From Clemson Plant Pathologist Tony Keinath.
Once beets emerge from the ground, the biggest challenge South Carolina growers face is keeping the leaves free of Cercospora leaf spot. This disease is a problem wherever beets are grown for greens or bunching (roots sold with tops attached). Cercospora leaf spot does not affect the weight or size of roots, so growers who sell only roots do not need to spray or do not need to be concerned if spraying fungicides does not eliminate Cercospora.
Some beet cultivars have “intermediate resistance” (IR) to Cercospora leaf spot. Does this low level of resistance hold up under heavy disease pressure? Based on the results of my 2021 experiment, the answers are “yes” and “no.”
Two cultivars with IR, Touchstone Gold and Vulture, had less disease than the most susceptible cultivar, Chiogga Guardsmark. Touchstone Gold had less disease than Vulture. However, neither cultivar seemed very heat tolerant, as both produced fewer leaves than the other four cultivars. And both IR cultivars still had too much disease and too few healthy, marketable leaves to recommend.
In general, the more disease a cultivar had, the lower the percentage of healthy marketable leaves it produced (Figure 1). Bull’s Blood and Ruby Queen produced a greater percentage of healthy leaves and a greater marketable weight of healthy leaves (weights not shown) than the susceptible cultivars Cylindra and Chiogga. Based on this experiment, Ruby Queen would be the best standard green-leaf, red-rooted cultivar of the six for bunch beets or beet greens. This trial is being repeated in 2022.