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Diseases of periwinkle ( Catharanthus sp. ) in Arizona

Rhizoctonia root rot

Rhizoctonia root rot is caused by Rhizoctonia solani, a common soil borne fungal pathogen that causes root rot of periwinkle (sometimes called vinca) and many other bedding plants. The fungus most commonly attacks seedlings causing “damping off” ( and transplants, but it may cause root rot of larger plants also. Symptoms are wilting and/or yellowing and stunting. On hot summer days, infected plants may wilt rapidly and do not recover with increased watering (photo 1). Small plants die quickly.

Rhizoctonia solani does not produce spores, but it is able to persist in soil or organic matter as hyphae or as sclerotia. Periwinkle should not be replanted in areas where disease occurs. Rotate to a plant such as marigold that is more tolerant. Few fungicides are effective against Rhizoctonia, but a few such as Banrot and Abound can be used to prevent disease by applying as a soil and root drench before disease symptoms appear. When selecting plants, be sure the plants are not root bound in the container. When planting, be sure not to place the plants too deep; the top of the root ball should be at the soil surface or slightly above.

   1 Rhizoctonia root rot showing rapid wilting of periwinkle plants

August 8, 2013