Pennsylvania Turfgrass – Travis R. Russell and John E. Kaminski, Ph.D.
This year is likely one that we all are going to want to forget. While our undergrads were on spring break and the two-year students were at TPC Sawgrass volunteering for The Players Championship, Penn State decided to shut down campus for the remainder of the semester. Faculty and students scrambled to shift to online learning while others were stuck at home waiting for their internships to begin.
On March 19th, Governor Wolf ordered all non-life-sustaining business to close across the state. Turfgrass managers scrambled to get exemptions to at least be able to maintain their turfgrass during the shutdown. On May 1st, golf courses throughout the state of Pennsylvania were reopened for play. We are all now familiar with “pool noodles” in the cups, no rakes in the bunkers, no touching of the pins, and four golf carts per foursome. Things looked very different from a golf perspective.
From a “turf” perspective, things also started out a little slow. Bentgrass was slow to wake up and Poa seedheads peaked right around the time golf courses were opening. These were all par for the course and not atypical in any given year. Throughout May and June, golf course fairways were in some of the best shape we’ve seen, but turf health was about to go south.
Many areas had limited rainfall. State College had less than 1” of rain total during the months of May, June and July. That also coincided with periods of extreme temperatures in June and July. The need for supplemental irrigation to keep turf alive combined with high temperatures and relative humidity resulted in a series of disease outbreaks in the middle of the summer.
Bacterial wilt is an uncommon disease of annual bluegrass. Bacterial wilt was diagnosed several times in our lab this year from multiple golf courses throughout the northeast region. In fact, a severe bacterial wilt outbreak occurred on a young annual bluegrass green at our research facility in early June (Figure 1). The disease was initially observed as small, speckled necrotic spots on the green in early to mid-June that quickly coalesced into larger diffuse areas of turf loss by early July.
Control of bacterial wilt is difficult since chemical options are not efficient or practical with products having to be applied after every mowing. Instead, turfgrass managers must designate a mower specific only to the infected turfgrass surfaces and mow in the afternoon when turf is dry to limit spread to healthy areas of turf and to avoid abrasive cultural practices while disease is active.
Anthracnose (Figure 2) is chronic disease on annual bluegrass green during the summer. Symptoms include yellow to orange spots of infected Poa but expand into a general thinning of highly infected areas. Golf course superintendents can easily identify this disease by looking for blackening at the crown and black fungal structures (i.e. setae) on individual leaves. Although we diagnosed samples from other region in June, anthracnose severity began to increase in the first few weeks of July on our research putting green. By the end of July into early August, anthracnose was uniformly distributed throughout the green.
Preventive fungicide programs are essential to effectively control anthracnose. In addition, minimizing physiological stress is recommended to slow disease intensity. Maintaining adequate fertilization and irrigation will significantly limit physiological stress that can increase disease severity. Increasing mowing height is a critical mitigation strategy but long-term cultural control strategies of reducing organic matter thatch development with regular aerification and routine topdressing when disease is not active will significantly help in combatting the disease.
Brown patch (Figure 3), caused by the pathogen Rhizoctonia solani, can be problematic on most turfgrasses including those grown on golf course putting greens, tees and fairways, but also in the rough where tall fescue has become a more utilized species. Brown patch generally has a narrow window of activity in central PA but can be a more common problem in other areas where prolonged warm temperatures and high relative humidity are present. In 2020, however, the extended hot and humid conditions in State College resulted in prolonged brown patch activity from late June that continued into August.
Maintaining adequate, but not excessive nitrogen fertility and proper irrigation strategies can limit the occurrence of brown patch. Avoiding long periods of leaf wetness through early morning dew removal significantly reduces the duration of leaf wetness which is favorable for disease development. Several fungicides are available for preventive and curative control of brown patch.
Pythium blight is always a fear for turfgrass managers when intense heat waves roll through in the peak of summer across the state. The progression of Pythium blight is often manifested by cottony mycelial growth causing rapid blighting that leaves large areas of turf bare in a matter of days. This year, the unusually hot and humid conditions consistent throughout July allowed for Pythium blight to strike at a moment’s notice over this long stretch in the warmest part of the growing season. Outbreaks observed in our lab were generally from situations where turf was irrigated frequently due to the lack of rainfall. The excessive moisture combined with high temperatures resulted in rapid death.
Limiting excessive moisture through proper irrigation and drainage practices is important in reducing conditions favorable for the Pythium pathogen. Preventative fungicide applications are a must when environmental conditions are favorable for growth of the pathogen to limit Pythium blight outbreaks and subsequent turfgrass loss.
Pythium patch (Figure 5) is currently an undescribed and unique disease of annual bluegrass putting greens. Our lab is currently investigating the pathogen to fully understand its biology as well as the epidemiology of the disease. This disease emerges in patches less than a foot in diameter and progresses slowly over time. The pathogen can completely kill turfgrass within the patch and often has a thin, yellow ring of turf at the patch borders. Symptoms mimic summer patch where unaffected creeping bentgrass fills in patches where annual bluegrass has been killed. The disease has been found in a dozen or more states and emerged this year on a young annual bluegrass putting green at the Valentine Turfgrass Research Facility in early July and continued into August, allowing us to collect valuable data on the disease.
Control strategies are currently being investigated, but ensuring proper nutrition, irrigation, and drainage is important to minimizing suitable conditions for favorable infection and disease development. Fungicides typically used to control Pythium diseases are currently recommended during the summer months. Reliance on fosetyl-Al as your sole Pythium fungicide should be avoided as anecdotal reports suggest it to be less effective. The benefits of fosetyl-Al as a Pythium blight control and its enhanced summer stress relief warrant its use, but other more traditional Pythium fungicides should be incorporated into the overall program.
Summer patch (Figure 6) has not appeared at Valentine in at least 10 years, but that changed in 2020. Summer patch is a severe root pathogen that causes disease of annual bluegrass and Kentucky bluegrass. Initial symptoms include small circular patches that ultimately can increase up to 1’ or more in diameter. Grasses and weeds that are not susceptible to the pathogen often fill in infected areas creating a “frog eye” appearance to the patches.
Symptoms appeared in our anthracnose fungicide trials in late July and became severe in August. Fungicide control programs need to be initiated in the spring with the general rule of thumb being to make the first application when soil temperatures at a 2” depth at 2:00-3:00pm reach 65F for several consecutive days. A tank mix of a DMI and QoI are generally considered to be most effective but must be reapplied every 21 to 28 days through the summer months.
Despite this being a banner year for turfgrass diseases in PA, the main disease threat that we annually contend with, dollar spot (Figure 7), had a slow start in central PA due to dry conditions and high temperatures. Warm days and cool nights in early August, however, resulted in a dramatic increase in dollar spot and are setting up for a severe fall season for managing this disease.
Dollar spot can be minimized culturally through adequate nitrogen fertility, maintaining sufficient soil moisture and limiting lead wetness periods during periods of favorable environmental conditions. Preventative fungicide applications are often necessary to completely control the disease in lower cut turfgrass. With the potential for a severe fall dollar spot season, turfgrass managers should be cautious not to let their guard down in September and maybe even into October.
Gray Leaf Spot
Although at the time of writing this article gray leaf spot has not been identified in the state, turfgrass managers should always be wary of its appearance in late summer and early fall. Initial reports from the southeastern US suggest that this could be a severe year for the disease. Recent reports of gray leaf spot causing severe outbreaks on tall fescue in our region means that it’s not only stands of perennial ryegrass that should be scouted for the disease.
Although 2020 will be most remembered by many for the impact COVID-19 had on our lives, turf pathologists will likely remember this as one of the most severe disease seasons on record. The presence of such a diverse set of pathogens and significant disease outbreaks will make for a year that we will soon not forget.