Take-all patch, caused by the fungus Gaeumannomyces graminis var.
graminis, is a serious disease of St. Augustinegrass and can also
cause problems in bermudagrass. The causal organism seems to be most active
during the fall, winter and spring when there is abundant moisture and temperatures
are moderate. The disease has the ability to destroy large sections of turfgrass
if left uncontrolled, and has proven to be a difficult disease to control.
Symptoms. When the disease is active, the first symptom is often
a yellowing of the leaves and a darkening of roots. The area of discolored
and dying leaves may be circular to irregular in shape and up to 20 feet
in diameter. A thinning of the turfgrass within the affected area occurs
as roots, nodes and stolons become infected and the plants decline. Unlike
brownpatch, the leaves of take-all infected plants do not easily separate
from the plant when pulled and the stolons will often have discolored areas
with brown to black roots. The roots are sometimes so rotted that damaged
stolons are easily pulled from the ground. Roots and stolons of brownpatch
infected plants usually have a healthy appearance. Regrowth of the grass
into the affected area is often slow and unsuccessful as the new growth
becomes infected. During the stressful high temperatures of the summer months,
the weakened, infected turfgrass will continue to decline.
Disease Cycle. The pathogen survives on infested debris and on infected
perennial parts of living grass plants. When conditions are favorable (cool,
moist weather), the fungus grows on the surface of roots, stolons, rhizomes,
crown and leaf sheaths of the grass and then penetrates and infects the
tissues. As the weather becomes warmer and dryer, the infected plants are
stressed, and symptoms become more evident. The pathogen can be spread over
long distances when infected plants or plant debris are transported mechanically.
Infected sod may serve as a source of inoculum even if it shows no immediate
symptoms of the disease.
Control. Controlling take-all patch is not easy and much has yet
to be learned about this disease. Control efforts should consist of both
cultural and chemical methods. Good surface and subsurface drainage is important.
Excessive watering can also favor development of take-all patch. Irrigating
only when required to maintain good plant growth and vigor is suggested,
and infrequent but thorough watering is preferred to frequent shallow watering.
Since the pathogen can survive on infested thatch, prevention of thatch
build-up is suggested. Efforts to dethatch and to prevent thatch accumulation
may prove helpful. If soil compaction exists, aerification will help to
alleviate this condition and allow the grass to establish a deeper, more
vigorous root system.
The fungicide Rubigan is effective for the control of take-all patch caused
by Gaeumannomyces graminis. Since infection is thought to occur primarily
in the fall, with disease progression continuing during the fall and winter
months under cool moist conditions, fall applications may be the best time
for fungicides to be applied for preventative purposes. Its efficacy in
controlling the already established disease may be disappointing.
Where soil acidification is practical, the use of acidifying nitrogen fertilizers
and elemental sulfur is recommended. The causal agent for take-all patch,
G. graminis, does not thrive under acid soil conditions.