Pythium Induced Root Dysfunction
Pythium induced root dysfunction (PRD) unlike other Pythium diseases, occurs during warm, dry weather, in drought prone areas, and in high sand content root zones with good drainage. Primarily a disease of creeping bentgrass, this disease is most commonly found where 1) native soil established greens are overlaid with several inches of sand and 2) on newly established, sand-based creeping bentgrass greens. PRD is caused by Pythium volutum, P. aristosporum, and other newly described species of Pythium. Root infection occurs at soil temperatures between 54-70 ºF; symptom expression is delayed until the turf experiences heat/drought stress. As long as growing conditions remain optimal for turf, the pathogen and plant coexist without evidence of disease.
Turf foliage appears yellow to brown and plants are prone to wilting before plant death. A generalized thinning and decline of turfgrass stands develops. Symptoms first appear in drought prone areas and root systems of affected turf are shallow and lack root hairs. Infected roots die back more rapidly than uninfected roots subject to heat stress. Death of the plant often results from the mechanical injury resulting from mowing stressed plants with a dysfunctional root system. Cultural methods for managing PRD include those practices which stimulate root growth.
- Improve drainage and aerify as needed. Excessive organic matter accumulation in the root zone of a sand-based green can hold excess moisture.
- Raise mowing height above 0.125 inches and reduce mowing frequency, rolling greens daily to maintain green speed and quality. Maintain increased height until turf recovers.
- Irrigate carefully based on turf needs rather than a schedule, hand water severely affected areas, or add a wetting agent to improve water penetration into the root zone.
- When PRD is active, avoid mowing when the turf is wet to prevent mechanical damage to weakened turf.
- Pay attention to nitrogen fertility as this syndrome is most prevalent in areas of low N fertility. High N encourages Pythium, while low N can hinder recovery.
- Consider using a walk behind mower. Relieve soil compaction if present.
- Overseed as soon as possible after an outbreak.
Management with Fungicides
Preventive chemicals are recommended in areas of past Pythium problems as fungicides are more effective when applied preventively. In areas of past PRD infection, start fungicide applications when soil temperatures reach 50-75 ºF. Repeat applications in the fall when soil temperatures again fall to 50-75 ºF. Fungicide applications should be applied in 4-6 gallons of water/1000 sq ft or watered in with at least 0.125 in of irrigation.
For a listing of fungicides currently labeled to manage this disease, refer to the Disease Management chapter of UMass Extension's Professional Guide for IPM in Turf for Massachusetts.
Written by: M. Bess Dicklow