Lawn Disease Control

Lawn Diseases & Disorders

Brown Patch (rhizoctonia blight)
Brown patch is the most common disease of tall fescue in the southeast, but most other cool- season grasses are also susceptible – a soil-borne fungal disease caused by different strains of the Rhizoctonia blight fungus, and is unlimited to the different turf grass it can affect. Thankfully, Brown Patch is an ascetic-only disease and will not kill the turf. But how does the fungus infect the lawn? For most fungal diseases, the answer is a combination of human error and favorable growing conditions. The pathogen lives dormant in the soil and survives the winter underneath thick thatches until the weather becomes warmer and wet. Even though the peak growth activity occurs at temperatures of 70°–85°F with high humidity levels, the disease will start to show growth once the night air temperature reaches between 40° – 70°F when the humidity levels begin to rise and the presence of a nearby susceptible host. The optimum conditions trigger the fungus to advance to the next stage in its life cycle – spore development and infection. The pathogen infects leaf tissues nearest the soil. Conditions that weaken the turf such as mowing with dull blades, mowing below the recommended height and improper watering practices. Just like us, diseases jump at the opportunity of a free meal.
SIGNS & SYMPTOMS As the name implies, Brown Patch appears in irregular circular areas of brown and diseased turf often surrounded by a narrow, dark brown or gray ring called a “smoke ring” which is evidence of active fungal growth. The interior may display a healthier green color. Patch size can range from a few inches to several feet in diameter. As a self-diagnosis, pulling blades of grass at the edge of the infected area. If the leaf blades can be extracted easily from the stems and appear brown and rotted at the base of the blades, it’s an indication that you have Brown Patch and should be treated quickly to stop the disease from spreading.

Gray Leaf Spot (Pyricularia grisea fungus)
Gray Leaf Spot is a fungal lawn disease and is very common in St. Augustine grass and may cause problems in ryegrass and tall fescue. The disease occur in very hot, humid weather and is more severe in newly established turf areas in shade location and area with poor air movement. It can produce large amounts of infectious spores in a very short period of time causing an evident decline in symptomatic tissue. Germination occurs within a few hours after contact with a susceptible host with symptoms appearing within hours of infection. Mowed leaf tips provide the best invasion to the leaf tissue, keep blades sharp and avoid high nitrogen fertilizers which promote succulent leaf tissue for this disease pathogen! The pathogen kills the plant from severe leaf blight and symptoms develop rapidly with warm temperatures above 80°F, high and again humidity, and prolonged moisture.
SIGNS & SYMPTOMS May rapidly change, first exhibiting tiny lesions, which often go unnoticed, before enlarging to round, brown to tan colored spots measuring 2-5 cm boarding and band surrounding the infected tissue. Thinning of grass blades may occur and lesions may become so numerous on leaves they consume them altogether. In later stage development, the discoloration may turn purple to brown with a more oval-shape spot. Severe outbreaks of the disease may cause the turf grass to appear burned or scorched.

Large Patch (rhizoctonia solani)
Large patch is a common issue in warm-season turf which is very common in the southern turf like Zoysia grass and is referred to by some cases as Zoysia patch. Other warm-seasons grasses which are most susceptible to this pathogen are centipedegrass and St. Augustinegrass. Bermuda grass has occasionally affected but recovers from the damage so quickly that there is little cause for concern. The large patch developed in the fall and spring when temperature is cool and when the warm season grows the slowest. The symptoms usually start to appear in the spring as the grass starts to green up from winter dormancy, although they can be seen in the early fall and early winter in Zoysia grass since it is the slowest to go fully dormant. Large patch is encouraged by wet weather, excessive nitrogen in the fall and spring, poor soil drainage, over-irrigation and low mowing heights.
SIGNS & SYMPTOMS Irregular brown, yellow to orange patches of thin turf 1 to 2 feet in diameter, but can expand to yards. Multiple patches can merge together to form huge areas systematic turf. Reddish-brown lesion form on the leaf sheath but not on the leaves themselves. As the disease progresses, the leaf sheath and crown of the infected plant become rotten and greasy looking.

Dollar Spot (Sclerotinia homoeocarpa)
Dollar spot is caused by the fungal pathogen Sclerotinia homoeocarpa. The pathogen blights leaf tissues does not affect turf grassroots or crowns, but it can be a persistent disease in several turf grasses. Susceptible in cool season are bent grass, Fescue, bluegrass, and ryegrass. Susceptible species in warm season are Bermuda grass, Zoysia grass, and occasionally centipede and St. Augustine grass. Disease symptoms commonly result in poor turf quality and appearance. The disease occurs from early spring through late autumn, but is most active under conditions of high humidity and warm daytime temperatures and cool nights. The disease infects by producing mycelia, which can be spread to plant parts, mechanically or foot traffic from one area to another. Dollar spot is favorable in warm humid weather conditions and is more severe on nitrogen-deficient turf. Dollar spot worse in humid conditions on soil that is typically dry. Cycles of warm day and cool nights encourage dollar spot because of heavy dew formations on the grass. Excessive thatch and low mowing heights also encourage its development.
SIGNS & SYMPTOMS On closely mowed turf, small bleached white spots from 1 to 2 inches diameter develop and can look similar to chemical or pet urine burns. This disease symptom is also easily confused with the early stages of Pythium blight. On higher mowed turf the spot may expand into patches exceeding 5 inches in diameter. Early in the morning or when conditions favor prolonged high relative humidity, the white cottony of the fungus mycelia of the fungus can be seen in the infected turf patches.

Pythium Blight (pythium aphanidermaturm)
Pythium Blight is also known as cottony blight, spot blight or grease spot, and is a destructive turfgrass disease. Pythium blight affects grass in the summer when the temperature and humidity are considerably high. Grasses infected with Pythium Blight often go undetected by lawn owners because, in the early morning, turf infected with Pythium Blight appears to look wet with dew and darkly colored green. The effect of Pythium Blight also results in infested grasses looking greasy or oily. When the weather becomes hotter, this infected grass begins to wilt at an alarming rate, turn brown and then dries and dies out. In other cases, a sign of the disease is white, cob webbish, mold-like growths of the fungus appearing on the leaves and blades of grass. At worst case, the solution to fighting the disease is changing your grass entirely and starting from scratch which may not be ideal with how time-consuming and expensive that would be. Common names associated with Pythium Blight include cottony blight and grease spot.
SIGNS & SYMPTOMS If humidity levels stay high, especially at night going into early morning, a white fluffy mass of mycelia may appear. Sometimes this is called the “cottony blight” phase. If conditions remain favorable, the spots may grow bigger in a short amount on time. In the early morning, a light gray ring may or may not be present along the outer edge of the spot. The spots are typically round irregular 1 inches in diameter on closely mowed turf can be up to several inches in diameter. On higher mowed turfgrass appear more suddenly. The leaves in infected spots are water-soaked, slimy to the touch and copper-colored, dark brown, or black when the disease is active. Spot can appear straw-colored or tan lesions with no distinct border between disease and green and tissue. In general the leaves in the center of the disease patches are completely blighted and appear dead.

Fairy Ring (Mycelia Fungi)
Fairy Rings which are caused by fungi start to show signs of activity during the end of spring or early summer and produces toxic substances that accumulate in the soil and kill the turf. Fairy rings are easily recognizable with distinct dark green rings and/or fruiting bodies including mushrooms, toadstools and puffballs. The rings can be full or part circle. Although there are thousands of types of fungi that cause these rings, there are in fact only 3 types of Fairy Ring, each having different characteristics. Fairy Rings start from a central point and gradually increase in size, with the rings getting larger as time passes. In most cases they increase about 80mm – 150mm in size each year. Fairy Rings degrade the organic matter in the lawn, it is then broken down bymicroorganism and released as nitrogen. The nitrogen is then made available for plant uptake, giving the lawn its distinct dark green ring. They can be found in all types of lawns and turf, including luxury lawns, golf greens, sports fields and neglected turf.
SIGNS & SYMPTOMS Fairy ring appears as arcs of green stimulated turf that range from a few feet to many in diameter. These rings are stimulated turf and may not be accompanied by an adjacent areas of dead or declining grass. when the turf becomes stressed, the rings may become brown. During a period of heavy rainfall, mushroom or puffball fungi may appear adjacent to the ring and persist for a few days. Fairy ring is very difficult to control or eliminate altogether. Old wood, stumps and other woody organic debris are left in the turf root zone below the surface. Some cheap topsoil, many in bulk from landscape supply centers have large portions of ground stumps and tree debris that can lead to a smaller outbreak of this disease. It is also best to avoid the manmade topsoil with high large amounts of mulch mixed in them and not use them as a base or even mix with existing soil for new turf installations which can carry the pathogen spores from old ground stumps and roots of tree s which can lead to this disease in smaller but yet noticeable volumes.

Other Common Disease Problem in Southern Lawns

Helminthosporium Disease

Spring Dead Spot

Microdocchium Patch (Pink Snow Mold)

Good Common Sense Practices to Combat Common Lawn Disease Problems

• Proper mowing etiquette
  Keeping the turf height at the recommended level and sharp mower blades are the first line of defense. Do not mow wet grass. Not only will it create ruts in the ground, stain clothing, and clog mowers, both man and machine will become disease carriers.
• Pruning
  Pruning of surrounding trees and shrubs in the infected areas will help to dry excess moisture caused by excessive shading.
• Improve turf grass root system
  Good soil drainage and core aeration reduce soil compaction and thatch accumulation to increase soil porosity.
• Avoid spreading the disease
  Do not walk through infected areas when it is wet, nor allow pets to roam through the wet grass. And again, do not mow wet grass.
• Avoid over-watering
  Remember this hint? Fungus thrives in excess moisture. Eliminate or limit watering in the evening. Morning watering is always the best time.
• Encourage healthy root system
  Low areas that hold water are more susceptible to disease due to all the excess moisture. Good soil drainage and core aeration reduce soil compaction and thatch accumulation to increase soil porosity.