Lawn Diseases to Look For During The Winter Months
Even during the cooler months, it’s important to understand the care your lawn needs. The two primary turf problems during the winter months are brown patch fungus and winter annual broadleaf weeds. Both of these problems can be greatly affected by excessive soil moisture. Here are some other common fungus and diseases to be aware of during the winter months.
DISEASE: Large Patch and Brown Patch diseases of turfgrass
PATHOGEN: Rhizoctonia solani
HOSTS: Warm- and cool-season turfgrasses
Rhizoctonia solani is a pathogen that causes Large Patch disease in warm season turfgrass species and Brown Patch disease in cool season turfgrass species.
Large Patch and Brown Patch are the same disease caused by the same fungus but have different names depending on the type of grass.
Large Patch fungus is very common in warm season turf such as in St. Augustine, Centipede, Bermuda and Zoysiagrass. Shade tolerant varieties of St. Augustine such as Seville are often the most severely affected.
Brown Patch fungus is commonly found in cool season turf such as bentgrasses, bluegrasses, fescues, and ryegrasses.
The fungus affects the base of the leaf sheath where the blade attaches to a stem of the plant.
The easiest way to distinguish Large and Brown Patch from other causes of turf decline is to pull on the leaf blade. Leaf blades affected will detach very easily from the stolon and slide out of the sheath. Further inspection of the base of the blade will show dark water soaked tissue.
The pathogen causes symptoms that begin as spots and become larger as the disease spreads. It will cause damage to the leaves, but does not harm the stems or roots, thus the turfgrass in the center will begin to repair, sometimes resulting in a donut-like appearance.
This fungus develops most rapidly when the air temperatures are below 80° and free moisture is present on the leaf. Infection is triggered by rainfall, excessive irrigation or extended periods of high humidity resulting in the leaf canopy being continually wet for 48 hours or more.
These conditions occur most often and for a longer duration in the fall and in the late winter/early spring. High levels of readily available nitrogen will also increase the severity of the disease. Fungal activity generally stops when air temperatures reach 90°; therefore it is normally not active during the summer.
The disease triangle is a concept that helps us understand what is needed for a disease to be active. The disease triangle includes the following:
1. Host: The host is the turfgrass.
2. Pathogen: Rhizoctonia solani.
3. Conducive Conditions: Excessive moisture and plant stress are examples of conducive conditions.
Rhizoctonia solani is a soil-borne pathogen and can cause disease when conducive conditions are present. Mitigating conducive conditions such as extended leaf wetness and applying a fungicide will suspend the fungal activity and allow the turfgrass to recover. As seasonal conditions change, the fungal activity will stop due to lack of conducive conditions. Our team members apply fungicides accordingly and irrigate lightly into the soil so the material will enter the plant through the roots and move to the site of attack. A follow up in 21-28 days is necessary to ensure recovery.
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