Curvularia and Ectotrophic Root Infecting ( ETRI ) fungi have been identified as the culprits. So what do we know about these pathogens?

Curvularia is a common fungus which can be isolated from dead and decomposing leaf tissue found on apparently healthy putting green turf. For nearly five decades turf scientists have debated whether or not this fungus is a saprophyte (i.e., living on only dead plant material) or a weak to strong pathogen (i.e., infecting and causing injury to living plant tissue).

Recently the Japanese have elevated Curvularia as a true pathogen-giving this leaf blighting fungus the name “Dog Footprint” disease. The disease name represents the primary diseased leaf pattern as seen in Japan. Unfortunately, here in the U.S. this leaf pathogen takes on many more symptom patterns than just the “Dog Footprint” pattern. Depending upon the time of year, turfgrass species, and level of nitrogen fertility Curvularia infected leaf tissue can take on one of three different colors and five different overall patterns. Along the Gulf Coast, Curvularia has been found to be active as late as early January 2003.
ETRI represents a wide range of root infecting fungi which are soilborne in habitat. Such diseases as “Spring Dead Spot”, “Bermudagrass Decline”, “Take All Patch” and “Necrotic Ring Spot” are all caused by members of this group. ETRI fungi are found growing on the surface of stolons, rhizomes, roots, and rootlets and if left untreated will eventually send infection structures into these tissues. Under low power of a dissection scope one can often see darkened areas of plant tissue at the junction of roots and rootlets.

Turf infected with ETRI normally exhibits irregular circular areas of chlorotic to brown leaf tissue. Sometimes the disease pattern includes a brown outer ring. Often one can see a growth stimulation pattern of overseeds matching the outer ring of an ETRI infected area. And, in the case of Seashore Paspalum greens type cultivars, ETRI infection in the stolon mat takes on the appearance of jet black irregular spots several inches in diameter.

So which comes first, Curvularia or ETRI? Do ETRI weakened roots place stress on leaf tissue which leads to Curvularia leaf blighting? Our observations indicate that a Curvularia/ETRI disease cycling takes place- but in no specific order. And, to make matters worse, when both diseases are active at the same time, greater confusion can take place when trying to use visual symptoms only to diagnose the problem.

Curvularia/ ETRI Control Strategies:
Turfgrass genetics. So far we have found these diseases on the old standard bermudagrasses such as “328” and “Tifdwarf”, all the major used bermudagrass ultradwarfs, along with the Seashore Paspalums. While we have not had the sample base to comment on the bentgrasses, we suspect they have a similar problem. Pushing any variety to its limit- by lowering of mowing height- tends to increase disease incidence and severity.

Nutrition: Dr. Larry Stowell of Pace Consulting ( www.pace-ptri.com) points out the need to keep manganese (Mn) levels up. Mn stimulates the production of antimicrobial substances in the roots which can slow the ETRI infection process.

Fungicides: For Curvularia there are a number of foliar applied fungicides which give control. Fungicides labeled to control Bipolaris (formerly Helminthosporium Leaf Blight and Melting Out) normally will control Curvularia. For ETRI control one must use a systemic fungicide watered in so that the active ingredient reaches the infected tissue. In order to achieve the best results the golf course superintendent is encouraged to try side-by-side applications of several systemics to determine which works best. You can not apply fungicides for both Curvularia and ETRI control as a tank mix because of the no watering in vs. watering in requirement. Once you have been diagnosed with these diseases you will need to consider switching to a true preventive program with a spray interval of a week to 10 days for Curvularia control and a 2-3 weeks for ETRI control.

How much was weather a factor in the widespread outbreaks of Cuvularia and ETRI this past fall? In southern Alabama along the Gulf Coast the average nighttime (low) temperature for September and October was 5F and 10F higher than average. Rainfall for the same period of time was over 200% of normal. While unusual weather conditions may have been responsible for the initiation of the diseases it does not explain their persistence into late fall and winter.

So what can golf courses having had the diseases this fall expect this spring when their primary putting green turf comes out of dormancy? We have taken samples of diseased turf and have broken dormancy using a growth chamber to provide long days and high day and nighttime temperatures. Samples having been diseased and left untreated going into dormancy have gone on to be diseased in our growth chamber environment. Most, but not all, of the samples having been diseased but fungicide treated came out of dormancy healthy. We have, in effect, developed an EARLY WARNING technique to give superintendents advanced warning of pending disease problems come spring transition. For more information on our EARLY WARNING program please call 251-986 6240 or e-mail us at: mjhealy@gulftel.com. We also have jpeg color images of Curvularia and ETRI symptoms on putting green turf available via the Internet.