Now that the snow has melted in most of New England and turfgrass has begun to green-up, it is time to start thinking of some of the typical springtime turfgrass diseases that occur. Over the next week or so we will be posting management updates for turfgrass diseases that make yearly appearances in the spring or should be preventatively treated for if there is a past history of disease occurrence.
Today's disease is yellow patch (or cool season brown patch) caused by Rhizoctonia cerealis. Yellow patch commonly occurs on Agrostis and Poa turfgrass species. Symptoms typically appear as yellow or brownish rings or arcs on golf course putting greens (symptoms may appear more diffused on taller cuts of turf) (Fig. A). Patches range from 6 inches to 3 feet in diameter and may appear irregularly shaped if multiple patches or rings coalesce. Annual bluegrass seems to be the most susceptible. Creeping bentgrass appears to be more susceptible to the disease than velvet bentgrass (Fig. B). Temperatures between 50-65 °F during cloudy or wet periods are most conducive to disease development. However, temperatures below 45 °F or dry, sunny conditions with temperatures above 75°F will interrupt disease development.
Putting greens with poor drainage, excessive thatch and shade are more likely to have problems with yellow patch. Excessive applications (>0.25 lb N/1,000 sq. ft.) of water-soluble nitrogen (WSN) should be avoided in the spring and have been shown to encourage disease development. Springtime nitrogen can be applied as a slow release fertilizer and should not exceed 0.25 lb N/1,000 sq. ft.
Preventative fungicide applications are the most effective means for controlling yellow patch, especially if yellow patch has been a problem in the past. Fungicides from the strobilurin, SDHI (flutolanil), and DMI classes are effective choices for control and more information on which active ingredients are labeled for yellow patch can be found here. Curative fungicide applications will prevent further infection, however, turfgrass recovery is dependent on favorable growing conditions. Since the pathogen is active during very specific environmental conditions, the best course of action for sites with adequate drainage and sunlight is to allow warmer temperatures and sunlight to aid in turfgrass recovery.
If you have questions about fungicide selections for yellow patch control, please contact the UMass Turfgrass Pathology Lab (firstname.lastname@example.org or 413-577-3303). If you need help identifying yellow patch, submit a sample to the UMass Extension Plant Diagnostic Lab.