The Ohio State University

Home SportsNotes Summer patch symptoms on Kentucky bluegrass have appeared in the last few weeks mainly in southern Ohio. Summer patch caused by the pathogen Magnaporthe poae colonizes Kentucky bluegrass roots during spring and early summer, but symptoms do not show until later in the summer.

Upon arrival of hot dry weather of summer the root systems dieback and become dysfunctional.(photo courtesy of Dr. Richard Smiley, M. poae infected root system on the right)

Symptoms appear as irregular shaped patches, rings or crescents when temperatures rise (85-95 F). Summer patch symptoms are consistent globally as this picture taken in Dalian, China, shows.

The patches often are described as "frog-eye". Symptom expression is most severe when wet conditions are followed by dry or droughty conditions. Disease symptoms are chronic appearing in the same locations year after year.

A disease sign is the presence of weeds growing in the center of the patches. The weed types include dandelion, crabgrass, and plantain - to name a few.

Cultural Practices

Cultural management practices that help reduce the severity of summer patch include relieving soil compaction, providing adequate fertility, and planting where applicable resistant Kentucky bluegrass cultivars.

- Some cultivars of Kentucky bluegrass have shown some tolerance to summer patch, as shown in this photograph from a Kentucky bluegrass cultivar trial. A susceptible cultivar is on the left. For more information on cultivar susceptibility or tolerance consult NTEP Trials. In some instances, overseeding infected areas with perennial ryegrass is an effective method. Perennial ryegrass is more tolerant of summer patch than Kentucky bluegrass.

- Promoting good drainage and reducing soil compaction are practices that can reduce the severity of summer patch but are best accomplished in the autumn. The photograph to the left was taken from one of our core cultivation studies several years ago. The turf was Kentucky bluegrass. The column on the left received no coring treatments (notice the severity of summer patch), the middle column received 3 corings, and the column on the right 6 corings.

- From a growth perspective, a healthy vigorous (not over stimulated) growing turf is more likely to recover. Nitrogen applications during the summer should be moderate and if possible apply a slow release fertilizer instead of a quick release.

- Drought stress increases the severity of the patch diseases, thus proper watering is important. Minimize drought or wilt injury through frequent (syringing) applications of water. The lack of a functional root system limits the amount of water taken up by the root system.

Chemical Control

Fungicide applications reduce the severity of summer patch but do not eradicate the problem. Timing is critical in fungicide applications. The best program is to treat preventatively with an application made in spring when soil temperatures reach and remain above 65 F at the 2 to 3 inch level. A second application is made one month following the initial recommendation. Given the pathogen attacks the roots the fungicide should be applied in 4 to 5 gallons of water per 1000 square feet and watered in following application. Fungicides should always be used according to labeled instructions. Fungicides labeled for use on summer patch include azoxystrobin, fenarimol, myclobutanil, propiconizole, thiophanate-methyl, traidimefon, and trifloxystrobin.

Posted by Karl Danneberger & Pamela Sherratt