Rhizoctonia is a fungal pathogen that is no more prevalent in one area than any other, but it’s a long-term and constant threat. Here are some up-to-date management reminders.
Use long rotations
A University of Saskatchewan trial that finished in 2007 showed that long rotations and application of fungicides in-furrow appeared to reduce problems with rhizoctonia, particularly black scurf.
It stays in the soil
The study also concluded that soil inoculum rather than contaminated seed “is the major factor in determining the severity of the disease.” The disease is hardy and can survive on weeds of the nightshade family or on volunteer potato plants. Aim for quick crop emergence. This helps prevent disease development. If the disease has been allowed to get a foothold once potato plants have emerged, it is too late to repair plant stand damage.
Use clean seed
Prevention is the best management strategy. Use clean seed, fungicide treatments and as long a rotation as possible. Seed tubers should have no more than two percent sclerotia on their surfaces. Wash them in order to accurately assess severity of contamination.
Use an in-furrow fungicide
Dr. Ron Howard with Alberta Agriculture and Rural Development, says that while seed treatments kill fungi on or immediately around the seed piece, in-furrow products kill rhizoctonia in the soil and provide a protective zone for young roots.
DuPont™ Vertisan™, a next-generation Group 7 fungicide has recently been registered for use. It delivers preventative and residual activity on a number of diseases in potatoes, including rhizoctonia.