Common Pests

The larval stage of several insects cause damage to home lawns. The larvae feed on roots and underground stems of grass. A thick, healthy lawn may not be resistant to insects, but will be better able to recover from injury and will be able to tolerate some damage without it being noticeable.

If you suspect insect injury, look closely in the thatch layer and top 1-2 inches of soil for larvae. Make sure you have correctly identified the insect and understand its lifecycle to determine the best course of action for control.

Billbugs are perhaps the most common insect affecting home lawns in Idaho. The adults, which are about 1/4 inch long, can be seen in the spring, walking along sidewalks especially on the southern sides of buildings.

The adults are a black weevil, have a long snout and will play dead when disturbed. The adults do very little damage, but in the larval stage billbugs eat grass stems and roots. Adults become active when soil temperatures reach 55º F, usually early to mid-May. The larvae are small (1/8-1/4 inch long), white, legless grubs with a brown head.

Lawns damaged by billbugs look like they are drought stressed because the grass blades are basically severed from the roots. Grass blades can be easily pulled out by hand with a light tug. A healthy, vigorously growing lawn will recover from moderate billbug damage and symptoms may go unnoticed. However, under-fertilized lawns or lawns that are otherwise stressed will be more susceptible to billbug damage.

Control. If you have areas with known billbug problems, control measures should be targeted against the adults in the spring when they are active and seen crawling along sidewalks or other exposed areas. Waiting until damage is visible may be too late since the damage has already been done. If targeting larvae, good coverage and movement of the insecticide past the thatch layer are very important. Since adults are on the surface of the turf, they are more easily contacted with insecticides.

White grubs are the larval stage of a beetle known as scarab beetles or more commonly as May/June beetles and masked chafers. White grubs have a characteristic “C” shape, are creamy white, with three pairs of legs and grow to a size of up to 1 to 1 1/4 inches long.

White grubs feed on grass roots causing severe wilting and eventually death of affected lawns. The sod will tend to lift away when pulled, but grass blades will generally stay intact since the grubs have mainly eaten roots. Additionally, skunks and raccoons in search of larvae will cause considerable damage as a result of their digging and feeding on grubs.

Grubs are generally found in the top inch or so of the soil and will go much deeper during the winter months. Masked chafer grubs have a one-year life cycle overwintering as larvae with the adults emerging in mid to late June.

The May/June beetles on the other hand have a three-year life cycle with adults emerging in May and June, laying eggs and the larvae feeding during the summer and overwintering. The second year, when most of the damage occurs, the grubs feed throughout the summer. In the third year, the grubs complete their development in the spring and early summer forming pupae and adults the following year to start the cycle again.

Control. Many insecticides are labeled for white grub control, however, it is very difficult to control white grubs because of the difficulty of getting the chemical into the soil where they are active. Excessive thatch can impede the movement of the chemical into the root zone where grubs are feeding. Core aeration can help increase the effectiveness of insecticide applications. Proper watering will also help, but it is important not to ove- water. Over-watering can actually decrease the effectiveness of insecticides.

Find additional information on billbugs and white grubs at Colorado State University.

Earthworms and night crawlers are the main cause of bumpy lawns, a common complaint of many homeowners. Worms leave castings or small mounds of soil on the soil surface. These mounds soon dry and harden causing an uneven surface, which can be somewhat bothersome during mowing operations. It is important to remember that the benefits of earthworms far outweigh the nuisance caused by these castings. Earthworms help decompose thatch, improve water and air movement and soil structure for good root growth. Earthworms are indeed a good indicator of a fertile soil.

Extremely bumpy lawns may also indicate other problems such as a thin turf stand due to a poor fertilization program. Following good fertility and watering guidelines will keep a lawn growing vigorously and will make bumps less noticeable.

In severely bumpy lawns, rolling in conjunction with aerifying may help reduce the problem, but generally, lawn rolling is not advised since it can lead to soil compaction.

Home lawns in southern Idaho are generally not faced with many disease problems because of the dry climate. Improper fertility or irrigation practices are generally the main cause of disease problems. Cool, overcast weather conditions or areas in a lawn with excessive shade also can contribute to disease outbreaks. Generally, however, a properly managed lawn will be resistant to severe disease outbreaks.

Powdery mildew

Shady areas with Kentucky bluegrass are especially susceptible to powdery mildew. Powdery mildew appears as a white, powdery mass on grass blades and large affected areas appear as if they have been dusted with flour or talcum powder. It is favored by cool, humid, shady conditions and may even appear after cloudy weather. Poor air circulation and heavy fertilization worsen the problem.

Control. If trees are causing the shade and if possible, trim trees to minimize shade and improve air circulation. Powdery mildew is rarely serious enough to warrant control with fungicides. Overseed shady areas with shade tolerant grasses such as fine fescues or tall fescue.

Additional close up pictures and disease descriptions can be found at www.ipm.iastate.edu/

Rust

Rust is an orange colored fungus that affects the grass blades. Heavily infested lawns will leave a rust-colored dust on shoes and clothing. Rust is usually a result of under fertilized and/or drought stressed turf, and the disease is favored by cloudy, overcast conditions. Light, frequent watering will keep leaf blades wet and also increase the development of rust.

Control. Generally, good fertilization and watering practices will prevent rust from occurring. Preventative fungicides are available, but generally not warranted for home lawns.

Fairy ring

Dark circles or partial circles of lush green grass in a lawn are caused by mushroom type fungi living in the soil. These dark circles of grass are commonly referred to as fairy rings. Sometimes mushrooms will appear following wet, humid weather. In severe cases, a ring of dead grass will appear inside the ring of green grass.

The fungus that causes fairy ring grows on organic matter buried in the soil. As the fungus breaks down organic matter, nitrogen is released causing the green lush growth. In some cases, the growth of the fungus is so thick in the soil that water cannot penetrate, causing the grass to become drought stressed and die.

Control. Prevention of fairy ring involves removal of tree stumps and other wood materials from a lawn site prior to establishment. If fairy ring still appears, it can be very difficult to remove the fungus entirely. Core aeration and hand watering the affected area will help move water into the affected soil and help introduce other microorganisms that will compete with the fungus. Make sure to clean aeration equipment to avoid introducing the fungus to other areas of the lawn. Proper fertility and watering practices will help reduce the severity of the symptoms and in some cases prevent fairy ring from developing. Fungicide drenches have shown irregular success and are generally not recommended for home lawns. Severe fairy rings with large areas of dead grass may warrant removal of grass and soil from the rings followed by introducing new soil and re-seeding the area.

Most weed problems in lawns are associated with a weak, thin turf. A thin turf is easily pushed aside by aggressive weeds which can become worse over time. Make sure to follow good fertilization, irrigation and mowing guidelines to build a thick, vigorously growing lawn. Heavy weed populations are usually an indication of some other inherent problem with the lawn.

Some perennial weeds, like white clover, can still become problems even in well managed lawns. Many herbicides are available to effectively control weeds in lawns, but their success largely depends on proper application, and perhaps more importantly, on correct timing. Knowing what weeds you have will help you determine the best time of the year to control them.

Realize that it is impossible to eradicate all weeds from a lawn even with herbicide use. Learn to tolerate some weeds in your lawn and avoid indiscriminate use of herbicides which can injure trees, surrounding landscape plants and even the lawn itself.

Photographs of many weeds can be found at WSSA’s Photo Gallery.

Perennial Broadleaf Weeds

Some common perennial broadleaf weeds in home lawns include dandelion, field bindweed (also called morningglory), white clover, curly dock, ground ivy, Canada thistle, broadleaf plantain, buckhorn plantain and yarrow. Make sure to properly identify the weeds before choosing herbicides for control. University of Idaho extension educators, master gardeners and nursery personnel can help you with correct identification.

Broadleaf weeds can be controlled with postemergence herbicides (a chemical that is applied to weeds after the weeds have emerged from the soil) which kill weeds that are actively growing. Postemergence herbicides do not prevent weeds from germinating.

The best time of the year to control perennial weeds is in late summer or early fall when the weeds are preparing for winter. In preparation for winter, perennial weeds move energy reserves from the leaves to underground stems and roots, so a herbicide application at this time will ensure movement of the herbicide to these plant parts, thus resulting in a more effective kill because the roots are being affected. Spring applications to perennial weeds can slow their growth and may kill them, but it is more difficult. Regardless of when applications are made, make sure the weeds are actively growing at time of application. Avoid mowing for 1 to 2 days before and after the application to ensure maximum uptake of the herbicide by the weeds.

There are many broadleaf weed control products available for home use. These products will contain one or a combination of the following chemicals: 2,4-D, 2,4-DP, MCPP, MCPA and dicamba. They are safe to use on cool-season lawn grasses. Liquid and granular formulations of these chemicals are available. It is very important to properly calibrate sprayers or granular spreaders to ensure accurate, uniform application and avoid spraying adjacent flower beds or susceptible plants. Be sure to read and follow all label directions.

Perennial Grassy Weeds

Perennial grassy weeds are the most difficult weeds to control in a home lawn. Some common perennial grassy weeds include quackgrass, roughstalk bluegrass, smooth bromegrass, annual bluegrass (there exist some perennial biotypes) and even other cool-season grasses such as tall fescue and creeping bentgrass. There are essentially no herbicides available for the selective control of these weeds in a lawn. Removal of these problem weedy grasses prior to establishing a lawn and the use of high quality seed or sod is essential to preventing these weeds from becoming a problem. Many home lawns are established with poor quality seed that has high amounts of weeds such as annual bluegrass and roughstalk bluegrass. What is contained in a seed lot you are considering to purchase is readily available on the seed label, but most homeowners are unaware of its importance. If small patches of perennial grasses are found in a lawn, physical removal with a shovel or spraying with a non-selective herbicide such as glyphosate is the only option followed by re-seeding or sodding the bare areas.

Annual Grassy Weeds

Weeds like crabgrass and foxtail are warm-season grasses that germinate from seed in the spring and infest lawns during the hot days of summer. They tend to invade lawns along sidewalks and driveways where temperatures are hottest and lawns are thin. Thick, vigorously growing lawns will out-compete most annual grassy weeds.

Annual grassy weeds are best controlled with pre-emergence herbicides (a chemical that is applied before the seeds have germinated) which kill germinating weeds. These herbicides must be applied well before the weeds germinate since they will not kill weeds once they have emerged. Additionally, some of these pre-emergence herbicides are impregnated on fertilizer granules and applied as a weed and feed. Crabgrass will germinate when soil temperatures reach 55 to 60º F. This occurs around mid-March to early April for the Treasure Valley, Magic Valley and northern Idaho and late March to mid-April for central and eastern Idaho.

There are some herbicides that will kill young annual grassy weeds, but they usually only work well on very young plants so application timing is critical.

Do not overseed into areas that have recently been treated with pre-emergence herbicides because the chemical will kill emerging lawn grasses as well. Check the label of the herbicide to see how long you need to wait before planting into an area treated with a pre-emergence herbicide.