Take-All Root Rot (TARR) is a fungal pathogen that is very common in our area and was particularly active this past year. While I always get a lot of questions regarding lawns, I noticed a definite increase this past season. In speaking with colleagues around the state, it seems this has been the case all around Texas — especially those counties closest to the coast.
If you’ve noticed your lawn slowly yellowing, then thinning out and leaving behind irregular shaped dead patches, you are most likely dealing with TARR. Even though the symptoms indicate that it is probably TARR, I always recommend submitting a sample to the Texas Plant Disease Diagnostic Lab (https://plantclinic.tamu.edu/). Analysis often reveals multiple issues, including lesser known fungal pathogens and pests. It’s very important to know what you are dealing with in order to treat it effectively.
The main thing to understand about TARR is that it is prevalent in our soils because it prefers high pH, which is what we have here. So it’s very unlikely your lawn service brought this pathogen from your neighbor’s yard. A more accurate assumption would be that it was always there and a cultural practice or weather event has caused it to become active.
Prevention is the most effective approach; this disease can become a serious problem when the turfgrass is under stress because of unfavorable environmental conditions and improper management. Excessive shade, herbicide injury, soil compaction, temperature extremes, imbalanced soil fertility, inappropriate irrigation scheduling, improper mowing height or frequency, or any other condition that weakens the turf can cause TARR to become active.
Here are some steps you can take to ensure your lawn is healthy and stress free:
>> Soil testing – there is some correlation between TARR and high rates of nitrogen. If you fertilize every year, it may be a good idea to have a soil test done; it’s very possible you are adding unnecessary fertilizer.
>> Soil hole test — poor drainage is a common trigger for TARR. Test your soil’s drainage by digging a hole 6 to 8 inches in diameter and 2 feet deep.
Fill it with water and time how long it takes to drain; 15-30 minutes is ideal. Any longer than that would indicate poor soil drainage.
>> Irrigation — watering can be tricky; you don’t want too much, but you need enough. When it’s hot, consider breaking up your irrigation into 10 minute cycles to allow the water time to percolate into the soil. In cooler weather, use a screw driver to poke a hole about 3 inches down into the soil, if you feel moisture, don’t water.
>> Mowing height — cutting your lawn too short is one of the quickest ways to stress it out. Know the appropriate mowing height for your lawn and leave it a little longer in shady areas.
If you have confirmed that your lawn does have TARR, there are some options for control.
Through a few trials and result demonstrations done in other areas of the state this seems to be the most effective control: a fall application of a preventative fungicide and a top dressing of peat moss applied at the rate of 1 bale (3.8 cu ft)/1000 sq.ft. and an additional top dressing of peat moss in the spring.
Peat moss is acidic so it helps to neutralize high soil pH making TARR less active.
Additionally, some colleagues recalled a Bermuda grass study where they paired peat moss with Lesco Iron and had very positive results.
I’m interested in how the Iron could potentially help in our area as our soil chemistry ties up iron in the soil making it unavailable to plants, causing iron deficiencies.
If you plan to add an iron product look for a foliar one. It needs to be applied as a spray, otherwise it will just get tied up in the soil and the grass won’t be able to utilize it.
Ashley Gregory is the Horticulturalist for Hidalgo County with Texas A& M AgriLife Extension Service. She can be reached at the Hidalgo County Extension Office at (956) 383-1026 or by email at [email protected]u.edu.