Rhizoctonia solani
Rhizoctonia oryzae
Ceratobasidium sp.
- Symptoms: Bare patch will cause patches of stunted plants within an otherwise apparently healthy crop, with the patches often being circular or elongated in the direction of sowing. Patches are more likely to appear in clusters rather than being randomly distributed, and are most obvious 2-3 weeks after emergence through to tillering (picture at left). There are a wide range of symptoms for bare patch, which can be very similar to those of moisture and nutrient stress. These symptoms include dark green coloring and a purple tint to the most recently formed leaves, yellowing of lower, older leaves, spindly grown, failure to produce tillers, little to no growth (stunting), poor yield, and shriveled grain. Below the ground, bare patch will cause the rotted cortex tissue to slough off, leaving the stele exposed, which eventually rots through, leaving a pointed stub referred to as a ‘spear tip,’ which are usually yellowish brown in color (picture at right).
- Development: The fungus survives hot, dry periods in the absence of a host in dead plant material. Infection is favored by sandy, calcareous soils, though bare patch in the Pacific Northwest of the USA is associated with well-structured, brown, silt-loam, loess soils with high available calcium. The greatest damage caused by this disease occurs at 12-15 degrees Celsius, but the disease occurs into at least the upper 20’s.
- Hosts/Distribution: The host ranges of bare patch fungi include, but are not limited to, wheat, barley, corn, grasses, alfalfa, peas, triticale, rye, oats, beans, rapeseed, canola, clover, sugarbeet, dicotyledonous weeds, cotton, and tobacco. Bare patch has had documented distribution in Australia, England, Canada, Scotland, the USA, South Africa, and Tanzania.
- Importance: Economic losses due to bare patch are not well characterized, but studies in two Australian states estimated that overall losses in single fields were 75% in Western Australia, and 77% in South Australia, indicating a severe problem for individual farmers. Economic losses due to bare patch in the Australia are similar to those in the Pacific North-West of the United States.
References:
- Professor Stephen M. Neate- Senior Plant Pathologist, Lesley Research Centre, Toowoomba, Queensland, Australia.
- Dr. Hugh Wallwork- Senior Plant Pathologist, South Australian Research Development Institute, Australia.