We are renovating high-traffic areas this summer while the school fields are closed . What should we do about diseases like Pythium ?

Q & A WITH PAMELA SHERRATT

The vast majority of turfgrass diseases are caused by fungi , and most soils contain fungi that can cause seedling diseases . Pythium , Rhizoctonia and Fusarium are the main culprits . Pythium damping off is a concern if seeding and overseeding with susceptible turfgrasses such as perennial ryegrass . Pythium has a short incubation period , which means the time period between infection and visible symptoms is very short . Because of this , by the time a turf manager knows that Pythium is there , it may be too late for the turf , and it will rarely recover , meaning that re-seeding is needed .

Damping off disease occurs in hot , humid weather . Warm nights over 70 ° F with hot days over 85 ° F , with humidity over 90 % and wet weather is the optimum environment for this disease . Diagnosing Pythium is best done in the early morning when leaf tissue is dew-laden or wet . Signs of the disease itself may include tufts of fungal mycelium . Upon closer inspection of the turf , symptoms show tissue that is blighted , collapsed or dead . Affected plants often appear brown / black , water soaked and slimy . The leaf tissue is tan colored and shriveled when dry . Localized spots quickly grow to several inches wide . Take pictures and measure the infected areas , to monitor infection and recovery rates . To reduce the spread of damping off , avoid mowing wet turf in hot , humid conditions — especially if there are signs or symptoms of the disease .

The condition that affects Pythium the most is moisture . Over-applying water creates wet leaf tissue that encourages the disease . It is critical for the seedbed to have good drainage and for water to be applied during the day rather than overnight . Irrigating early in the morning will help to wash dew off foliage , which will also reduce the incidence of seedling diseases . Without regular water , newly seeded areas will not germinate and establish . In essence , it is a balancing act between applying enough water for seedling establishment , but not so much water that the leaf tissue is constantly wet . The disease favors turf that has more than 10 hours of leaf wetness per day for several consecutive

days . Excessive nitrogen also compounds the problem . An application of starter fertilizer with a slow-release source of N is a standard practice for successful seed establishment . Don ’ t apply more until the turf has matured . Additionally , it is important to seed turfgrasses at the right rate . Applying too much seed can result in overcrowded growing conditions that hold moisture and prevent each seedling from maturing . This results in a weak stand of turf that is more prone to disease .

There are turfgrass cultivars that show more resistance to diseases such as damping off ( NTEP . org ), but no cultivar is immune , and seedling turf is more susceptible than mature turf . Once seedlings reach a certain level of maturity , they are more likely to outgrow damping off , so the initial couple of weeks of a seedling ’ s life are the most critical .

Due to its quick incubation period , it ’ s best to have a plan to prevent damping off rather than control it . One option is to buy seed that has been coated with a fungicide ( often referred to as “ Apron-treated ” seed ), which provides control of seedling diseases for the first few days of seedling life . A study I conducted at Ohio State suggested that around 10 days of protection can be obtained by using this type of seed coat . A more cost-effective and popular option is to apply a preventative fungicide like Subdue ( mefenoxam ) during the establishment period — particularly if environmental conditions for the disease are favorable . If you aren ’ t sure if it ’ s Pythium or Rhizoctonia causing the disease ( it ’ s very hard to tell the difference ), it may be more effective to use a strobilurin fungicide . Seedlings that are treated in time may only be thinned by the disease . If applied at the time of seeding — either to the seed or foliage of the new seedling — fungicide can provide control . SFM

Pamela Sherratt Sports turf extension specialist The Ohio State University

Questions ? Send them to Pamela Sherratt at 202D Kottman Hall , 2001 Coffey Road , Columbus , OH 43210 or sherratt . 1 @ osu . edu

Or send your question to Dr . Grady Miller , North Carolina State University , Box 7620 , Raleigh , NC 27695-7620 , or grady _ miller @ ncsu . edu

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