Question: The St Augustine grass in our yard shows significant dying-out. I don’t see any grub worms; I’ve applied fungicide and fertilizer with no success.
A neighbor told me about the St. Augustine root rot problem called Take All Root Rot. What is that? Ken, Brownsville, Texas
Answer: Ken, Take-All root rot may sound like a made-up name, but it is for real. It turns out to be a very destructive root fungus disease on St. Augustine grasses (all varieties). Take-all has been found from Florida to Texas and California as well.
There have been several “findings” that contribute to the spread of this soil-inhabiting lawn fungus disease – Gaeumannomyces graminis var. graminis.
- Heavy spring & summer rains
- Heavy lawn lime soil
- Lawn Fertilizers containing heavy nitrates
- Micronutrient deficiencies
St Augustine is not the only grass the Take-All root rot fungus hits. The fungus has also been found on bermuda grass, zoysia grass, and centipede grass.
First Symptoms
I know you’re wondering, “Why is my St. Augustine grass dying?”.
Usually, the first symptoms of root rot in St. Augustine grass show up in spring and early summer.
The lawn has a yellow-green cast from the yellow leaves called chlorosis. As the fungus progresses, a severe thinning in irregular patches occurs as infected stolons begin to die.
If all grass dies in an area, it is soon replaced with weeds.
Shady areas do not seem to show as much damage as grass in areas with lots of sun. St Augustine grass with a “heavy dose” of take-all root rot looks patchy and in decline when accompanied by a weak root system.
In areas where St Augustine grass does not go completely dormant, the greatest recovery from the fungus happens during the winter. However, when spring rains return, so do the symptoms often.
Take All and Brown Patch Confusion
Often, the fungus called “Brown Patch” and “Take All root rot“ are confusing, as they carry very similar symptoms.
Brown Patch
- Rotted leaf blades and sheaths
- Unharmed roots and stolons
Take-All Root Rot
- Undamaged leaves and leaf sheath
- Usually badly rotted roots, rhizomes, and stolons, dark brown or black in color
St. Augustine sod damaged by the fungus often looks as if it has the same usually yellowing foliage professionals associate with an iron deficiency.
Soil Types Not A Factor
Currently, the type of soil in which the St. Augustine grass is “planted” does not appear to be a factor.
Fungal diseases have been found in clays and fine sandy soils.
How to Treat Take-All Root Rot St. Augustine
The Take-All root rot does not seem to play favorites regarding the varieties of St. Augustine grass that can “resist” being affected.
The following St Augustine cultivars in sod farms and homeowners lawns have all been “victims” of the root rot.
- Common
- Raleigh
- Floratam
- FX-10
- Jade
- DelMar
- Dalsa 8401
- Mercedes
- Bitterblue
- Standard
- California Common
- Sunclipse
- Seville
So far, the “best” solution for st augustine root rot control is not chemical but proper turfgrass management practices.
Nitrogen – nitrate nitrogen (ammonium nitrate and calcium nitrate) appears to play a part the the occurrence of the fungus. Avoid using fertilizers containing the above nitrogen forms. If used, maintain equal amounts of potassium.
The “preferred” forms of ammonium-containing fertilizers (such as ammonium sulfate, urea, and ammonium chloride) are recommended nitrogen sources for well-managed St. Augustine grass lawns.
Instead of heavy fertilizer applications (which may contribute to disease development), monthly light applications of nitrogen are recommended.
The other option is applying slow-release fertilizers to maintain growth over the growing season.
Mirco-nutrient deficiencies may also contribute to the fungi’s “living environment.” Foliar applications of micro-nutrient supplements can also be beneficial.
If serious micro-nutrient deficiencies are present, soil applications of manganese sulfate may be needed to correct the deficiencies.
A soil test is always advisable to learn the makeup of your soil and its pH.
Lime used to help manage soil pH has been linked to increases in the fungus. Usually, it is heavy lifting to watch out for.
For St. Augustine grass, try to maintain a soil pH of 5.5 to 6.0 on heavily managed lawns. Apply no more than 10-20 pounds of lime per 1,000 square feet yearly.
Other turf management practices to consider:
- Raising cutting height for drought-stressed lawns
- Timing irrigation
- Improving drainage in wet areas
Lawn Renovation
Recovery is very often poor in St. Augustine grass root rot. The only choice may be a complete lawn renovation. However, laying new St. Augustine turf over “infected” areas is just not advisable.
Laying down Bermuda or Zoysia grass is not a good option since both of these grasses are hosts to this nasty grass fungus as well.
The best option for grass replacement may be Centipede grass since few St Augustine fungus cases have been reported.
Take All Root Rot Treatment: Chemical Controls
Controlling the Take-All root rot fungus with chemical applications has not achieved the best results.
Due to the high cost of the best fungicide for take-all root rot, treatment applications are usually limited to spot treatment.
The Take All Root Rot St Augustine grass fungus so far has proven to be a battle not won with chemicals but with using best turf management practices.