Turf Disease Watch – Turfgrass Science at Purdue University

Turf Disease Watch

The near term forecast indicates an early arrival of summer, when temperature and moisture conditions favor diseases that can cause serious damage to turf on golf courses, athletic fields and residential landscapes.  Two of the more important diseases are discussed below.

Brown Patch 
Brown patch is a foliar disease that does not damage crowns or roots. Moderate to severe outbreaks on high-maintenance creeping bentgrass and annual bluegrass can result in thin, poor quality turf that may be predisposed to algae and moss infestation.  Brief episodes of brown patch activity can temporarily spoil the appearance of putting greens, tees and fairways. Taller mown turfgrasses for athletic fields and professional landscapes, especially tall fescue and perennial ryegrass, also may sustain damage from brown patch infection.
On creeping bentgrass and annual bluegrass putting greens and tees, brown patch development results in well defined circular patches, ranging from 4 to 12 inches in diameter. Leaf blades within the patches turn brown after infection, while a gray-white band may evident at the perimeter of active patches.  Images of brown patch field patterns and symptoms are described in my Turf Disease Profile on brown patch (BP 106-W) available at the following link:http://www.ag.purdue.edu/btny/Extension/Pages/TurfPathology.aspx

Numerous effective fungicides are registered for brown patch control.  In many parts of the United States brown patch occurs sporadically.  Therefore, other more chronic turf disease threats should be considered when selecting fungicides for brown patch control.  For example, flutolanil and the QoI fungicides provide excellent brown patch control, but they are not effective against dollar spot. If they are applied without an appropriate tank mix partner during a period of dollar spot activity, the dollar spot problem could become overwhelming and very costly to control. 

Pythium Blight
Pythium blight outbreaks are especially damaging to perennial ryegrass, rough bluegrass, creeping bentgrass, and annual bluegrass. Kentucky bluegrass and tall fescue can be infected, but disease development is limited and turf is rarely damaged. Among turfgrass diseases, Pythium blight receives considerable attention because it spreads very quickly, affects leaves and crowns, and kills plants, resulting in extensive loss of the turf stand. The Pythium pathogen is classified as an oomycete and is closely related to fungal pathogens.
Pythium blight occurs during the most uncomfortable days of summer, when dew periods are long (greater than 14 hours) and evening temperatures average 68°F or higher. Outbreaks often are first observed in low areas or swales, where more soil moisture is maintained and dew begins to form early in the evening and remains through the morning. Late afternoon rain during these hot, humid periods further favor disease development and may be responsible for rapid spread of the pathogen. Turf with lush growth and excessive nitrogen fertility is especially vulnerable to infection.

The hot, humid weather should signal an alert for Pythium blight outbreaks. Initial symptoms include small, circular patches of collapsed, water-soaked leaves and stems on close-mown turf.  If observed early in the morning, infected plants may have cottony white mycelium. Infected turf dies and becomes matted. Images of Pythium blight field patterns and symptoms are described in my Turf Disease Profile on Pythium blight (BP 109-W) available at the following link:http://www.ag.purdue.edu/btny/Extension/Pages/TurfPathology.aspx

Because of the pathogen’s survival and spread characteristics, Pythium outbreaks normally occur in the same “problem” areas each year when extreme weather conditions prevail. In high–risk areas or on greens where mycelium is evident, morning mowing should be delayed until surfaces are dry. Precautionary spot treatment with fungicides on problem putting greens and tee boxes is advisable.
Fungicides with very good efficacy against Pythium blight (if applied preventatively) include mefenoxam (Subdue Maxx) and propamocarb (Banol), Newer fungicides targeting Pythium include fluopicolide (Stellar) and cyazofamid (Segway).  All four of these fungicides products are expensive and only control Pythium blight, so be sure that you have an accurate diagnosis before selecting a product to resolve the problem.

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