Craig Longnecker, Perficut Lawn & Landscape
Summer wheeling tracking by mowers has once again been sighted in Iowa. The picture sent to me by Kreg Longnecker from Perficut on 25 May shows wheel track injury to an irrigated lawn in Des Moines. A week of extremely dry and windy conditions caused some pockets of turf wilting to occur and preceded the turf injury symptoms. There is no way of predicting the type of year we will have but late May through June is the time we usually see this disorder. The wheel tracking associated with Ascochyta or drought/heat stress is unrelated to product application by lawn care companies. Follow the links at the end of this article for previous updates and pictures related to this problem in both 2010 and 2011. We have been able to isolate the fungus Ascochyta from lawns showing symptoms of tan/bleached leaves in both wheel tracked areas and injured lawns without wheel tracks. This is important information but we are still not sure how the fungus, dry stress conditions, and tire tracking all fits together in terms of making recommendations to reduce turf injury.
What we know
- The symptoms have been reported late May through June in 2010, 2011, and 2012.
- Depending on the severity of injury and post injury growing conditions, damaged areas will take from 2 to 4 weeks to recover. Recovered lawns can be reinjured throughout the summer if conditions favorable for injury reoccur.
- Symptoms can occur without prior wilt but usually moderate wilt precedes injury, especially wheel tracking symptoms.
- Symptoms are bleached tan to white upper leaves with some leaf tips collapsed (see links below for several descriptive pictures of the problem).
- The problem is more frequently observed in newer subdivisions where lawns are less than 10 years old. Lawns in older mature landscapes, especially with large shade trees, seldom show this problem.
- The problem seems to be more problematic on Kentucky bluegrass, moderate on perennial ryegrass, and seldom occurs on tall fescue.
- The symptoms of wheel tire streaking associated with Ascochyta or drought/heat stress should not be confused with fertilizer burn or pesticide phytotoxicity.
What we don’t know
- There is a lot we don’t know about this disorder. Here are some of my observations and internal questions that I still struggle with. You can help me by sending pictures, information and opinions describing this problem. My phone and email contact is at the end of the article.
- In most cases the best looking lawns in the neighborhood seem to express the most severe injury. Lawns with automatic irrigation and higher fertility may express more injury.
- Iowa sod produces produce excellent quality sod, however many lawns in new subdivisions have been sodded on very poor quality subsoil using newer varieties of Kentucky bluegrass. Your comments related to the role that sod, age of lawn, soil quality, and grass variety play is needed.
- While we have isolated Ascochyta from injured plants we are still trying to determine if the problem is more related to the fungus or more associated to a direct injury caused by wheel stress on wilted turf. You can help by sending samples to the ISU Plant and Insect Diagnostic Clinic to confirm presence or absence of Ascochyta when these symptoms are observed. The cost for disease identification is $20.
Plant and Insect Diagnostic Clinic
327 Bessey Hall
Iowa State University
Ames, IA 50011-3140 USA
Recommendations at this time
- The recommendations are a work in progress since research information is lacking on Ascochyta and wheel tracking.
- Mow taller to reduce wilt stress and less frequent to reduce the number of events when injury could occur.
- Fungicides are not recommended at this time because of the uncertain role that Ascochyta plays in the disorder and the unpredictability of disease occurrence. We are however making preventative fungicide applications from late May through June 2012 in areas where the problem repeatedly occurs to help us determine the role that Ascochyta plays in wheel tracking.
David D. Minner, Professor
Extension Turfgrass Specialist
Ames, IA 50011