Q: We are renovating high-traffic areas this summer while the school fields are closed. What should we do about diseases like Pythium?
A: 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 and humid weather. Warm nights over 70 degrees F with hot days over 85 degrees 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, 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. Check the NTEP website (NTEP.org) to see which cultivars show more resistance, and work with your seed rep to choose cultivars with optimum germination and establishment conditions for that turf species.
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). The seed coating 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. There are both liquid and granular formations available. 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.
Damping off caused by pathogens such as pythium can be devastating turf diseases that can lead to areas needing to be re-planted. The best strategy for avoiding damping off disease on new turf is to use sound management practices, be vigilant during optimal environmental conditions, and have a preventative plan in place.
Pamela Sherratt is a sports turf extension specialist at 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
