When spring arrives early and temperatures stay elevated through the summer like they did this year, summer patch (Magnaporthiopsis poae) has more opportunity to establish itself and damage Poa annua and Kentucky bluegrass playing surfaces. Warm and sunny conditions in April had many celebrating during aeration, but the extra weeks with warmer soil temperatures brought increased disease pressure later in the year. Very few superintendents in the Northwest have much experience with summer patch due to its rarity in this region – and even fewer operate preventative spray programs that would protect against it. The resulting damage some courses experienced this year was severe. The pathogen infects crowns and roots when the soils warm up in late spring, then symptoms explode in midsummer when hot periods follow rain, high humidity, or even smoke events that hold moisture near the canopy. Reducing the moisture would be helpful, but shutting off irrigation isn’t an option in the middle of summer. The result is wilt, thinning and discolored patches that are easy to mistake for drought or heat stress.

Accurate identification is tough because the symptoms mirror other summer problems. As the disease attacks turf from the bottom up, the visible symptoms can appear to be anthracnose (Colletotrichum cereale) or drought stress. Initial reactions from staff are often to apply more water to infected areas, which is not what is needed. Positive diagnosis often requires a lab sample, and curative control is unreliable. The most dependable programs are preventive, and include various chemistries that start in early spring and continue through summer. Looking ahead to next year, if you want to minimize the risk of summer patch damage, a solid preventative spray program is the most cost-effective defense. Cultural practices like topdressing, venting and verticutting can be a larger budget impact, but combined with precision water management – especially during the hottest weeks – will help bolster a less disease prone growing environment. Below is some information to help you plan for managing this increasingly problematic pest.

When is summer patch active?

• Root/crown infection begins in late spring when soil temperatures at the 2-inch depth reach approximately 65 F for several consecutive days.
• Symptoms typically flare in midsummer when the temperature is 82 F and above, especially after rainy or humid spells.
• Rootzone temperatures above 75 F accelerate decline.

Look out for look-alikes

• Localized dry spot (LDS), heat/drought stress, anthracnose and necrotic ring spot (Ophiosphaerella korrae) can all exhibit similar symptoms to summer patch – i.e., crescent- and ring-shaped patches of wilting turf that can coalesce into larger damaged areas.
• Because of these look-alikes, lab or microscope confirmation of summer patch is often needed.

Chemical control

• Use preventive fungicides, rotate FRAC codes and water-in per the label.
• In late spring before peak temperatures, use propiconazole (DMI) and consider thiophanate methyl at high label rates.
• During early to midsummer, use azoxystrobin or other QoIs; repeat on three- to four-week intervals where disease pressure history is severe.
• Combination products (e.g., QoI + DMI) provide broad-spectrum protection. Be sure to maintain adequate carrier volume and apply light post-application irrigation to move the active ingredient to crowns and upper roots.
• Do not pair DMI fungicides with plant growth regulators (e.g., paclobutrazol or flurprimidol) as the combination can oversuppress growth and increase phytotoxic risks in summer.

Long-term planning

• Long-term goals should be to build strong roots and reduce organic matter in the rootzone.
• Topdress and aerify/vent routinely to reduce surface organic matter and improve infiltration and gas exchange.
• Improve air movement and drainage where necessary.
• Slightly raise heights of cut on surfaces that are prone to infection.
  
  

Summer patch caught some superintendents off guard this year with more damage from the disease than we’ve seen in the past. Difficulty diagnosing the issue coupled with poor curative measures makes preventative action and forward planning paramount. With changing weather patterns and data trends showing increasing summer temperatures, we can expect summer patch to be an issue again in the future. As the saying goes: “An ounce of prevention is worth a pound of cure.”

West Region Agronomists:

Brian Whitlark, regional director, West Region – bwhitlark@usga.org

Ross Niewola, agronomist – rniewola@usga.org

Information on the USGA’s Course Consulting Service

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