Take-All Root Rot

Take-all root rot (TARR) is a fungal disease affecting most warm-season grass species, such as Bermuda, Zoysia, and St. Augustine grasses. The disease is called “take-all” root rot because if left unchecked, it “takes all” the grass by killing the root, leaving patches of bare soil. It is caused by the fungus Gaeumannomyces graminis var. graminis.

Take-all root rot prevents the grass roots from taking up water and nutrients from the soil. The first sign of TARR is grass that looks yellow and sickly. As it progresses, it causes severe dysfunction of the roots. The affected turfgrass will start dying in patches. Diagnosis by an expert is usually possible without laboratory testing.

The fungus is most prevalent when soil temperatures are within its ideal range (55–85 °F.). Our soil temperatures typically fall within this range for two periods each year:

1. March–April: when grass begins to emerge from winter dormancy.
2. September–November: when temperatures have fallen from their summer highs.

TARR also favors alkaline (high pH) soils which are prevalent in Dallas.¹ We see infestations most frequently on established lawns. Sodded lawns carry soil from the nursery, which is normally treated with fungicide to prevent TARR.

Preventing Take-All Root Rot

Preventing TARR can be challenging. The pathogen is very widespread. In a 1999 survey of Dallas lawns, Dr. Phil Colbaugh found the TARR pathogen in 61% of lawns surveyed.² Furthermore, most turf grasses used in our area are susceptible to the disease. As such, prevention efforts focus on improving overall turf health.

To improve overall turf health, two important factors to address are watering and mowing.

Watering

Watering appropriately and ensuring proper drainage is an important part of keeping your turf healthy.

Our local soils are clay-heavy and drain very slowly. Construction, vehicles, and other human activities worsen water flow by compacting the soil. Combined with natural topography, your landscape likely has some areas with poor drainage.

Mowing

Another important element of turf health is mowing height. Mowing too short can make TARR more severe. You should also mow frequently enough to avoid removing more than one-third of the leaf height at once.

Additionally, turf in shaded areas of your landscape should be left taller than turf in sunny areas. The leaf blade is like a solar panel; shaded turf needs more surface area.

Unsure how high you should be mowing? This guide from the Texas A&M AgriLife Extension is a great primer.

Treating Take-All Root Rot

Treating take-all root rot takes a multi-faceted approach. First, we stop any cultural practices that could inhibit treatment.³ After diagnosis, we usually begin treatment with fungicide applications. The applications give us a foothold to improve environmental conditions and make the soil unsuitable for the TARR pathogen.

The TARR pathogen does best in alkaline soils, so using soil amendments to lower the pH is another treatment option. We do this by adding peat moss or an acidifying fertilizer to the soil. However, any pH treatment will eventually be counteracted over time by our alkaline water supply.

Once a site has been infested, preventative fungicide injections should be made in following years during the windows when TARR is active.