Take-all root rot

What is take-all root rot?

Take-all root rot is caused by Gaeumannomyces graminis and related fungi. UF/IFAS says it is also called bermudagrass decline, and NC State notes recent research ties several closely related organisms to it. The fungus lives on the roots of warm-season grasses, often without harming them, and causes disease when the grass is stressed.

UF/IFAS explains that this is a root disease. Leaves yellow only because the roots are rotting. By the time leaves show symptoms, the fungus has usually been working on the roots for at least two to three weeks. That is why fungicides applied after symptoms show work less well than cultural fixes.

Long rainy periods are the biggest trigger. In Florida, UF/IFAS says it shows up in summer and early fall, when most rain falls. Texas A&M says the fungus is active in fall and winter with plenty of moisture, and symptoms often show in late spring or early summer when heat and dry weather hit. Anything that stresses the lawn, such as scalping, herbicides, too much water or poor drainage, makes it worse.

Symptoms and signs

• Irregular yellow or light green patches from a few inches to a few feet across
• Patches turn brown, thin out and spread outward, sometimes leaving bare ground
• Roots short, black and rotted
• Black spots or rot on stolons and rhizomes
• Stolons pull up easily because the roots have rotted

Take-all root rot identification: what to look for

• Symptoms: Irregular yellow (chlorotic) or light green patches. UF/IFAS gives a few inches to a few feet; NC State gives 4 to 48 inches on golf greens. Older leaves yellow first.
• Symptoms: Roots start thin and off-white with isolated black spots, then become short, black and rotted. Stolons and rhizomes get black lesions and can rot.
• Signs: Under a microscope, dark runner threads and small attachment structures (hyphopodia) on roots and stolons.
• Timing: After long wet spells and stress. NC State gives an ideal soil temperature range of 77 to 86°F for the organisms. Florida sees it most in summer and early fall.

Disease cycle

The fungus lives on and around the roots of warm-season grasses and can be present on healthy turf. NC State notes it can be carried to new sites on sprigs. During long rainy periods or other stress, it invades the roots, stolons and rhizomes and rots them. Leaf symptoms show weeks later, once the root system can no longer support the plant. Patches spread outward through the turf over time.

When to look: Watch St. Augustine and bermuda lawns during and after long rainy stretches. In Florida that is summer and early fall; Texas A&M notes symptoms often appear in late spring or early summer.

Take-all root rot look-alikes

A few things get mixed up with it:

• Brown patch or large patch (Rhizoctonia solani): Texas A&M says leaves of brown-patch-infected grass pull off easily, while take-all leaves do not. The UF/IFAS Indian River County office notes take-all patches are not circular like brown patch.
• White grub damage: Texas A&M notes the stolons lift easily, much like grub damage. Check for grubs in the soil and for black, rotted roots.
• Root-knot nematode or Pythium root rot: NC State says take-all root rot can mimic these. A lab test is needed to tell them apart.

How to manage take-all root rot

Cultural control

• Mow at the correct height and never remove more than one-third of the leaf at once. Do not scalp.
• Balance nitrogen with an equal amount of potassium, using slow-release forms, as UF/IFAS advises.
• UF/IFAS says to avoid nitrate nitrogen and quick-release urea, and its Indian River County office says ammonium forms appear to help.
• Apply manganese sulfate as a foliar feeding, per UF/IFAS.
• Do not lime the lawn, UF/IFAS advises. Texas A&M suggests keeping the upper root zone near pH 6.0 to 6.5.
• Improve drainage, water only when needed, and water deeply rather than lightly and often.
• Reduce thatch and compaction by verticutting and aerating.
• Go light on herbicides; UF/IFAS notes St. Augustinegrass is especially sensitive to them.

Chemical control

Fungicides only work preventively. UF/IFAS says to apply at least a month before symptoms normally appear and then monthly while conditions favor the disease, watering lightly afterward so the product reaches the roots. Texas A&M points to fall, when the fungus is thought to be most active. UF/IFAS lists strobilurin (QoI), DMI and thiophanate-methyl products, warns that some DMIs can injure bermudagrass, and notes some fungicides cannot be used on residential lawns. After symptoms appear, cultural fixes do more than fungicides. Use only products labeled for this use; the label is the law.

Use only products labeled for this disease and this site; the label is the law. For trees, work with an ISA Certified Arborist. If you hire someone to apply pesticides, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Prevention

• Where the disease is known nearby, the UF/IFAS Indian River County office notes preventive treatment can go down before new sod is laid.
• Avoid stress from scalping, overwatering and heavy herbicide use.
• Keep a balanced, slow-release fertilizer program with potassium.
• Fix low, wet areas that stay saturated after rain.

When to call a pro

Take-all root rot is hard to confirm by eye. UF/IFAS asks for live grass that still shows symptoms; dead grass cannot be diagnosed. Contact your county extension office about sending a sample, and talk to a licensed pesticide applicator about preventive timing. See our pesticide applicator license guide.

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