Stem canker

Rhizoctonia solani

Symptoms on the young shoots

• Light to dark brown, sunken lesions on underground part of the stem
• Lesions have many dark brown fungal threads visible under a magnifying glass
• The growing point of the young shoot dies back resulting in a proliferation of side shoots
• Process repeats until the energy of the seed tubers is expended
• Serious infection results in irregular emergence and missing plants

Foliar symptoms

• Stems can also be infected with top leaves appearing pinched
• Sometimes white fungus surrounds the stem base forming a ‘cuff’
• Tubers or bottle-shaped growths develop in the leaf axils
• In severe infections, small aerial tubers can form above ground
• Stolons can die resulting in green above-ground tubers close to the stem

Infection and spread

• Via seed tubers
• Slower emergence and growth (eg low soil temperatures) increases the chance of infection
• Naturally present in the soil

Possible confusion with

• Infestation by nematodes