Diseases push on the throttle; 1st observation of brown patch on tall fescue; annual bluegrass weevil damage on bentgrass surrounds; foliar anthracnose and localized dry spot on putting greens.
* I need a moment to recognize the passing of David Riedman, superintendent at Woodland Country Club in Carmel, IN. David was a great colleague and cooperator, and one of the very first to contact and invite me to his course after moving to Purdue. In a very short time, he became a valued mentor. Thank you David, and rest in peace my friend.*
Weather
Current morning jacket weather shouldn’t disguise the overall warm May that has jump started plants and pathogens alike this late spring. By all accounts, the region is still running 2-3 weeks ahead of normal. Here in W. Lafayette, GDD50 accumulation is 200+ above our standing this time last year (MSU GDD Tracker website), and most areas are 5+ degrees above normal average temperature for the month. Keeping an eye specifically on the minimum temperature is also useful concerning disease activity, and the region is also 5 – 8 degrees above average in this measure.
Rainfall hasn’t been quite as pervasive in May as in April, but race day’s large rainfall event (1.5” + in areas) will likely push many above average for the month. Indy officially sits at 5.24”, about an inch above average, with points south receiving even higher amounts. Fort Wayne and northern IN have escaped the brunt of most storms and are right about on average.
Forecasts indicate a jet stream dip this week resulting in cooler conditions for the region to close out May with a return to warmer temperatures in the first week of June. The rest of May also is expected to be drier, with a return to widespread chances for rainfall to start June. Disease pressure will likely follow this same pattern, with a quick wane this week followed by an early summer ramp up.
Lawns: Brown Patch on Tall Fescue Arrives
Higher than normal nighttime temperatures resulted in characteristic brown patch lesions observed last week on our tall fescue research plots at the Daniel Turfgrass Research Center. These lesions are associated with some marginal thinning in patches and appear as a beige to bleached interior with a dark brown margin scalloped across the leaf blade. Brown patch caused by Rhizoctonia solani is perhaps the Achilles heel pest problem that affects turf type tall fescue perennially and causes the most grief on home lawns. In our testing, Ascernity fungicide has been extremely effective in controlling this disease, however, use is limited to golf courses and the product can’t be applied in residential areas or sports fields. On home lawns, azoxystrobin (Heritage, Scotts Disease EX) and pyraclostrobin (Insignia, Pillar) are commonly suggested fungicides.
Our knowledge in mitigating this disease without fungicides has changed considerably in the last decade. Gone should be the notion that any nitrogen during the summer will spur ferocious brown patch outbreaks. Thanks to work by Dr. Jim Kerns, and Purdue’s team of Drs. Jada Powlen and Cale Bigelow, nitrogen applications have been shown to perhaps reduce brown patch in hungry tall fescue rather than spark this disease. Regarding tall fescue and most turfgrasses, it’s important to realize that nitrogen is often limiting. Nitrogen is mobile and moves to the youngest leaf which we habitually prune or mow off. While mulching type mowers may help to recycle this nitrogen, the process still takes time which an actively growing lawn might not have. All of this to say that a low dose of nitrogen (0.25-0.5 lb N/1000 sq ft) once or twice during the summer applied with care and intention will do more good than harm to a lawn.
As is the case for most foliar diseases, shade, dew, wet leaf blades and high humidity are the allies of a strong brown patch epidemic. Brown patch will form more readily in a tree-filled space or around structures that block the morning sun. For most, lawn irrigation shouldn’t have be running yet, but when needed, irrigating at dusk is a sure-fire way to get the leaf wetness and disease party started. Another oft overlooked issue is with grass clippings. If left in clumps over the lawn canopy, they act as a plastic bag over the turfgrass, keeping humidity and moisture in. The brown patch pathogen will take this opportunity to infect and cause severe disease on a plant that is already hamstrung with a lack of light. To mitigate this, mow as often as possible to reduce clumping and be mindful by simply using a blower to disperse and spread large clumps.
Last but not least, establishing a resistant cultivar from the outset or through overseeding is the best, most long-term control strategy. For more information on brown patch control in tall fescue, see this recent article in the USGA Green Section Record.
Pythium root rot and summer patch prevention
Throughout the state, two-inch soil temperatures are well in the range for preventive fungicide applications for summer patch and Pythium root rot (for current soil temperature information for Indiana, click here.) Summer patch should be prevented in high value Kentucky bluegrass sports fields and lawns that have had a history of the disease. On sports fields, fertilization with ammonium sulfate and/or manganese sulfate is recommended to supplement control. Summer patch has also been observed frequently attacking samples of bentgrass and Poa annua putting greens. A watered in application of a strobilurin, DMI fungicide or combination product may also be warranted, and must be watered in with at least 0.2 – 0.25” of post application irrigation or rainfall to be effective. On poorly draining putting greens, restricting AMS or manganese sulfate use may be best to not spur black layer formation.
Speaking of poorly draining, the time is also past due to apply preventive applications for Pythium root diseases on golf putting greens. Picarbutrazox (Serata) and cyazofamid (Segway) are suggested as the two heaviest hitters and should be the backbone for Pythium root disease control (both root rot (various spp.) and root dysfunction (mostly caused by Pythium volutum)). As with all fungicides targeting soilborne diseases, applications should be watered in with at least 0.125” and preferably closer to 0.2 – 0.25” of post application irrigation.
Golf: Annual Bluegrass Weevil Damage & Need for Scouting
A sample from a bentgrass/Poa collar with considerable damage from annual bluegrass weevil was submitted from south central IN to the Purdue Plant & Pest Diagnostic Lab last week. The superintendent stated these areas had struggled for the last few years and surmised this could’ve been the underlying issue. Our resident turfgrass entomologist, Dr. Doug Richmond, took over the case and recommended treatment options based on the stage(s) of insect development. To learn more about this increasingly important pest problem, see this recent article in the USGA Green Section Record.
Localized Dry Spot on Putting Greens & Fairways
The first instances of localized dry spot have taken hold at the research farm and in two submitted samples last week. Localized dry spot (LDS) is caused by the exudates and by products of microorganisms breaking down thatch and organic matter. These hydrophobic organic acids coat soil particles and repel water, creating preferential flow patterns in the soil matrix and robbing affected plants of needed moisture. To diagnose this issue, a TDR can be employed for evidence, but using a soil sampler (preferably a soil profiler) or large knife to excise an affected portion of turf and soil can provide the real proof. Use a squeeze bulb dropper or carefully managed straw to place water droplets along the soil matrix at different depths. Droplets will not enter the soil where hydrophobicity has set up, with one of my records being five days with no infiltration in a fairy ring/LDS affected soil. A myriad of soil surfactants (aka wetting agents) are on the market targeting LDS control.
Foliar anthracnose damage on bentgrass and annual bluegrass
Last but not least, anthracnose season arrived early last week with foliar anthracnose on untreated plots on our research green and several samples arriving at the PPDL. Anthracnose caused by Colletotrichum cereale can take two forms, foliar and as a basal rot. The foliar form being observed now is characterized by a bronze leaf appearance, with the disease mostly attacking older leaf blades and leaving the youngest leaf and crown intact. Characteristic hair-like setae accompany spore producing acervuli on the leaf surface with numerous club or peg-shaped appressoria dotting the leaf sheath. Foliar symptoms often precede the darker, whole plant affecting basal rot disease form. The pathogen dives down past the leaf sheath and rots the crown or base of the plant, turning it a dark brown to black color.
Turfgrass leaves have a short life cycle, being produced and dying within a 1-2 month span. This provides ample nutrition and habitat for pathogens like anthracnose that can survive as both saprophytes (living on dead or decaying organic matter) and pathogens. This also serves as a reason for anthracnose to be so closely related to plant stress, since as the leaves more rapidly decay and degrade the pathogen population and inoculum level summarily increases with the added food source. The larger pathogen population soon switches gears to overwhelm and attack living plant tissues. As mentioned previously, low nitrogen levels also play a crucial role in anthracnose development as nitrogen moved to the younger leaf tissue leaves the older leaves more susceptible to infection.
A sample from a bentgrass fairway late last week was the first time I have observed considerable foliar anthracnose infection on higher cut turfgrass. These fairways had extremely low nitrogen applied this season, high use rates of plant growth regulators, harsher pre-emergent herbicide application on an older bentgrass variety and were mowed below 0.5”. All of these practices aimed to produce a faster and firmer playing surface, whether on fairways or greens, play right into the hands of creating an anthracnose epidemic. In these ripe conditions, fungicide use would be needed and may not last the expected application interval.
Due to its biology and aptitude for spore production, fungicide resistance development in anthracnose pathogen populations can occur quickly. Resistance to the benzimidazole fungicide class (thiophanate-methyl) is commonplace and several populations are also resistant to the QoI (strobilurin) and/or DMI fungicide classes. Resistance management by rotating fungicide mode of action and tank-mixing a contact fungicide (i.e. chlorothalonil or fluazinam) with a systemic in curative applications is suggested to mitigate fungicide resistance development. A list of best management practices for anthracnose control on annual bluegrass has been developed through research at Rutgers University.
Purdue Turfgrass and Landscape Field Day – Tuesday, July 16th
The Purdue Turf and Landscape Field Day is an annual one-day event with the objective of providing professional turf and landscape managers exposure and educational opportunities with the latest research and technical resources. Field Day features research tours, talks on current topics, and a tradeshow with over 40 exhibitors displaying equipment, turf, and landscape products.
Turfgrass Pathology Program Impact Survey
Follow this link or scan QR code above to access the survey.
Lee Miller
Extension Turfgrass Pathologist – Purdue University
Follow on Twitter: @purdueturfpath