Chapter 6 Flashcards
Diseases of Turfgrass
Many diseases occur on turfgrasses in Tennessee; most are cause by ______ and _________. Environmental or management factors such as wilt, cold damage or soil compaction may result in problems resembling diseases. Susceptible plants, a favorable environment and a pathogen are required for a disease to develop. For best control, chemcials can be used preventatively; however knowledge of the pathogen’s life cycle is critical. Usually chemicals are applied in a curative program after a disease is present. This requires rapid identification and proper chemical selection and application.
fungi and nematodes
______ ______ up to 3 feet in diameter develop in hot, wet weather on cool season grasses. Tall fescue is most affected. “smoke rings” composed of grayish fungal mycelium (vegetative bodies of fungi that appear as branching, threadlike filaments) and dying grass often develop at the margin of patches of closely mowed grass when the disease is growing rapidly. Patches up to 20 feet in diameter can develop on hybrid bermudagrass during cool, wet weather in the spring. Good soil drainage, proper irrigation amounts, proper soil ph and low levels of nitrogen fertization help reduce severity. Fungicides should be applied when symptoms first appear. Hosts: bentgrass, ryegrasses, tall fescue, hybrid bermudagrass
Brown Patch
This disease is characterized by small, straw colored patches, 1 to 3 inches in diameter, which are easily visible aftger mowing. Many patches may come together to form larger, dead areas. Lesions are formed on the edges of leaves. Leaves are girlded and the upper leaf dies. It is most prominent in the spring and fall during warm, moist weather, but continues to develop during humid weather in the summer. Adequate nitrogen fertilization and soil moisture levels will help prevent development of this disease. Hosts: bentgrass, ryegrasses, bluegrass, zoysiagrass, and bermudagrass
Dollar Spot
______ ______ appear as small to large rings of very green grass. Grass inside the ring may be in decline. Mushrooms or puffballs may appear on the edge of the ring during warm, moist weather. The soil within the ring may become very dry and difficult to water. Rings often continue to enlarge for many years and ring diameter can range from 1 to more than 100 ft. Removing thatch and maintaining proper soil moisture may prevent fairy ring development. Aeration and extra watering may help grass outgrow damage. Some fungicide drenches may provide control. Hosts: all turfgrasses
Fairy Rings
Circular patches develop in cold, wet weather. Patches are rarely larger than 6 inches in diameter without snow cover and up to 2 feet with snow. Affected grass appears gray or light brown and becomes pink after exposure to light. _____________ often develops under tree leaves left on turf for long periods, but is most severe under snow. Avoid heavy fertilizer application before cold, wet weather or prolonged snow cover. Remove fallen tree leaves. Apply fungicides before snow or when the disease is first observed. Hosts: bentgrass, bluegrass, fescue, ryegrass
Fusarium patch
Several fungi cause these leaf, crown and root diseases. Leaf spots appear as small, purple-to reddish brown, circular lesions that may enlarge and girdle the leaf, causing light brown turf. Thinning out and fading-out symptoms may occur during stress when roots and crowns are affected. Infection occurs in spring and fall, but the worst damage occurs during summer droughts. Avoid overfertilizing and overwatering and use resistant cultivars. Apply fungicides during early stages of disease development. Host: Nearly all turfgrasses
Helminthosporium-type Diseases
A white-to-gray, powdery growth of mycelium develops on infected leaves, which turn yellow and die slowly during heavy infestations. Weakened plants may be killed under stress. Feritilize, mow and irrigate properly and reduce shade. Select shade tolerant cultivars. Several fungicides will provide control. Host: bluegrass
Powdery Mildew
The blight first appears as small spots 1 to 12 inches in diameter. Diseased leaves are at first water soaked, soft and slimy. In very humid weather, cottony mycelium may appear. The disease spreads rapidly during hot weather in damp areas or following rain or irrigation. The shape of the diseased are may follow drainage patterns. Root rot type symptoms develop in hot or cold, wet weather and cause thinning of the turf. Good soil drainage and air circulation and low levels of nitrogen fertilization reduce severity. Some fungicides will not control _________. Preventative applications work best. Host: bentgrass, ryegrasses
Pythium or Cottony Blight
Circular or irregular shaped patches of grass die rapidly during cool, moist weather in spring and early summer. Large areas are affected when many patches join together. This disease develops from the tip of the leaf downward. Leavs may be covered with red mycelium and ____ ______ may develop from cut ends of leaves. Fertilize and irrigate adequately. Avoid long periods of excess water on leaves. Remove infected clippings. Some fungicides will provide control. Hosts: bentgrass, bluegrass, fescues, ryegrasses
Red Thread
____ _____ begins as small, yellow flakes on leaves and stems that enlarge, on leaves, to yellow spots with raised centers or pustules. The pustules may rupture to release yellow, orange, red, or dark brown spores. Turf may become spore colored in severe infections. Infected plans turn yellow and weaken and may die under stress. It is most frequently found during cool, wet weather in the fall. Fertilize and irrigate properly to reduce damage. Keep leaves free of excess water by watering in the morning, improving air circulation and reducing shade. Resistant cultivars are available. Several fungicides provide control. Hosts: bluegrass, ryegrass, tall fescue, zoysiagrass
Leaf Rust
Fungal fruiting bodies of various colors may suddenly appear on leaves in small patches. Usually they appear during or after extended periods of warm, wet weather. Although unsightly and the cause of yellowing of affected leaves, slime molds are not true pathogens of turfgrasss and are not harmful. Remove by brushing, mowing or washing. Fungicides are not necessary, but some can be used for control. Hosts: nearly all turfgrasses
Slime Molds
______ _____ ______ - first appear in 3- 5- year old bermudagrass in the spring. The spots appear in the same place and expand for three or four years. After two to three years it appears as rings of dead grass and then disappears after three to four years. Bermudagrass usually grows over the spots during the summer, but infectedareas remain lower than surrounding grass and are frequently invaded by weeds. Reducing nitrogen levels and thatch may reduce severity. Impove cold hardiness by applying potassium in late summer and increasing mowing height. Fungicides can be used. Host: Bermudagrass
Spring Dead Spot
Infection is most noticeable in the spring and fall when plants appear slightly yellow or brown. They become stunted, root growth is reduced and leaves become stiff and erect. Leaves turn gray, then black and split lengthwise to reveal black spore masses. Plants often die under drought stress. The smut fungus grows rapidly in cool, moist weather but high temperatures hasten death. Drought stress kills infected plants. Proper fertilization and infrequent, deep watering helps infected plants. Resistant Kentucky bluegrass cultivars are available. Several fungicides provide control. Host: bluegrass, tall fescue
Stripe Smut
This disease appears as distincly ____ _______, 1 to 2 feet in diameter; small, white mushrooms develop on leaf blades. Blades die first at the tips and later down the leaf to the sheath. Surviving plants usually fill in thinned areas. Hot, humid weather favors white patch. It usually occurs in newly established lawns less than 2 years old. Proper management practices and soil ph helop to overcome this disease. Host: Tall fescue
White Patch
________ Kill or stunt roots, resulting in slow growth, thinned turf, poor response to fertilization and irrigation, rapid wilting during drought and increased weed invasion. They are most damaging in light soils. Only a ________ assay of soil samples can determine if ______ are a problem. Fall is the best time to assay. Select ______ resistant species and fertilize and irrigate properly. Nematicides are usually needed for the sting ____ on high maintenance turf. Host: all turfgrasses
Nematodes
