Question: The St Augustine grass in our yard shows significant dying-out. I’ve don’t see any grub worms, I’ve applied fungicide and fertilizer with no success. A neighbor told me about Take All Root Rot on St. Augustine. 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” which 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.
I know you’re wondering, “why is my St Augustine grass dying?”.
Usually the first symptoms of take-all root rot show up in spring and 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 the damage as much as grass in areas with lots of sun. St Augustine grass with a “heavy dose” of take-all root rot, looks patchy in decline when accompanied with 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, often so do the symptoms.
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.
- Rotted leaves and leaf sheaths
- Unharmed roots and stolons
Take-All Root Rot
- Undamaged leaves and leaf sheaths
- Usually badly rotted roots and stolons, dark brown or black in color
St. Augustine sod damaged by the fungus often look as if the have the same usually yellowing foliage professionals associate with an iron deficiency.
Soil Types Not A Factor
Currently, the type of soil the St. Augustine grass is “planted” in does not appear to be a factor. The fungus disease has been found in clays to fine sandy soils.
Control on St Augustine Grass
The Take-All root rot does not seem to play favorites when it comes to the varieties of St. Augustine grass which can “resist” being affected. The following St Augustine cultivars in sod farms and homeowners lawns have all been “victims” of the root rot.
- Dalsa 8401
- California Common
So far the “best” solution for 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.
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 lawn.
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 season.
Mirco-nutrient deficiencies may also contribute to the fungus “living environment.” Foliar applications of mirco-nutrient supplements can also be beneficial. If serious mirco-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 make up of your soil and its pH.
Lime which is used to help manage soil pH has been linked to increases in the fungus. Usually it is heavy liming 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
Recovery is very often poor in St. Augustine grass. The only choice may be a complete lawn renovation. However, laying new St. Augustine turf over “infected” areas with is just not advisable.
Laying down Bermuda or Zoysia grass are not good options 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.
Controlling the Take-All root rot fungus with chemical applications have not achieved the best results.
Due to the high cost of fungicides, 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.