks and raccoons, damage by these mammals in search of food may exceed that caused by white grubs.

White grubs live in the soil, often in the top inch of the root zone during warm months. They generally are creamy white with three pairs of legs. They typically curve their bodies into a distinctive C-shape. Grubs of the larger Colorado species may reach 1 to 1 1/2 inches long.

Grubs move down deep in the soil and remain below the frost line during winter. Adult stages of white grubs are known as scarab beetles. May beetles, June beetles, chafers and dung beetles are other scarab species found in the state. Most scarab beetles in Colorado are beneficial and help recycle nutrients in organic matter, such as dung. A few species, however, are important turf pests.

Figure 4: Life cycle of an annual white grub (chafer).

Masked Chafers (Cyclocephala spp.)

These are white grubs that commonly damage turf in the Pueblo and Western Slope areas. Sometimes known as annual white grubs, masked chafers require only one year to complete their life cycle (Figure 4). Flights of egg-laying adult beetles occur in June and continue for about one and a half months.

Larvae feed on grass roots for several months. Peak injury occurs in late summer and early fall. They overwinter in the soil, below the frost line, and resume feeding in spring. Favorable growing conditions in spring usually allow grass to outgrow visible damage during that time. On drought-stressed turf, populations of nine or more grubs per square foot can produce visible injury. Higher grub populations can be tolerated on more vigorously growing turfgrass.

Figure 5: Life cycle of May/June beetle white grubs.

May and June beetles (Phyllophaga spp., Polyphylla spp.)

These are the largest of the white grubs. Most injury by these insects occurs along the Eastern Plains, particularly in the southeast area of the state.

Most May and June beetles have a three-year life cycle (Figure 5). Adult beetles emerge during May and June and lay eggs in the soil. Grubs feed during the summer and move deep in the soil to overwinter. Grubs return to the root zone and feed throughout the following summer. May and June beetle grubs cause most injury during this second season of their life cycle. During spring and early summer of the next year, the grubs complete development, cease feeding, and turn into pupae and adults that remain inactive in the soil. Adult beetles emerge next season. Because of their large size, lawn injury by May or June beetle grubs can occur from populations of five or fewer grubs per square foot.

Problems can result from a rarely seen small species of white grub, the black turfgrass ataenius (Ataenius spretulus). Damage by this species is confined to annual bluegrass, which is a common weed grass in lawns. Large infestations, of several dozen grubs per square foot, may be needed to cause visible injury. The small, black adult beetles are often seen flying at dusk during midspring and again in early summer.