Rhizoctonia on Tomato Plants

Rhizoctonia rot

Rhizoctonia solani is common in most soils and is able to cause some form of disease in almost all cultivated plants. Different ‘strains’ of R. solani, called anastomosis groups, have been recognized. The anastomosis groups differ in their host range and pathogenicity.The most common diseases are damping-off of seedlings, root and stem rots, stem cankers and fruit rot. The diseases often have common names that describe symptoms on the particular host, for example base rot of lettuce, black scurf of potato tubers, crater rot of beetroot, and wire stem of tomato and crucifer seedlings. It is caused by fungus Rhizoctonia solani.

Symptoms

Infection of stems causes dark-colored cankers or rotting at the base of the stem. On plants growing close to the ground (e.g. lettuce), the fungus attacks the older leaves in contact with the soil, causing brown lesions on the leafstalks and leaves. The disease may progress to involve the whole plant, causing wilting and death.

On fleshy, succulent stems, roots and storage organs, the fungus causes brown, rotten areas or sunken cankers that may be covered by fungal mycelium. Infection of potato tubers causes black scurf in which small, dark, flat sclerotia resembling specks of dirt occur on the tuber surface and which are not removed by washing. Fruit growing near the ground can be infected, developing firm, water-soaked areas that become sunken and often crack open.

Control

Cultural and non-chemical control

Prevent fruit from contacting the soil by staking plants and using plastic mulches. Varieties highly susceptible to Rhizoctonia fruit rot should be avoided, especially if plastic mulch is not used.

  • Grow seedlings in soil-less potting mixes or in sterilized or pasteurized soil.
  • Treat seed with the recommended fungicide before planting.
  • Maintain optimum plant growth and avoid injuring plants, as wounds provide a means of entry for the fungus.
  • Where possible, avoid soil contact of fruit by using plastic mulch or by staking plants.
  • Ensure crop residues decompose thoroughly before replanting an area.
  • Applications of fungicides to the soil provide control of some diseases caused by R. solani.

Chemical control

Fumigation of plant beds will eradicate seedling pathogens, such asrhizoctonia solani; however, fumigated soil can become reinfected if pathogen-infested field soil is moved to fumigated areas.

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