Verdure: Anthracnose can go play in the sand

August 2023 | Mike Fidanza, Ph.D.

The “Mount Rushmore of Turfgrass Pathology” most likely would include professor Lawrence Dickinson (1888-1965) and J. Drew Smith (1922-2003), Houston Couch (1924-2004) and Noel Jackson (1931-2018). Of note, no current living turfgrass pathologists are eligible. Anthracnose is a serious and feared turfgrass disease that those plant pathologists studied during their careers. Anthracnose is caused by the fungal pathogen Colletotrichum cereale, and this disease is particularly troublesome on annual bluegrass (Poa annua) within those “bent/Poa” mixed-stand putting greens.

Couch referred to anthracnose disease of turfgrass as a “senectopathic disorder,” implying the pathogen’s preference to infect senescing leaf tissue. With senescence, plant tissues stop growing due to age and from environmental and mechanical-induced stresses. Anthracnose in the Mid-Atlantic U.S. was severe in the late 1990s and early 2000s when putting green mowing heights were getting lower and the desire was for faster green speeds. USGA Green Section agronomist Stan Zontek (1949-2012) would often say, “Anthracnose would tell us just how low we can mow those greens.” At that time, questions were asked about foot traffic, along with potential abrasion of leaf tissues from sand topdressing on those putting greens, thus contributing to abiotic stress and predisposing annual bluegrass to anthracnose.

Let’s revisit the Rutgers University investigation on the effects of foot traffic and sand topdressing on anthracnose (previously reviewed in Verdure in May 2016). The two-year study was conducted on an annual bluegrass putting green, which had already been established from soil cores removed from an existing mature annual bluegrass green in central New Jersey. The putting green was mowed daily at 0.125 inch (3.2 millimeter) and received a maintenance program of foliar nitrogen, plant growth regulator (trinexapac-ethyl), fungicides to control other diseases but not effect anthracnose, and herbicides to control weeds and creeping bentgrass encroachment. The site was previously inoculated with C. cereale to ensure a reliable anthracnose epidemic.

Experimental treatments consisted of foot traffic with sand topdressing, foot traffic only, sand only, and no traffic or sand (i.e., a non-treated or “check” treatment) and were randomized and replicated four times. Sand was applied to the main plots measuring 3.2 feet by 12.1 feet (1 meter by 3.7 meters), and individual sub-plots subjected to foot traffic were 3.2 feet by 6.2 feet (1 meter by 1.9 meters). Foot traffic consisted of physically walking on the test plots with golf shoes that had softspikes, at approximately 30 footsteps per square feet (327 footsteps per square meter), which reflects the number of footsteps around a hole on a putting green that receives 200 rounds per day. The foot traffic was delivered daily between 10 a.m. and 1 p.m. from June through September in both years of the study. Sand topdressing consisted of a subangular silica sand delivered as 28 cubic centimeters per square foot (0.3 liters per square meter) every week from May through August in both years of the study. The sand topdressing was incorporated into the putting green surface using a brush.

After two spring and summer seasons, what happened to the anthracnose? The annual bluegrass was still affected by the disease, but there was a noticeable reduction in anthracnose severity in those foot traffic plots with or without sand topdressing. So, all those rounds of golf did not make the anthracnose worse, and perhaps foot traffic — like rolling — is beneficial by “pressing” plant tissues, thus preventing those important meristematic crowns from mower scalping and perhaps improving contact between adventitious roots and the soil (i.e., improved plant health via increased nutrient and water uptake). Sand topdressing alone initially increased anthracnose severity, but later in the summer decreased anthracnose severity, with speculation that perhaps sand also was protecting those plant tissues and crowns.

The researchers concluded that weekly sand topdressing in combination with proper mowing, fertilization, raising mowing heights and maintaining adequate soil moisture could potentially reduce fungicide use required to effectively manage anthracnose on those annual bluegrass putting greens. Sand topdressing philosophies and practices certainly merit further discussion at another time. Overall, sustainable or best management practices provide the most effective way to manage anthracnose on annual bluegrass putting greens.

Source: Roberts, J.A., and J.A. Murphy. 2014. Anthracnose disease on annual bluegrass as affected by foot traffic and sand topdressing. Plant Disease 98(10):1321-1325 (https://doi.org/10.1094/PDIS-08-13-0877-RE).

Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 21-year member of GCSAA.