What Is Take-All Root Rot?

Is your once-vibrant lawn looking a little worse for wear? Are patches of yellow or brown grass spreading, despite your best watering and fertilizing efforts? You might be dealing with Take-All Root Rot (TARR), a common yet frustrating fungal disease that can wreak havoc on your turf.

TARR is caused by a soil-borne fungus called Gaeumannomyces graminis var. graminis. This fungus attacks the roots of your grass, hindering its ability to absorb water and nutrients. The disease is particularly problematic in warm, humid climates where turfgrass is commonly grown. 

Identifying Take-All Root Rot

Take-All Root Rot manifests visually with several distinctive symptoms that alert homeowners to its presence. Initially, grass blades exhibit a yellowing or bronzing coloration, which gradually leads to the thinning of the turf. As the disease progresses, affected areas appear as irregular, discolored patches scattered across the lawn. Upon closer inspection, the roots of the infected grass turn dark, brittle, and decayed, contrasting sharply with the healthy, white, and firm roots of unaffected grass. 

In advanced stages, the grass may wilt and die, leaving conspicuous bare patches that disrupt the uniformity of the lawn. This combination of discoloration, thinning, and root decay is indicative of TARR.

The Differences Between Take-All Root Rot & Large Patch

Large patch (pictured above) is one of the more common lawn diseases in our area, so it is important to know the difference between it and TARR, as they cause different types of damage and must be dealt with in specific ways. The most important thing to remember is that large patch weakens lawns by infecting the grass blades, while TARR infects the roots of grass and is much harder to treat. Both diseases result in weakened lawns, but you must know which part of the grass is infected in order to remedy the situation, and the first step is learning how to spot the differences. 

Large Patch:

• Disease Type: Foliar disease that does not attack the crowns or roots of grass. 
• Patch Shape and Color: Circular or irregular patches of dead grass, often with a distinctive yellow or orange halo at the outer edge.
• Grass Condition: Grass within the patches may appear sunken, matted, and can easily be pulled up.
• Spread Pattern: Patches can expand rapidly, especially during cool, wet conditions.

Take-All Root Rot:

• Disease Type: Root disease that kills roots of grass and causes them to blacken. 
• Patch Shape and Color: Irregular patches of yellowing or bronzing grass blades, without a distinctive halo.
• Grass Condition: Thinning turf with grass blades that turn from yellow to brown. Grass does not easily pull up, but the roots are dark, brittle, and decayed.
• Spread Pattern: Affected areas may appear scattered, with patches varying in size and shape.

Conditions That Cause Take-All Root Rot

TARR is particularly prevalent in specific environmental conditions that favor the growth and spread of the TARR fungus. Take-All Root Rot thrives in the thatch layer of your lawn, and many factors cause thatch to accumulate to unhealthy levels. Understanding these conditions can help homeowners and lawn care enthusiasts take preventive measures to protect their lawns.

• Warm, Humid Climates: TARR thrives in environments with temperatures ranging from 60°F to 85°F and high humidity levels.
• Alkaline Soils: Soils with a pH above 6.5 create favorable conditions for the fungus.
• High Soil Moisture: Excessive soil moisture and poor drainage contribute to the development and spread of the disease.
• Grass Species Susceptibility: Certain turfgrass species, such as St. Augustinegrass, Bermuda grass, and Zoysia grass, are more prone to TARR.
• Soil Compaction: Compacted soils impede proper root growth and drainage, making the lawn more susceptible to fungal infection.
• Stress Factors: Lawns under stress from drought, improper fertilization, or mowing practices are more vulnerable to TARR.

How Take All Root Rot Spreads

Take-All Root Rot primarily spreads through the stolons and rhizomes of affected turfgrass. Stolons are above-ground runners, while rhizomes are underground stems; both are integral parts of grass that facilitate vegetative propagation. Gaeumannomyces graminis var. graminis infiltrates these structures, allowing the disease to move from one plant to another as the stolons and rhizomes grow and intertwine with healthy grass. The disease's spread is facilitated by the way the fungus attacks the root system, causing significant root decay. This root damage impairs the grass's ability to absorb water and nutrients, leading to weakened plants that are more susceptible to further fungal invasion through their interconnected root networks.

This mode of transmission is somewhat unique because, unlike many other lawn diseases, Take-All Root Rot is not commonly spread by lawn mowers, foot traffic, or physical transfer of infected material. Instead, the disease primarily relies on the natural growth patterns of the grass itself, spreading insidiously through the roots and vegetative structures. This makes it particularly challenging to control once established, as the fungus can continue to move through the underground network of stolons and rhizomes, often undetected until significant damage has occurred. Effective management requires targeting the root zone and addressing environmental conditions that favor the fungus, making early identification and preventive measures crucial in protecting the lawn from this destructive disease.

Treating Take-All Root Rot

Proper Irrigation:

• Water deeply but infrequently to encourage deep root growth.
• Avoid overwatering and ensure proper drainage to prevent waterlogging.
• Water early in the day to allow the grass to dry before nightfall.

Mowing Practices:

• Maintain an appropriate mowing height for your grass species to reduce stress.
• Keep mower blades sharp to ensure clean cuts and minimize damage to the grass.
• Avoid mowing when the grass is wet to prevent further stress and potential disease spread.

Soil Testing and Amendment:

• Regularly test soil pH and nutrient levels to ensure optimal growing conditions.
• Lower soil pH if it is above 6.5 by applying sulfur or using acidifying fertilizers.
• Apply balanced fertilizers based on soil test results, avoiding excessive nitrogen.

Aeration:

• Aerate the lawn regularly to improve soil drainage and reduce compaction.
• Aeration helps promote healthy root growth and increases oxygen availability to the roots.
• Thatch harbors the TARR fungus, and aeration is one of the best ways to prevent thatch. 

Fungicide Application:

• Use fungicides containing active ingredients like azoxystrobin, propiconazole, or thiophanate-methyl.
• Apply fungicides preventively or at the first sign of disease according to label instructions.
• Consider using biological fungicides containing beneficial fungi or bacteria.

Stress Reduction:

• Provide adequate fertilization to maintain healthy grass growth, following soil test recommendations.
• Avoid applying herbicides during periods of active disease to reduce stress on the lawn.
• Ensure proper sunlight exposure by trimming overhanging trees or shrubs that may create shaded, humid conditions.

Using Fungicides To Fight Take-All Root Rot

When Take-All Root Rot becomes severe, treating it with fungicides is crucial to prevent further damage and facilitate lawn recovery. Fungicides play an essential role in halting the spread of the fungus and protecting unaffected areas of the lawn. The most effective fungicides for treating Take-All Root Rot include those containing azoxystrobin, propiconazole, and thiophanate-methyl. These active ingredients target the fungus throughout various stages and provide both curative and preventive action. 

For the most effective and safe applications of these products, call a professional landscaping company with the equipment and knowledge needed to keep lawn disease off your property for good. Call Pro Outdoor Landscape Management today for more information.