The cold is coming

Features - Lawn Care

While not as intense as other seasons, winter turfgrass diseases can pose a problem on lawns.

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November 7, 2019

I am fortunate enough to receive a monthly communication from a local turfgrass diagnostic laboratory throughout the growing season. For much of the summer, it highlights how many weeks or months we have left of warm, humid, disease-loving weather. Almost as if we are children waiting for the last day of school. Then, all at once in September, there is a green industry sigh of relief that can almost be heard. Does that mean the risk is gone for turfgrass disease? The short answer is no, but the encounters with disease through winter are generally more predictable and less intense than summer.

Disease-causing fungi are largely inactive through winter when temperatures are below freezing. So, while we may classify them as winter disease, the development is more dependent upon our actions in the fall.

The most common winter disease seen in cool-season turfgrass is snow mold and red thread. Both prefer cool, wet conditions. But, contradicting the name, not all snow mold disease requires snow cover for infection. The most common warm-season turfgrass disease is large patch, which becomes most active when soil temperatures fall below 70 degrees Fahrenheit.

The most critical (factor) is unfortunately often out of our control: moisture.”

The winter diseases considered above can largely be influenced by the same cultural practices. The most critical is unfortunately often out of our control: moisture. In many parts of the upper Midwest, folks have experienced record rainfall through the fall, which will enhance disease pressure. In these areas, encourage proper soil drainage and thatch management through aeration.

Fall fertilization is critical for plant maintenance after a stressful summer season. Be cautious with this application as turf can be over-fertilized in fall, leading to overly succulent plants that promote disease.

The most common winter disease seen in cool-season turfgrass is snow mold.
© Maycal | istock

Weed Man Lawn Care utilizes a slow-release nutrient source that limits nutrient release in cold temperatures to help manage growth and disease pressure. Also, be sure choose your rate carefully. Depending on the product, timing and plant species, your application rate should be considerably lower in the fall compared to other times of the year.

Mowing is also in our control. Continue to mow at proper heights through fall until turfgrass growth has ceased. I have heard many suggest the final mowing should be low, often lower than any other time of the year. I have yet to identify the reasoning. However, it is likely that these reduced mowing heights could increase crown exposure to cold temperatures and winds causing winter desiccation.

Disease-causing fungi are largely inactive through winter when temperatures are below freezing. So, while we may classify them as winter disease, the development is more dependent upon our actions in the fall. The most common winter disease seen in cool-season turfgrass is snow mold and red thread.

The final component of lawn preparation for winter is detritus management. Excessive detritus, most commonly leaves, on the turfgrass surface can harbor fungi that cause disease. Removal of this material can be necessary, but where applicable, mulch the detritus into the canopy as it can reduce weed pressure and recycle nutrients.

Proper management of the turfgrass system helps prevent disease, but it doesn’t ensure 100% disease prevention. What we do from here is largely dependent upon the client’s acceptable threshold of damage. I generally don’t suggest chemical treatment to avoid winter disease damage on residential turf as most will recover naturally, but some high-end turfgrass systems may require fungicidal applications. Choose carefully as many products exist on the market with variable control success. Feel free to consult a local turfgrass laboratory or extension agent, which is always a good idea when managing turfgrass disease. L&L

The author is director of operations for Weed Man.