Dr. Grow: Brown patches in yard might be fungus problem

Grass can succumb to lawn disease such as brown patch.

The last few days have been very hot and extremely humid due to all of the rain. I've heard comments like "I feel like I'm going to melt." "The humidity is so thick that I can cut it with a knife."

What I find interesting is that different people have different responses to weather conditions depending upon their own personal experiences. The comments above suggest to me that the speakers are not used to humidity because they spend most of their time inside in air conditioning.

My response when I hit the door early in the morning is totally different. My background in the lawn-care business gives me a mental image of dead areas in lawns due to fungi growing rapidly because of the weather conditions. I'm sure every golf course superintendent is thinking the same thing. They are wondering if the greens they maintain are going to be green or are they going to have brown dead areas.

Within the last week I've had several calls from concerned lawn owners who have seen brown patches in their lawns get larger and larger. They want to know what is going on and what they can do about it. Because of the concern, I thought you also might be interested.

Fungi that cause lawn diseases are found in most soils all of the time. If you look closely at a stand of grass, some diseased plants can almost always be found. Although the disease is present, it is not widespread and growing aggressively.

During this time of year, we experience high humidity conditions and warm temperatures. These conditions result in a lot of moisture in the form of dew on grass blades at night. When all of these conditions are just right, lawn disease causing fungi grow rapidly and a lawn disease outbreak occurs.

There is more than one disease that causes problems in the Heartland. Brown patch, dollar spot, leaf spot and melting out are the ones typically found here.

The presence of disease can be related to the types of grass grown. Some species and varieties of grass are more susceptible to disease than to others. For example, brown patch and dollar spot are frequently found in tall fescue. Leaf spot and melting are often found in bluegrasses.

I want to caution you on one thing. All brown spots in lawns are not the result of disease. Some insects can cause brown spots, as can doggie urine. Make sure you identify your problem before you take action to treat it.

To positively identify each disease, the causal organism should be cultured in a laboratory. In the field you can be fairly certain of identification if you look at both the gross configuration of the brown areas in your lawn and at the affected leaf blades.

Brown patch, the most common disease in tall fescue, exhibits large irregular light brown patches. The leaves show brown areas in the middle of a leaf blade that are surrounded by a brown to red margin. The brown area looks like a target that is larger in diameter than the width of the fescue blade.

Dollar spot starts out as small brown spots that are the size of a silver dollar. As the disease progresses, these small spots coalesce and become larger irregular brown areas. If you look at the brown areas early in the morning, you will find what appears to be cobwebs at or near the soil surface. These "cobwebs" are really the fungus body or mycelium. When the grass dries off later in the day, these mycelium shrivel up and are no longer visible.

Dollar spot shows up on individual leaves as brown areas that have an hourglass design. The brown area in the middle of the leaf is surrounded by a brown to red brown margin.

Helminthsporium leafspot is a disease usually found in bluegrass and also in fescues early in the growing season. The stand of grass looks like it is slightly off color. Blades of grass have brown spots on them, which are surrounded by a reddish-brown margin.

As the season progresses, the Helminthsporium leafspot fungus progresses down into the crown and slowly kills affected grass plants. The resulting melting out stage appears as if the turf is slowly dying or melting out.

There are some cultural practices that will help slow down the disease. First make sure that if you water, you water early enough in the day so the grass blades are dry before the onset of darkness. Free water on grass increases relative humidity in the turf and is a requirement for the disease-causing fungi to grow on the grass blades.

Make sure you do not over fertilize in the spring. If your turf is too succulent from too much nitrogen, it becomes more susceptible to disease infection. On the other hand, light applications are needed to keep the turf growing if infection does occur.

Do not plant hedges or install fences that reduce air movement. Air movement inhibits dew formation and therefore reduces the rapid growth of the disease-causing fungi.

Mow your lawn frequently. By lowering the height of the turf, more light and air penetrate to the soil surface, thus reducing humidity in the turf. Lower humidity results in a slower growth rate of diseased-causing fungi.

Aerate your lawn on a routine basis. This increases the ability of the soil under your turfgrass to dry out sooner, thereby decreasing the relative humidity in the turf.

Because we live in the "fungus capital of the world" when it comes to plant diseases, the cultural practices suggested above may still not be enough to eliminate the disease problems in your lawn. You may have to resort to the use of fungicides.

The use of daconil on your lawn at 21-day intervals will help eliminate all of the diseases listed above. Use the curative rate if the disease is present in your lawn. If you can still find some benomyl at your local garden center, it will also do a good job on control.

If you find your lawn is consistently attacked by diseases, then consider making preventative applications of fungicides prior to the onset of the disease. When making fungicide applications before the disease is present, the preventative rate can be used. This rate is usually a lot less than the suggested curative rate. Remember, always follow label directions when applying fungicides.

If you live in the Heartland and want to maintain a nice lawn, it will have some disease problems. You can reduce the disease potential by proper cultural practices. Unfortunately, because of our climate, disease can still become a problem. Fungicide applications may still be needed.

If all else fails, there are two final solutions to the lawn disease problem. Wait for the weather to change, or plant your entire lawn in flowers.