David Robson: Too much rain can lead to a sickly lawn

Rain is wonderful unless you have too much or not enough, or the side effects of too much.

Too much rain often brings lawn diseases.

Few ornamental trees, shrubs and flowers have suffered from this year’s excess moisture, but lawns have taken a beating.

Most lawn diseases are caused by a fungus (bacterial and viral diseases are practically unheard of), or the weather.

Most turf grasses, especially cool-season bluegrass, fescues and ryegrass, love moisture but are rather poor at seeking it out. They prefer having water right at their roots.

When it rained seemingly every other day this spring, grass roots thought they had it made. They grew thick, sending out more shoots. Of course, we had to mow more, but lawns looked green.

However, like Aesop’s grasshopper, which didn’t stock up for the winter, the grass roots also got caught when hot, dry conditions rolled around. All of a sudden, the soil where the roots were starting drying out. Then shoots started turning brown right and left.

Spring-seeded lawns were particularly susceptible. Conditions were a little too ideal for plants to germinate and grow. The roots didn’t need to grow deep looking for cooler conditions and moisture.

Some seeded lawns have massive dieback, and there isn’t anything to do except wait until fall and seed again. Fall traditionally provides a better lawn — temperatures start to cool, and roots aren’t stressed as much by heat.

Watering may help, but it should be a deep, thorough soaking, wetting the ground at least 8 inches deep. Once the top part of the soil starts drying, roots will sense the moisture deeper and hopefully start growing toward it. Unfortunately, they don’t grow fast.

Far worse is the damage being done by various lawn diseases.

Turf diseases come and go, often occurring after wet springs followed by dry summers.

The past two years, while soggy, haven’t yielded as many diseases due to cooler temperatures and the consistency of the rain week after week. The last month has been drier and hotter, though — exactly what fungal spores need to infect turf.

Most turf grass diseases start out as a general yellowing of the grass. Most of us fail to see it. It happens slowly, and we tell ourselves it’s just the way the light is hitting the grass.

Then, faster than you can sneeze, patches of grass up and die.

If you look at dead turf, you usually don’t see anything except dead grass. For signs of disease, look at the transition area between what’s dead and what’s living. That means getting down on your hands and knees.

Usually, the grass blades surrounding dead spots will have some purplish-brown discoloration on the leaves, possibly as banding, hourglass-shaped lesions, or just plain spots.

Some diseases are easy to describe. The Dollar Spot starts out as 2-3 inch-diameter dead patches that eventually grow together to form irregularly shaped areas. Helminthosporium starts out as larger irregularly shaped areas that grow into even larger misshapen dead patches. Rhizoctonia brown patch does something similar.

Then there is Necrotic Ring Spot and Summer Patch, which used to be called Fusarium Blight, but really is two different disease organisms that always seem to be together. The results are the same: smaller dead areas that eventually merge into larger ones.

It’s next to impossible to prevent the diseases, except with good lawn practices and disease-resistant grass cultivars.

Most diseases are caused by cultural practices coupled with weather conditions. Change some of your practices, including aerating, dethatching, watering deeply and fertilizing in the fall more than spring, and you will reduce the chances of diseases.

The vast majority of fungicides on the market are preventative, not curative. If you sense you have a problem, change how you manage the lawn instead of spraying something that may or may not work.

The other alternative is to make sure the lawn is constantly in a young stage by introducing new disease-resistant cultivars every three to five years when you overseed. Many newer types have resistance built in, and when combined create a more resilient lawn.

In the meantime, if you have dead patches, all you can do is rake out the dead, water the remaining lawn deeply and infrequently, and wait until the first of September to reseed.

David Robson is a horticulture educator for the University of Illinois Extension. For more gardening information or for your local extension unit office, go to www.extension.uiuc.edu/mg.