Tech Notes Issue 2
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Photograph: Rapid bllight
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Rapid Blight Can Hit Bentgrass Under Salt Stress
Rapid blight (pathogen: Labyrinthula terrestris) can occur on winter grass or creeping bentgrass greens. Symptoms appear as irregularly shaped patches of yellow or brown turf ranging from 5 cm to 2 meters in diameter. Rapid blight outbreaks are associated with dry periods associated with high salt content in the soil or through irrigation water. Creeping bentgrass or winter grass growing on soils with salt readings above 2.7 dS m-1(Saturated Paste Extraction Method 1:1) are predisposed to this disease. If this disease is a concern, frequent leaching needs to be done to reduce salt levels.
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A Sign of Summer Stress is the Presence of Anthracnose
Anthracnose is a destructive disease of wintergrass (Poa annua L.) and to a lesser extent creeping bentgrass greens. The pathogen, Colletotrichum cereale (formerly C. graminicola) spends most of its life cycle as a saprophyte, primarily in the thatch. However, with the arrival of high temperatures and humidity, this fungus becomes pathogenic infecting leaf, stem or root tissue. The disease is most prevalent on
shortly mowed greens but can occur at higher heights of cut found on fairways.
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Anthracnose initially appears as small patches of yellow to reddish-brown turf 2 to 5 cm in diameter. These patches can progress into relatively large irregularly shaped areas. Plants weakened by environmental or mechanical stress, are predisposed to attack by the pathogen at the stem and basal region of the plant. If the infection is severe enough the plants are easily pulled from the turf. As the infection progresses, the pathogen will produce small black protrusions immediately below the leaf epidermis. These smooth protrusions represent the early stage of the reproductive structure called the acervuli. As the acervuli matures spines (called setae) are produced.
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Photograph: Acervuli with setea
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Cultural practices to reduce the severity of anthracnose include reducing shade affects to the turf, fertilize or more specifically spoon feed through the summer to preventnutrient deficiency, and watch carefully watering practices. Too much or too little water can increase anthracnose severity. Anthracnose is a difficult disease to control curatively. Fungicide control is most effective as preventative applications. To increase the effectiveness of curative fungicide treatments, try to reduce the severity of management practices. Examples of reducing management practices might include changing from double cutting to single cutting, using a walk behind mover versus a triplex, switching to solid rollers, and reducing the number of rollings and verticutting
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