Lawn fungus - Knowledgebase Question

Aurora, Il
Question by mooremx
April 9, 2008
For the last 2 years I have had very bad summer-patch and dollar spot. The 1st year this happened (summer-patch only) I treated the lawn with Spectracide Immunox and got great results. The 2nd year I failed to pretreat the lawn with a fungus treatment and got it worse and the dollar spot. I will be pretreating this year. What do you recommend I do to get rid of any chance of this fungus coming back? I am not over watering, watering at night, under watering, or over fertilizing. Thanks.


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Answer from NGA
April 9, 2008

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You're dealing with two different pathogens here so you may have to apply fungicides at specific times rather than make a single application. Here are the basics:

Dollar spot is common on all cool season turfgrasses. It is caused by a fungal pathogen that survives in local soils and infected turf residue. Dollar spot is generally considered a disease of late spring and early fall, when night time ambient temperatures range between 50? and 60? F and long dew periods prevail. However, symptoms may be apparent throughout the summer, if environmental conditions remain favorable. Outbreaks of dollar spot are more likely to occur in turf that is growing slowly due to environmental stress and nitrogen deficiency. New dollar spot patches arise with the transport of infected grass clippings. Individual spots enlarge as the pathogen grows outward from an infection center.

The disease is called dollar spot because the spots produced on short mown golf course turf are approximately the size of a silver dollar. It reveals how long this disease has been studied, because silver dollars have been scarce for the past 40 years or more. The spots are much larger on turf that is maintained at heights of 2" or greater. On warm, humid mornings, the pathogen produces patches of cottony growth that may resemble signs of Pythium infection. Symptoms on individual leaves are characterized by bleached white lesions with distinct brown margins. These lesions often have an hourglass shape and extend across the width of the leaf blade.

The strategy for preventing intolerable dollar spot outbreaks is based on maintaining vigorous turf with adequate nitrogen fertility during the latter weeks of spring and early fall. Timing irrigation to avoid prolonged dew periods is another factor contributing to disease control. Deep, infrequent irrigation can be helpful in minimizing dollar spot outbreaks. Cultivars of various turf species with slight resistance are available. Dollar spot is readily controlled with a few timely applications of protectant and systemic fungicides if conditions warrant chemical application.

Summer patch and necrotic ring spot are root diseases that primarily attack Kentucky bluegrass, although other species including annual blue grass and tall fescue may be affected. They are caused by different pathogens, but because they are indistinguishable from based on visual symptoms, summer patch and necrotic ring spot are referred to as 'patch disease' out of convenience. Patch disease often occurs in mature stands of turf that are three or more years old, but occasionally affect younger stands. When ample moisture is present, infection can occur over a broad range of temperatures. Summer patch is favored by warm wet conditions; necrotic ring spot is favored by cool wet conditions. Symptom expression of summer patch is associated with heat and drought stress. Symptoms of necrotic ring spot may occur throughout the growing season.

The pathogens survive in the soil and in infested plant tissues. The most significant mechanism for their spread is movement of infested root, crown, or stem tissues during turf maintenance practices.
Summer patch and necrotic ring spot are root diseases that primarily attack Kentucky bluegrass, although other species including annual blue grass and tall fescue may be affected. They are caused by different pathogens, but because they are indistinguishable from based on visual symptoms, summer patch and necrotic ring spot are referred to as 'patch disease' out of convenience. Patch disease often occurs in mature stands of turf that are three or more years old, but occasionally affect younger stands. When ample moisture is present, infection can occur over a broad range of temperatures. Summer patch is favored by warm wet conditions; necrotic ring spot is favored by cool wet conditions. Symptom expression of summer patch is associated with heat and drought stress. Symptoms of necrotic ring spot may occur throughout the growing season.

The pathogens survive in the soil and in infested plant tissues. The most significant mechanism for their spread is movement of infested root, crown, or stem tissues during turf maintenance practices.

I'd use Immunox Lawn Disease Control and apply every 14-28 days as long as symptoms are present.

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