What's up with the wheel tracks and how do I prevent it from happening again?

Unwanted mowing pattern

We get a lot of nice comments on our mowing pattern but this happened to us last week when it was really hot. What’s up with the wheel tracks and how do I prevent it from happening again?

Iowa City

The problem is Ascochyta Leaf Blight that is almost always triggered by high temperature and rapid drying conditions. The most difficult part of this disease is pronouncing the name Ascochyta when you are trying to talk about it to your boss, so it goes like this: “ass-co-kite-a.” Just Google “ascochyta turfgrass” and you will get lots of good general information that I will pick apart for you in this column.

The fungal spores called conidia grow and are splashed around during periods of frequent rain or irrigation. The organism may be present from late spring through the summer, but it usually begins the leaf blight phase only after a period of suddenly hot weather. Predicting an Ascochyta outbreak is difficult because the exact conditions for blighting are not clearly understood and the disease symptoms appear haphazardly throughout the summer.

When the conditions are right the bleached and blighted leaves will suddenly appear. One day the grass looks fine and then suddenly you have lots of tan grass and clearly defined mowing streaks in just a day or two. The mowing streaks probably abrade the grass allowing easy entry of the infectious spores into the plant.

Look for bleached leaf tips that are collapsed. It looks devastating because the top part of the plant is severely damaged but the crowns and lower stems are seldom killed. The good news is that you can anticipate 80-100% recovery within 3 weeks, but in severe cases some turf loss may require reseeding.

Taller and less frequent mowing is recommended but most of you are locked into mowing schedules based on field use and performance. It is interesting to note that Ascochyta blight in home lawns will only occur in full sun areas and it stops where the shaded lawn has less heat stress.

In my 40 years of messing with grass I have never seen it as bad as it has been in the past 2 years in Iowa. Normally we don’t recommend a preventative fungicide because it occurs to haphazardly and a curative fungicide doesn’t help after the leaf tissue is blighted. However, after 2 years of seeing this occur in late June and early July on the same fields I will be applying a preventative fungicide trial next year in mid-June to see if controlling the fungus will reduce the wheel tracking injury.

I have mowed plenty of grass that is wilted during hot conditions without seeing any wheel tracking so I guess it is the combination of fungal presence, hot weather following frequent rain or irrigation, and mowing at the wrong time that all lines up to give a mowing pattern that you really don’t like to see. Even if you don’t have a nice striping mower try to mow nice straight lines… at least you can brag on your mowing talent if Ascochyta comes to town.