ISU Extension News

Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915

6/23/03

Contacts:
Barbara Ambruzs, Plant Pathology, (515) 294-1741, ambruzsb@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu

Yard and Garden Column for the Week Beginning June 27, 2003

Frog Eyes in Your Lawn? Maybe it's Summer Patch.

By Barbara Ambruzs
Extension Plant Pathology
Iowa State University

As land is developed for homes and businesses, landscape plants are often added to help beautify the terrain. Trees and shrubs are planted and, of course, lawns are laid down.

Sodded lawns may develop problems if good cultural practices for planting and establishment aren't followed. One of the common maladies associated with sodded lawns, primarily Kentucky Bluegrass, is summer patch. This isn't to say that this disease occurs exclusively on sodded Kentucky Bluegrass lawns. It can also be found in other situations, such as lawns with high nitrogen fertility, heavy traffic, moisture extremes, and thatch problems.

As the name suggests, this fungal disease becomes apparent during the summer. Summer patch is sneaky because infection takes place in roots early in the spring, long before above ground symptoms appear. Magnaporthe poae, the soil dwelling fungus that causes summer patch, is an ectotrophic root-infecting fungus. This just means that it lives outside plant roots. Dark mycelium (fungal threads) grows on the roots. For the fungus to feed and infection to occur sections of the mycelium swell and form a little cushion. A sticky substance holds the cushion to the root while another part of the fungus pushes its way into a root cell. In this way the fungus sets up a feeding relationship with the plant.

When infected plants become water stressed later in the season, damaged roots aren't able to provide sufficient water to the grass. By the time the 6 to 10 inches in diameter circular patches appear, roots are significantly damaged. Often, the patches will have green centers, which may either be a weedy species or the recovering grass species. This type of patch or ring is called a frogeye. Several frogeye patches are usually found in diseased areas. However, frogeyes don't always develop. Instead, the patch may be a solid straw-colored dead area.

Preparing the site before laying sod is key in summer patch prevention. First of all, make sure that construction debris, such as chunks of concrete and asphalt are removed. If the area is compacted, till the area. If topsoil is added it should be incorporated with the soil. A fertilizer can be added to promote the growth of healthy roots and the soil can be lightly moistened before putting down the sod.

Be careful not to let unlaid rolls of sod dry out. If necessary, sprinkle water on them to maintain moisture. Water the sodded area immediately after installing. The newly sodded area should be protected from foot traffic or other disturbing events until it's established.

Once the sod is down, water it daily for the first two weeks. If the weather is particularly dry and warm, additional water may be needed mid-day. You'll know if the sod is establishing or knitting into the soil layer when it becomes difficult to separate it from the ground. At this time daily watering isn't usually necessary. In general, established lawns should be watered deeply and infrequently during dry weather.

The mowing height should be 2.5 to 3 inches. The general rule is never to take off more than one third of the leaf area. Leaves are necessary for grass plants to collect energy from the sun. When grass is actively growing, frequent mowing may be necessary.

Any practice that promotes healthy root development is great for managing summer patch. Improving poor site conditions, such as soil compaction, thick thatch (a layer of dead and living plant parts that accumulate just above the soil surface), and poor drainage by core aerating in the spring or fall can provide significant benefits.

Fungicides are labeled for summer patch, but are ineffective if they aren't used along with good cultural practices. Once symptoms appear, it is generally too late to effectively chemically treat for the disease that season. The first application should be made in the spring when the soil temperature reaches 65 degrees F during the hottest part of the day.

Using blends or mixtures of turfgrass species and/or varieties can help reduce the chance for severe root disease problems in the lawn. This is a good way to avoid serious leaf disease problems, as well.

The ISU Extension publications listed below are great resources for creating and maintaining a healthy lawn. A healthy lawn with a healthy root system will be less prone to summer patch.

Sodding a new lawn, PM 491
Maintenance fertilization of turfgrass, PM 1057
Turfgrass management calendar: Kentucky bluegrass lawns, PM 1063
Mowing your lawn, PM 1213
Thatch control in the home lawn, PM 1756
Establishing a lawn from seed, PM 1072

These publications can be ordered through any ISU Extension county office or by calling the Extension Distribution Center at (515) 294-5247.

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Editors: A color photo, suitable for publication, is available at right. Click on the thumbnail photo to go to the fullsized photo. The fullsize photo is 196K.

Caption: Summer Patch


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