Rhizoctonia large patch of zoysiagrass is active in the fall. The pathogen, Rhizoctonia spp., can infect the leaves and sheaths of zoysiagrass until the turf goes dormant. Patches appear initially small (a few inches in diameter) that can rapidly increase in size. The outer edges of the patches often appear to have a tinge of orange. Although the zoysiagrass often recovers from this disease, bermudagrass often invades these weakened areas. Fungicides are available for the control of this disease.
Iron chlorosis was appearing in many trees in late August 2000. The yellowish leaves are quite apparent in trees like the pin oak.
Gray leaf spot was reported in areas of Kentucky, southern Indiana and Illinois in mid-August 2000. Although this disease is primarily associated with perennial ryegrass on golf courses and athletic fields, it is quite devastating on high cut ryegrass that can be found in lawns. The symptoms of this disease are often confused with drought symptoms.
Physiological leaf scorch develops on trees in areas where hot dry weather is occurring. As these plants begin to transpire, water loss is greater than water being absorbed by the root system. The leaves begin to scorch or brown.
Brown patch (pathogen: Rhizoctonia solani) was causing damage on tall fescue lawns throughout the transition zone during late June 2000. The hot humid weather present in the transition zone had brought this disease on. Nitrogen applications during conditions favorable for brown patch should be avoided or minimized. In some cases fungicides may be necessary.
Rough bluegrass (Poa trivialis) samples were beginning to show up in plant disease clinics across the U.S. in late June 2000 This light green colored "bluegrass" is susceptible to heat and drought stress. There is no current control for this grass.
Slime molds may be present on home lawn turfs in areas that have received considerable rain. Slime molds appear rather suddenly as white, purple, or orange patches. The colorful patches are the result of the fruiting structures produced on the leaves. The fungi use the grass blades to support their reproductive structures. Slime molds are not pathogenic. Thus, control of this lawn problem is not necessary. However, if the turf becomes unsightly the spores can be removed by washing them off with water from a hose, raking the turf, or frequent mowing.
Powdery mildew is a disease that attacks a number of ornamental plants. Conditions favorable for powdery mildew include warm humid overcast days with cool nights. Given these conditions powdery mildew is most common during late spring and early fall but can occur anytime during the growing season. This disease is common on plantings that are crowded, damp and shaded. Powdery mildew initially appears as a white to grayish-white coating on leaves, shoots or buds. As the season progresses, the powdery mildew coating is dotted with small dark brown specks (fruiting bodies).
Red thread continues to be a problem on Kentucky bluegrass and perennial ryegrass turf throughout the northern U.S. as of May 2000. Although this disease is easily controlled with fungicides, increasing the fertility of these lawns should effectively decrease the severity of this disease.
Red thread is a serious problem in many Kentucky bluegrass and perennial ryegrass turfs. Generally, these turfs are somewhat deficient in nitrogen. Increase nitrogen to decrease the severity of the disease. If the disease persists, a fungicide application may be recommended.
Perennial ryegrass is especially susceptible to red thread. Circular bleached out areas often form in lawns. The diagnostic key to this disease is the presence of red threads (stroma) protruding from the leaf blade.
Red thread (causal agent: Laetisaria fuciformis) is a serious spring disease of Kentucky bluegrass, fine fescue and perennial ryegrass during periods of heavy dews, fog, and light rains. Circular to irregular shaped patches form that are straw to pinkish in color. A diagnostic key for this disease is the presence of red threads (stroma) coming out of the leaf blade. In addition, pink cottony balls (small in diameter) may be present (especially on perennial ryegrass). Sometimes this heavy reddish mass of mycelium causes confusion with pink snow mold. Red thread is especially severe on slow growing, nitrogen deficient turf. Nitrogen applications can help reduce the severity of the disease but avoid excessive nitrogen rates.
Dollar spot (pathogen: Sclerotinia homoeocarpa) was beginning to appear on Kentucky bluegrass and perennial ryegrass turfs in the northern U.S. in late June 2000. The patches often appear as circular straw patches measuring a few inches to several inches in diameter. The lesions have a bleached out center with brown borders which often have an hourglass shape appearance. In some instances symptoms may be confused with bluegrass billbug symptoms.
Dollar spot (pathogen: Sclerotinia homoeocarpa) will begin to appear on some Kentucky bluegrass lawns in early spring. This disease is generally a sporadic and minor problem. However, in some cases it can be severe. The symptoms appear as bleached out or straw colored patches. These patches may be a couple to several inches in diameter. The leaf lesion has a bleached out center with a brown border. The lesion is also shaped like an “hour glass.”
Melting out (pathogen: Drechslera poae) on common Kentucky bluegrass is especially severe this year in areas where cool wet conditions have prevailed. The disease is often most noticeable after mowing. This disease is most severe on older leaves, which are located closest to the soil surface. After mowing, these older leaves are more exposed. Preventative measures include using resistant Kentucky bluegrass cultivars. Fungicides can also be used if the disease is severe.
Cedar apple rust is apparent in early spring on junipers. The fungus produces colored galls or "spore horns" that are bright orange.
Melting-out of Kentucky bluegrass becomes more apparent in areas that have been wet and cool. This fungus causes a general thinning of the turf. Leaf lesions appear as a circular bleached out center with a purple border.
Melting-out (causal agent: Drechslera poae) is a serious disease of Kentucky bluegrass during cool wet weather periods of spring. The lesion appears purplish black, often with a yellow ring around the lesion. The overall turf symptoms can appear as circular to nondescript thinning of the turf. Culturally it is best to apply nitrogen fertilizers at rates that encourage moderate spring growth. Excessive growth due to fertilization should be avoided. In the long term reduce thatch since excessive thatch enhances the disease severity.
Apple scab has been reported in many regions of the temperate U.S. throughout spring 2000. Apple scab symptoms on leaves appear as olive colored spots with fuzzy borders. Severely infected leaves may drop prematurely. Apple scab is most severe on apple and crabapple but can also occur on mountain ash, hawthorn, cotoneaster, and pyracantha.
The apple scab fungus (Venturia inaequalis) initiates infection at time of bud break. Cool and rainy conditions favor the initial infection by this fungus. The ascospores overwinter in fruiting structures called perithecia present on leaves and old fruits. With the coming of early spring rains, these spores are splashed up on newly emerging tissue, causing infection. The ascospores will continue to infect until petal fall. Lesions appear brown to olive green with feathery margins. If infection is severe, leaves will curl and become distorted.
Melting-out is a serious disease of Kentucky bluegrass lawns in the spring. It can also cause damage on tall fescue and perennial ryegrass. The disease is caused by the pathogen Drechslera poae. The leaf lesions appear as reddish to purplish spots on the leaf. These lesions are sometimes surrounded by a yellowish or chlorotic ring. Cool, humid weather is ideal for this pathogen to infect turf.
Typhula blight is a common snow mold of the northern U.S. and is first apparent at snow melt. Symptoms appear as circular areas ranging from 6 inches to 3 feet, of light yellow, straw or grayish turf. All turfgrasses are susceptible to this disease. Cultural control measures include avoiding heavy nitrogen applications in the autumn that promotes succulent growth. Excessive thatch and compacted soils seem to enhance the severity of this disease. In the spring, light applications of nitrogen can be made to the infected area. Raking the infected area may also stimulate recovery. If the turf does not respond, you may need to reseed those areas.
Microdochium patch or pink snow mold often occurs in conjunction with Typhula blight. This disease, however, does not require a snow cover like Typhula blight. Microdochium patch appears as circular patches that appear initially as an orangish-brown color. The control measures for this disease are similar to those for Typhula blight.
Anthracnose was prevalent in spring of 2000 on many shade trees including ash, maple, oak, sycamore and walnut. Diseased leaves appear "scorched" along the leaf margins and veins. This disease is most severe when leaves are moist. Leaves infected with anthracnose will often drop. Twigs and branches may die back if the tree is in poor health and the infection is severe. Generally, anthracnose does not cause serious damage to healthy trees.
Anthracnose, a common disease of ash, oak and maple was not much of a problem in drought areas during 1999. However, leaf scorch can be mistaken in these areas for anthracnose.
Dogwood anthracnose can be a problem in the southeastern United States. Generally this disease is more severe in woodland sites than in more open landscape sites.
Dogwood powdery mildew is common in autumn and is present through most of the southeastern United States. This disease can cause leaves to turn a reddish color. Eventually, some leaf deformation will occur with the diagnostic whitish cast to the leaf occurring due to the fungus. This disease appears to get worse with each passing year (We don't know why.).
Pink snow mold and Microdochium patch are names given to the disease caused by Microdochium nivale. This disease can begin to occur in areas of the country where temperatures are between 32 and 46 F and cloudy, rainy conditions exist. This disease does not require snow mold. Heavy thatched lawns and lawns receiving excessive nitrogen fertilization are at risk.
Rust was appearing on Kentucky bluegrass and perennial ryegrass turf in early July, 2000. This disease is usually indicative of turfgrass that is not growing. Factors of slow growth include moisture and heat stress and low fertility.
Rust caused by the pathogen Puccinia graminis is present on turfgrasses that have slowed growth. Rust can be especially severe on perennial ryegrass, tall fescue and Kentucky bluegrass. Symptoms appear as yellow-orange postules on the leaf blade. If the infection is severe enough, walking through the turf will result in one's shoes turning an orange color. The best control for rust is to keep the turfgrass growing. A fertilizer application is a cultural practice that will reduce the severity of the disease. If necessary, fungicides are available to control the disease.
Summer patch and necrotic ring spot, caused by the pathogens Magnaporthe poae and Leptosphaeria korrae, respectively, are two major diseases of cool season turfgrasses during the summer. Kentucky bluegrass is especially susceptible to these diseases, and oftentimes symptoms are expressed during summer stress times. Symptoms can vary but are usually circular patches of straw colored turf that develop with a circular green patch in the middle (frog eye pattern). Weeds like crabgrass and yellow nutsedge will often invade the blighted turf areas. Curative control with fungicides is difficult and results are often mixed. Practices that promote recovery, like nitrogen fertilization and frequent irrigation, should be practiced. Overseeding the diseased areas with perennial ryegrass is also practiced in the northern U.S.