Lawn Management & Problems

Lawn Problems
Adapted from Gail Schumann and Richard Cooper, University of Massachusetts Cooperative Extension Service, 2006

Lawn problems can occur in small areas or larger patches, or entire lawns can die. Sometimes the problems are due to poor growing conditions, improper lawn care practices, or extreme weather conditions. The following is a guide to help you decide what conditions may be causing problems in your lawn. Then you can follow the links for more detailed information.

After Winter but Before Spring Green-Up

Sign/Symptom	Cause	Prevention/Treatment
Large areas of straw-colored grass, especially where exposed to wind with little snow cover.	Winter desiccation
New leaves killed back	Spring frost damage
White, pink, and gray mold in circular patches on moist grass	Snow molds	In Spring: Rake away dead grass. In Fall and Winter: - Avoid snow molds by mowing until grass stops growing in the fall. - Avoid fall nitrogen applications as they will delay dormancy. - Prevent deep piling of snow along walks and driveways where there is grass.
Dead or yellowed grass along sidewalks, driveways, or roads where salt has been applied	Salt damage	- Water heavily to try to wash away salt - Reseed where the lawn is thin. - Avoid salt when possible; try sand, cat litter, environmentally-safe deicing chemicals, etc. as a substitute for salt.

 After Spring Green-Up
Soil
Compaction
- Aerate the soil.
- Add organic matter during lawn reconstruction.
- Reroute foot traffic and play areas to avoid frequent packing down of soil.
pH
- Have soil pH tested and adjust pH as recommended.
Low Nutrient Levels (yellowed, slow-growing lawn)
- A balanced fertilizer of nitrogen/phosphorus/potassium promotes a healthy lawn.
- Have soil pH tested and adjust pH as recommended.
Improper Fertilizer Application
- The wrong amount of fertilizer can result when the spreader is not calibrated properly. Take special care when changing directions while spreading. Brown streaks lined with extra green growth can occur in areas of application overlap. Yellow, nutrient-deficient streaks may occur in missed areas.
Dog Urine (Spots of brown grass, perhaps with green area around them.)
Chemical Damage
- Many household chemicals, salt, oil, gasoline, concentrated fertilizers, herbicides, and gas leaks can cause sudden scorched areas in lawns at spill sites.

Thatch
- Remove thatch layer if more than ½-inch thick. Thatch harbors pathogens and insect pests and prevents grass plants from properly absorbing nutrients and water.
- Prevent thatch by avoiding excess fertilizer and fungicide applications.

Water
- Water deeply (to a depth of 6 inches) when necessary.
- Water early in the day so foliage will dry quickly. Night watering (after dew appears) is not recommended during very hot, humid weather.
- If you apply too little water, wilt (blue-green color and footprints easily visible), browning, and death can occur. Some grasses (e.g., Kentucky bluegrass) will go into dormancy in drought but will green-up again when moisture returns.            
- Too much water deprives roots of oxygen, stunts growth, and promotes root and crown rots.

Light
 - Most turfgrasses will be thin and weak in shaded areas; use shade-tolerant grass seed mix.
- Selective pruning of tree branches may let in enough extra light to promote grass growth.
- Plant groundcovers in heavy shade.
                                                                                                                               
Mowing
Height
- Mow at 2½ to 3 inches, with maximum in hot, dry weather.
- Avoid 'scalping,' especially in irregular, bumpy areas.
Frequency
- Cut no more than one third of total length at any cutting so grass is not stressed.
Clippings
- Clippings can generally be left except during a disease outbreak.
Equipment
- If grass blades look brown and shredded at the tips after mowing sharpen and adjust mower blades.
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Disease

Circular patches and/or rings of dead and/or unusually green grass	- Note size and patterns. - In the morning, when grass is still dewy, look for the web-like threads of the fungus and/or mushrooms on the lawn. - Dig up a section of dying grass and examine the roots for dark color and evidence of crown and root rot.
Thin or dead grass in an irregular area	Examine individual grass blades for: (1) leaf spots (probably tan with dark borders); (2) evidence of fungus (orange, black, or white powdery spores); (3) gelatinous red threads; and (4) slimy or powdery white, orange or brown mold.

General practices that reduce disease
- Keep foliage as dry as possible.
- Mow when grass is dry.
- Landscape to allow good air circulation.
- Collect clippings when fungus is active in the lawn.
- Avoid nitrogen fertilizers early in spring, in hot weather, and just before grass becomes dormant.
- Choose disease-resistant cultivars when possible.

Insects
White Grubs: Lawn shows gradually increasing patches of thin turf; it often looks like drought stress, sometimes accompanied by skunk or raccoon damage (lawn torn out in chunks because animals are feeding on the grubs). This is usually observed from May to early June or in September and October when grubs come up to the soil surface to feed on grass roots.
Chinch Bugs: Generally, these are observed in sunny areas or on sandy soils. The problem is often confused with drought stress is usually as it is usually observed during hot periods in July and August.
Bluegrass Billbugs: This is sporadic in New England. It usually begins as yellow areas of grass along the edges of driveways and sidewalks and is usually observed in July or early August. Adults may be seen on pavement in late May or early June.
Sod Webworms: Adults are small moths that fly just above the ground at dusk. Damaged areas begin as small discrete patches that can spread into larger areas. Feeding by caterpillars occurs at night.
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Moss in Lawns
Adapted from: David P. Martin and Keith J. Karnok, Ohio State University Extension, 2001;  Dr. Sharon M. Douglas, The Connecticut Agricultural Experiment Station, 2006

The occurrence of moss in lawns is a common problem for many homeowners. Moss is usually associated with turfgrass management problems and/or soil and site characteristics. Mosses are small, leafy plants that appear to be a mass of fine stems. They vary greatly in size and do not have roots, but rather form root-like filaments that attach to soil and other substratum.

Mosses can grow and out-compete turfgrass species when one or more of the following occur: high or low soil pH (some species appear to be associated with acid and others with alkaline conditions), low soil fertility, shade, poor soil drainage, and soil compaction. Mosses are adapted to a wide range of environmental conditions – some grow well in dry areas, while others grows best in bog-like habitats. Although moss is often found in shady spots, it can also grow and thrive in sunny locations.

Cultural Control
The best way to control moss is to change the conditions that favor its growth:

1. Soil nutrition. The first step in controlling moss in a lawn is to determine the nutritional status and pH of the soil. Do a soil test and the report will make appropriate suggestions for fertilizer and lime applications to correct any deficiencies. When turfgrass species are growing under conditions of poor fertility, they are weak and are therefore unable to compete with encroaching mosses.

2. Soil drainage. Soils that are constantly wet because of poor drainage should be contoured so that water will drain away from the lawn. If moss is present in low areas of a yard or if soil drainage is a problem, it is important to determine if and how these problems can be remedied. Drainage tiles can be effective in many circumstances. However, it is important to determine the effects of the excess water on adjoining areas.
3. Shade. At least 3–4 hours of full sunlight or 6–8 hours of filtered sunlight are necessary to grow grass. If heavy shade is a problem, trees may need to be pruned and a "shade grass” seed mix used for the area. When moss is troublesome in grass under trees, there is often little that can be done. In these situations, perhaps shade-tolerant groundcovers such as pachysandra, English ivy, or myrtle should be considered.
4. Compacted soil. Heavy soils can be amended by incorporating several inches of sand, compost, or other sources of organic matter into the soil. These amendments may help to improve both soil texture and drainage. Compacted soils can also be aerated.

Chemical and Mechanical Control
Moss can be physically eradicated by mechanical removal and hand raking with a stiff-tined rake. However, control may only be temporary if the reason(s) for the infestation is not established or remedied as described above.

Moss can also be controlled through the use of chemicals. Since mosses usually grow most vigorously during the cool moist conditions in the fall and spring, these are the best times to apply chemical moss killers.
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Annual Grasses

Annual grasses are species that germinate from seed, complete their life cycle, produce seeds, and die within a year. Annual grasses are not the only undesirable grass weeds to infest lawns. There are many perennial grass species that are equally pervasive and pernicious, including quackgrass, nimblewill, brome-grass and others which are often confused with annual grass weeds. Crabgrass is the most common and troublesome weed among annual grass weeds in lawns. Others include foxtails, barnyardgrass, goosegrass, and annual bluegrass.

Cultural Control
An integrated weed management program is a combination of recommended cultural practices and the use of herbicides when necessary. Producing a dense, healthy stand of grass is the best way to control annual grass weeds and other broadleaf weeds. The proper mowing height and frequency, fertilization, and irrigation are part of any weed control program and should be practiced throughout the growing season. Learn more about Lawn Management

Chemical Control
Selective annual grass weed control can be achieved with herbicides. Preemergence herbicides provide effective control of crabgrass and other annual grass weeds for several weeks or months, depending upon dosage and products. The effectiveness of these materials is based upon their ability to provide excellent weed control with no turf injury. [NOTE: The only preemergence herbicide that will not prevent grass seed germination is Tupersan (Siduron).] Timing is important for herbicide application. It is necessary to apply preemergence herbicides before annual grass seeds germinate (which is 50 degrees F for crabgrass). The preemergence herbicides should be applied two weeks prior to the expected weed seed germination period. The best time for annual grass weed control is late April in Rhode Island. The herbicides should be watered in.
Adapted from the University of Massachusetts Extension, 1999
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Crabgrass
Adapted from the UMASS Extension, 2001 and 2006
Large crabgrass (Digitaria sanguinalis), also known as hairy crabgrass, is found in almost every crop or non-crop situation. It is a member of the grass family. Crabgrass is a rapid growing, coarse textured, yellowish-green grass that is conspicuous when found growing among fine textured, dark green, cool-season turfgrasses. The prostrate stems extend outward along the ground and are highly branched. Roots develop at nodes along the stems.

Life Cycle
Large crabgrass, a summer annual, is one of the most troublesome weeds in lawns. Crabgrass reproduces by seeds and it has a prolific tillering or branching habit. A single plant is capable of producing 150 to 700 tillers and 150,000 seeds. Crabgrass plants are very adaptive to mowing height and can produce seeds at mowing heights as low as one half inch. Crabgrass seeds are dormant for a short period of time after they shed from plants and germination is related to soil temperature: when soil temperature reaches 50 degrees F, crabgrass begins to germinate. However, soil temperature must be in this range at least for a week. Seeds germinate best from mid-spring to late summer and the plants continue to grow until midsummer when days become shorter and vegetative growth slows as plants enter their reproductive stage. Purplish seed heads form until frost kills the plants. Plants begin to die when soil temperatures fall to 50 degrees F and below.

Control Methods
The basic principles of a crabgrass control program are to prevent both seed germination and reseeding in the lawn. Crabgrass cannot be controlled in one growing season because of the great number of viable seeds that accumulate in the soil over a period of years. Therefore, satisfactory control may require several seasons of conscientious adherence to a good management program.
Cultural control
Establishing a dense and healthy stand of turfgrass is the best way to control crabgrass and other annual weeds, including grasses and broad-leaf weeds. Proper mowing height and frequency, fertilization, and irrigation are part of the weed control program and should be practiced throughout the growing season.
Seed new lawns in fall. Crabgrass and other annual grasses that germinate in late summer will be killed by low temperatures in the fall. Mow your lawn to a height of 2 to 3 inches because the taller grass shades the soil and keeps it cool, preventing crabgrass seeds from germinating. Also, avoid summer fertilization. Crabgrass benefits more from fertilizer application under high temperatures than Kentucky bluegrass and other cool season grasses.
Chemical control
Crabgrass can be selectively controlled in turfgrass by judicious use of preemergence or postemergence herbicides. Timing is important for herbicide application. The best time for application of preemergence herbicides is when forsythia blooms (i.e., late April or early May). Use caution when seeding a new lawn in the spring. Only use a crabgrass preemergence herbicide containing siduron as it will not prevent germination of desirable grass seeds whereas other crabgrass preemergent controls will.
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Insect Pests
Proper insect management on lawns is a process of detection, identification, and evaluation. It is important to remember that complete elimination of insects is impractical: try to manage the insect population at a level that does little damage to the lawn. Damage control and not insect control is the ultimate goal. Lawn damage varies with grass condition, the insect species, and its population level. Vigorous lawns can withstand greater pest numbers than severely weakened ones. Fortunately, lawn insects do not often present major problems in Rhode Island.

The mere presence of an insect may not be a problem, since not every insect is a pest. Even if the insect is a pest, its presence in small numbers may not cause a problem. It is essential to know what insect you are dealing with and what population levels cause damage; the stage or stages and time of year when it is most susceptible to control; and the best methods to regulate the populations. Insects on lawns should be controlled only when they cause damage, not simply because they exist.

Detecting the presence of an insect is the first step in good lawn insect control. Be sure to examine an area of grass that contains living as well as damaged grass plants. If the lawn looks wilted and water-starved, a root-feeding insect (white grubs or billbugs) may be involved. Some insects (chinch bugs, sod websorms) hide in the thatch and then feed on the grass blades. Damage from this type of feeding appears as brown patches when the blades are clipped off. Others live on the blades and withdraw the plant's sap.
Adapted from University of Minnesota Extension, 1997

Grubs
Many people don't make the connections between adult beetles that attack roses, grape vines, fruit trees and 150 other plants and their larvae which mature in grass. One thousand adult beetles can lay fifty thousand grubs in your lawn each year. In the summer, grubs emerge from the soil as adult beetles, completing a one year life cycle. White grubs (grubworms or simply, grubs) are the white, C-shaped larvae of a large group of beetles, several of which attack turf grasses. The most important species of beetle pests of the cool-season and transition zone turf grasses are: Japanese beetle (Popillia japonica); May or June beetles (Phyllophaga spp.); and northern masked chafer (Cyclocephala borealis).

White grubs eat organic matter, including the roots of plants. Therefore, damage first appears to be drought stress: heavily infested turf first appears gray-green and wilts rapidly in hot sun. Continued feeding by grubs will cause the turf to die in large irregular patches. Tunneling of larvae cause turf to feel spongy under foot and the turf can often be rolled back like a loose carpet. Grub populations may or may not cause observable turf injury by predatory mammals such as skunks, racoons, opossums, and moles that dig in the turf in search of a meal.

Sampling
The time to sample for grubs in Rhode Island is August 1 to September 15 – adult beetles generally lay their eggs in July and most larvae should be present by early August, although in dry years development may be slowed. Depending on soil moisture, you may need to sample more than once to make sure you "capture" the grubs developing at your site.

Furthermore, lawns differ in susceptibility to white grubs because of differences in grass species, soil health, irrigation, amount of sun or shade, traffic, etc. A dense stand of grass with a healthy root system can generally tolerate up to 10 grubs per square foot. Most white grubs seem to prefer grass in sunny areas. To determine how many grubs you have in your lawn cut back square foot samples (cutting through the turf and thatch on three sides) in several places. Peal back the turf and inspect the thatch and upper inch of soil for grubs. Populations of annual grub species that are less than six grubs per square foot are not a problem. When populations reach 10 and 15 per square foot (or more) they can cause significant turf damage.

Control Strategies
White grubs attack turf areas irregularly from year to year. The major factor influencing development of damaging numbers of grubs is soil moisture and rainfall. In general, in years with normal or above normal rainfall, grub populations increase. A well-maintained lawn next to ornamental plants that are favored by the adult beetles seems to be more commonly attacked. Also, fescues are not as severely attacked as Kentucky bluegrass and perennial ryegrass.
Water Management: Practically all white grub species require moist soil for their eggs to hatch. The young larvae are also very susceptible to desiccation. In areas where turf can stand some moisture stress, do not water in July and early August when white grub eggs and young larvae are present.
Organic Control: Milky Spore is powder that contains the bacterium Bacillus popillae which attacks grubs. Each grub that dies from Milky Spore decays and releases three billion new spores. Once all of the grubs are destroyed, the spore will remain dormant but viable in the soil until new grubs come along even years later. Three to five years are needed to provide lasting controls using Milky Spore, but it will not harm beneficial insects, animals, or humans and it is safe to use near water.
Chemical Control: There are three commonly used insecticides for grub control. These chemicals are sold under a variety of brand names.
(1) Iimidacloprid is a slow-acting, long-lasting product that prevents subsequent infestations. Apply between May 1 and June 30 in New England to maximize its effectiveness.
(2)  Trichlorfon is fast-acting and is used to spot treat.
(3) Halofenozide is an intermediate material used in late summer. It acts by interfering with a grub’s ability to molt successfully. Therefore, late summer or early fall applications will not be effective because most of the grubs have already molted. Similarly, spring applications are not effective because the grubs that are present in the spring are the same mature grubs that were present the previous fall. Therefore, appropriate timing for applications of halofenizide is late summer for Japanese beetle in New England.

Insecticide Usage
Approximately 95–99% of any pesticide used for grub control ends up in the thatch. If the thatch layer is one inch thick or more, the grubs probably will not contact effective doses of the insecticides.

Synthetic pesticides generally degrade rapidly. However, many are subject to additional degradation by bacteria and fungi and these microbes tend to build up if a pesticide is used continuously. Therefore, it is recommended to use a pesticide only once per season, when needed.

In general, irrigating after an insecticide application will improve performance for soil insect control. It is also generally recommended that grass clippings be returned to the lawn for one to two mowings after a grub insecticide application. Do not wait more than 30 days to recheck the grub infestation, especially if the original population was high. If the grub population has not been reduced below six grubs per square foot consider reapplication of another pesticide. Remember, the smaller the grubs the easier they are to kill with insecticides.
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Billbugs
The bluegrass billbug is probably the most common billbug species on lawns. As its name suggests, its primary host is Kentucky bluegrass, but it also attacks perennial ryegrass and fescues. Occurrence of the bluegrass billbug in New England is generally very sporadic, but when it does occur, it can cause severe damage.

Adult billbugs can be observed crossing paved areas on sunny days in late May or early June. In areas where bluegrass billbug larvae have been feeding actively, there will be accumulations of "frass," or insect excrement, which is white and has the texture of fine sawdust. Feeding damage usually is evident along the edges of paved areas and may resemble salt damage (except that primary billbug damage appears in late July and most of August). Eventually the damage may spread throughout the lawn.

Several cultivars of endophyte-enhanced lawn grass are resistant to bluegrass billbug feeding. Billbugs are some of the most difficult turfgrass insects to control because the adults' armor-like bodies do not readily absorb insecticides. They also do not ingest much insecticide when they penetrate a grass stem while feeding. The larvae are also difficult to control because they are boring inside grass stems for much of their lives. The most reliable timing of insecticide application for New England appears to be June, targeting some small larvae. Several insecticides have shown reasonable activity against billbugs.
Adapted from the University of Massachusetts Extension, 1999
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Chinch Bugs
There are three species of chinch bugs. They feed on the sap of grass plants and reside in thatch. The chinch bug can be a major insect pest on home lawns throughout the country. The hairy chinch bug (Blissus hirtus) is the most common species in the Northeast. It prefers bentgrasses, but will attack many other lawn grasses as well.

The chinch bug sucks out plant juices while injecting chemicals into the plant which clog the vascular system. The area around the feeding puncture usually turns yellow. Damaged areas first appear as small, irregular patches which enlarge as the insects spread. Examine grass in the marginal areas of injured patches, not in the clearly dead grass. Spread the grass gently with your fingers and look in the thatch, near the soil surface. Chinch bugs are usually very active in the summer, so you will be able to see them scurrying around, especially on warm summer days.

In many instances, chemical control of chinch bugs is not necessary. Lawns that receive adequate amounts of water throughout the summer (preferably weekly deep waterings) are able to tolerate relatively high populations of chinch bugs without sustaining damage. In addition, many lawns have natural populations of predators, such as ground beetles, which can keep chinch bug populations from getting out of hand. Insecticide applications sometimes have very adverse effects on these predators, causing the chinch bug populations to develop more rapidly in subsequent years. There is strong resistance of endophyte-enhanced grasses to the hairy chinch bug.
Adapted from the University of Massachusetts Extension, 1999
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Sod Webworm
Webworms attack grasses in New England. Characteristically, they spin threads of silk as they move, webbing leaves and soil particles together, and often form horizontal silk tubes in the thatch. Adults are small buff-colored moths that fly upward when disturbed by movement (for example, a person walking by or a mower approaching) and then dart back into the grass. However, it is the caterpillars that actually damage the grass.

Sod webworms commonly attack Kentucky bluegrass, perennial ryegrass, fine fescue, and bentgrass. Webworm damage starts as small yellow or brown patches in the leaf blades in lawn areas. As the caterpillars feed and grow, the patches gradually increase in size. Caterpillars are nocturnal, so they will not be noticed on the surface during the day. The easiest way to determine whether sod webworm caterpillars are present in a turf setting is to put one or two tablespoons of lemon-scented dish detergent in one or two gallons of water and pour the soapy solution over an area which is about two feet on each side. The caterpillars will be irritated by the solution and will wriggle out of the thatch and up to the surface, where they can be seen. Most caterpillars will respond to the soapy solution within two to five minutes.
By midsummer, large sections of the lawn may be destroyed by the caterpillars, which prefer sunny areas. Webworm damage is particularly severe in droughty conditions, in part because the turf is less able to recover from caterpillar feeding. Damage is usually most apparent in July and August, when temperatures are highest and cool season grasses are not growing vigorously. Affected areas recover slowly from webworm feeding and often are overrun by weeds.

Webworms are relatively susceptible to several insecticides. The key to successful control is to apply a control agent when most of the caterpillars are still very small. One guideline for timing of application which seems to work pretty well is to make an application two to three weeks after a peak in moth flight activity. Because webworms are nocturnal, traditional insecticide applications should be made as late in the day as possible. The material should be watered in lightlyIf possible, the area should not be mowed for two days after application.

There are also several biological control options which appear to work reasonably well for controlling sod webworms. One is a bacterium (Bacillus thuringiensis; sold commercially as B.t.). Another option is an entomopathogenic nematode.
Adapted from the University of Massachusetts Extension, 1999
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Biological Insect Control

There are ways to reduce dependence on traditional insecticides and to incorporate more "biopesticides" or other biological control options into your insect control program. "Biopesticides" are living organisms which are handled and applied in a manner similar to traditional insecticides. Examples include entomopathogenic nematodes, bacteria, and fungi.

Nematodes
Entomopathogenic nematodes are nematodes that carry bacteria inside their bodies. When the nematode penetrates an insect victim, it releases bacteria, which break down the internal tissues of the target insect, resulting in a massive infection. As the insect dies, the nematodes reproduce within the cadaver. The juvenile nematodes pick up some of the bacteria, and move on in search of new target insects.
Entomopathogenic nematodes are available commercially and appear to be effective at suppressing populations of several turf insects.

Bacteria
Some bacteria cause diseases in insects. The most common bacterium used against turf insects is Bacillus thuringiensis var. kurstaki, or "B.t.k.," for short. It is effective against several kinds of caterpillars and is much less sensitive to desiccation than the nematodes, so can be used as a foliar spray against caterpillars like the gypsy moth as well as cutworms and webworms in turf.

Another species of bacterium causes a disease in Japanese beetle grubs: Bacillus popilliae causes "milky disease" in the grubs. Infected grubs take on a very milky appearance and are very flaccid. Use of milky disease in New England is somewhat controversial, because there are no data to indicate whether the disease actually suppresses grub populations. Milky disease is available commercially.

Endophytic Fungi
Finally, there are some species of grasses which contain endophytes, which are fungi that produce substances which are toxic to certain insects. Endophytes occur in some perennial ryegrasses and fescues, and have been incorporated into some commercial cultivars. They are effective in the suppression of chinchbugs and billbug populations, and are active against cutworms and webworms as well.
Adapted from the University of Massachusetts Extension, 1999
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Fungal Diseases

Following is a brief description of the most common fungal diseases of lawns. The diseases have been categorized by symptom: patches (fungus causes dead spots or patches), rings (fungus cause rings of dead or affected grass), or leaf blight (fungus affects individual blades of grass, often over a wide area). Since most grass diseases affect leaves, patches and rings describe certain diseases in more advanced stages of development.
Adapted from Missouri Botanical Garden: Kemper Center for Home Gardening, 2001 - 2007

Symptom: Dead Spots or Patches
Brown Spot: Round patches of turf up to several feet in diameter appear watersoaked and eventually turn brown. Dark gray smoke ring is sometimes visible on lower mowed turf. Expanding patches of discolored grass up to several feet in diameter mark the presence of a severe outbreak. Where disease is severe, the affected area may look sunken. Brown patch is a disease of hot, humid weather. It is most common when night temperatures and relative humidity stay high for several days and are accompanied by rain. Disease development can be very rapid under such

There are two important cultural practices that will limit brown patch in lawns:
1. Excessive nitrogen applications cause a flush of succulent growth that is very susceptible to brown patch. Avoid nitrogen fertilizer applications just before or during hot weather. Several lighter fertilizer applications are less likely to trigger disease than one heavy application.
2. Water on grass leaf blades greatly increases infection and disease. If the lawn needs moisture, water to a depth of 6 inches early in the day, so the grass leaves will dry quickly. Do not water in the late afternoon or early evening. Avoid frequent light sprinklings. Brown patch is most severe in bentgrass, perennial ryegrass, and tall fescue lawns.

When a lawn has had previous brown patch problems, fungicides may be applied when humid weather and hot nights are predicted. Applications should continue according to the fungicide label for as long as the hot, humid weather persists. Fungicides are usually not necessary on Kentucky bluegrass/fine fescue lawns.
Adapted from the UMass Extension, 2000

Dollar Spot: Rounded, straw-colored, silver dollar-sized, slightly irregular circles 3–6 inches in diameter. Spots have a reddish margin. Cottony mycelium may be evident in the morning growing over dead tissue. Dollar spot is most common in early summer, late summer, and early fall in humid weather with warm days and cool nights. Dollar spot is less prominent in very hot weather. Turfgrasses appear to be more susceptible to infection when nitrogen deficient and when the soil is dry, probably because both factors reduce the growth of the grass plants.
Application of fertilizer will stimulate growth, so the infected leaf blades may be mowed off. Sufficient water should be applied when rainfall is sparse. Dollar spot disease responds readily to fungicides, but application of fertilizer and attention to watering practices is usually sufficient to minimize the disease. Dollar spot rarely causes sufficient injury to lawns to justify the use of fungicides.
Adapted from the UMass Cooperative Extension, 2000
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Red Thread: Red thread and pink patch are caused by two different fungi, but they often appear together and under the same environmental conditions. Lawns infected by these fungi may have a pink-to-reddish cast when viewed from a distance. If moist grass is viewed more closely, pinkish gelatinous growth of the fungi and tiny tufts of spores may be seen. In drier conditions, tiny red threads of the red thread fungus may be observed extending from the leaf tips. These diseases can be found on many turfgrass species but are seen most often on perennial ryegrasses and fine leaf fescues. The diseases are not usually very destructive. Both fungi occur mostly in the spring and fall in cool (65-70 degree F), moist weather.

Although we have no control over periods of prolonged cool, moist weather, it is possible to prevent or reduce red thread and pink patch through good lawn care practices. Soil pH should be maintained at 6.5-7.0. Watering should be infrequent and deep; avoid frequent sprinklings late in the day. Prune trees and shrubs to increase light penetration and air circulation. Soil fertility must be balanced. These diseases are most common in nitrogen-deficient turf, but be cautious about applying excess nitrogen fertilizer, especially in spring. Fungicides are not recommended for red thread or pink patch on lawns except in extreme cases.
Adapted from the UMass Cooperative Extension, 2000

Snow Mold:  Roughly circular patches (at least 3 to 12 inches) of dead and matted grass blades; damage usually becomes apparent as the snow melts and exposes the grass in late winter. Pink snow mold may initially look white and mature to a faint pink to salmon color. Gray snow mold is white to gray in color. These diseases are caused by different fungi.

It is useful to determine whether the disease is pink or gray snow mold because gray snow mold rarely damages more than the blades of the grass. Lawns with gray snow mold can be expected to recover fairly quickly even when damage appears extensive. Pink snow mold, in contrast, may invade the crowns and roots causing more serious injury. It is not unusual for both types of snow mold to be found in the same area. All common lawn grasses may be infected, but Kentucky bluegrass-fescue lawns are the least susceptible to severe damage. Fungicide applications for snow mold are not recommended for home lawns except in extreme circumstances.

The most important means of preventing or reducing snow mold problems in lawns is the care of the grass at the end of the summer season. As long as the grass continues to grow, it should be mowed. Fall fertility programs should be timed so that they do not influence the ability of the grass to become dormant for the winter season. Fall fertilizers should be applied more than six weeks before dormancy, or they should be applied after leaf blade growth has stopped but while the grass is still green. Addition of nitrogen fertilizer just before the grass becomes dormant will stimulate a late burst of succulent green growth, making the grass prone to winter injury caused by frost, ice, or exposure and also providing the snow mold fungi with vulnerable host plants.

Because snow mold activity is greatest beneath covers that maintain moist conditions, all leaves or other materials should be removed from the lawn. In addition, it is best to avoid piling snow deeply along sidewalks and driveways where it will form a long-lasting snow bank. In large lawn areas, the strategic placement of snow fences and landscape plants may prevent deep drifting of snow. In the spring, rake away dead and matted foliage from damaged areas to allow the new growth to begin.
Adapted from the UMass Extension, 2000
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Pythium Blight: Rounded sunken patches up to 1 foot in diameter. This disease begins in mature lawns as small slimy or greasy looking spots. The spots may assume a reddish color if weather conditions become cooler and drier. When the turfgrass is wet or where air circulation is poor, the cottony, white, weblike mycelium of the fungus maybe observed. This disease can develop rapidly and extensively in poorly drained areas. It occurs most commonly in perennial ryegrass lawns. Pythium blight is not a common lawn disease in New England.

In established lawns, water to a depth of 6 inches when necessary. Water early in the day; avoid watering in the late afternoon and early evening. Prune landscape plants to encourage air circulation. Avoid excessive nitrogen fertilizer, especially when hot, humid weather is expected. Mow lawn when dry to avoid spreading the fungus. Mow low or poorly drained areas last. When necessary, several effective fungicides specific for Pythium diseases are available.
Adapted from the UMass Cooperative Extension, 2000

Symptom: Rings
Necrotic Ring Spot: Despite the different names, necrotic ring spot and summer patch have essentially identical symptoms which include rings and circular patches of dead or dying grass. Sometimes there is a center of relatively healthy grass in the "doughnut" or "frog-eye" patch. Both diseases are most severe on Kentucky bluegrass lawns that were seeded or sodded two to four years previously. Fine-leaf fescues are also susceptible. Severe damage is most common on sodded Kentucky bluegrass lawns that have been planted on poorly prepared sites with poor drainage and compacted soil.

Symptoms often become obvious in warm to hot, dry weather when the lawn becomes stressed. Areas along driveways, walls, sidewalks and other places that are heat- and water-stressed will often show symptoms first. Necrotic ring spot infects lawn grass in spring and fall in wet weather, but symptoms become severe when environmental stress conditions impact the diseased plants from early summer on. The fungus that causes summer patch is more active in hotter weather, so summer patch symptoms are most severe in mid-summer, especially following a heavy rainfall. The times of occurrence of these diseases overlap, so it is not always possible to separate the diseases strictly by season or symptoms.

Penetrant, systemic fungicides can help prevent these diseases but are not generally cost-effective. Because of the expense and difficulty in fungicide applications to turfgrass roots, the cultural controls described above are strongly recommended for lawns.
Adapted from the UMass Extension, 2000
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Summer Patch see Necrotic Ring Spot

Symptom: No Pattern
Powdery Mildew:  Powdery mildew may appear quite suddenly, usually in shaded areas, and most commonly on Kentucky bluegrass. The grass blades look as if they were dusted with flour or lime. Later, the leaf may turn yellowish and begin to dry up and die. Powdery mildew is most common on grass from July to September, and occasionally in the spring. It is most common during overcast periods of cool, moist weather.

Powdery mildew is usually a disease of shaded grasses. Prune shrubs and tree branches to reduce shade and increase air circulation. If grass is thin or weakened in shady areas, re-seed with shade-tolerant grass species and select cultivars resistant to powdery mildew. In moist, shaded areas of lawns, powdery mildew may be prevented or reduced by careful lawn care. Avoid excess nitrogen fertilizer, raise the mowing height, and water deeply but infrequently. Avoid frequent, light sprinkling. Fungicides are not recommended for powdery mildew control on lawns.
Adapted from the UMass Cooperative Extension, 2000

Leaf Spots: Leaf spots on grass leaf blades begin as small red to purplish ovals that later develop tan centers of dead tissue with darker borders ("eye spots.") When turfgrass is succulent from recent nitrogen fertilization and there is abundant moisture on the leaf blades, numerous leaf spot infections per blade can occur. The leaf spots may then coalesce and cause extensive blighting. The fungus may even invade the crowns and roots, leaving the plants weakened and rotted. This severe stage is called "melting-out." Large areas of dead or badly weakened grass may result.

Keep in mind that mowing increases infection by leaf spot fungi in the following ways:  wounds are made that allow easy penetration by the fungi; new spores are produced in abundance clippings; mowers and feet spread spores. If only scattered leaf spots are observed, no significant harm should come to the lawn. Severe damage is the result of repeated infection of stressed plants. These practices should limit disease to an acceptable level: Avoid excessive early spring nitrogen applications with water soluble fertilizers.  Water infrequently and deeply. Never water in the late afternoon or early evening. Prune landscape plants to allow good air circulation. Avoid frequent light sprinklings. Mow high to avoid plant stress and mow frequently. Collect clippings when numerous leaf spots are observed to reduce spore production. Do not mow when grass is wet.
Fungicides should not be applied routinely for leaf spot fungi. If cultural management has not prevented severe infection or if prolonged wet weather occurs, several contact fungicides are available.
Adapted from the UMass Extension, 2000

Rust: The disease appears as small, reddish spots on the leaves. The grass may not look particularly diseased until after the infection is well developed. In fact, because spore production does not occur until one to two weeks after infection, rust-infected grass leaf blades are usually mowed away before rust spores can be produced. In rare severe infections, the lawn may look thin and be weakened and more susceptible to other stresses such as drought or winterkill. Rust is most common on Kentucky bluegrass and perennial ryegrass and it occurs mostly in late summer and early fall.

The most important way to avoid rust infection on lawns is to keep the grass growing vigorously so that it will be mowed before spores can be produced. Balanced fertility,   aeration, thatch removal, and adequate water supply are among the important factors that will optimize grass growth. Watering practices that keep foliage dry as much as possible will also help reduce infections. Fungicides are not recommended for rust diseases on lawns except in extreme cases.
Adapted from the UMass Cooperative Extension, 2000
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Usefull Websites

The Home Lawn: Controlling Insects (University of Minnesota Extension)             
Lawn Diseases (North Dakota State University Agriculture and University Extension)              
Lawn Diseases (University of New Hampshire Cooperative Extension)               
Managing Home Lawn Diseases (University of Illinois Extension)
Preventing Lawn Disease: General Recommendations (University of New Hampshire Cooperative Extension)