Common fungal diseases of Swiss chard

This week, Bill Kerr looks at Cercospera leaf spot, beet mosaic virus, and the two types of mildew that target Swiss chard.

- Bill Kerr

When it comes to diseases of Swiss chard, one stands out above all others: Cercospora beticola, or Cercospera leaf spot. If you grow Swiss chard or beetroot, you are more than likely to have encountered it.

TRIGGERED BY MOISTURE

The pathogen becomes active under warm, wet conditions and periods of high humidity. Frequent dew, for example, can trigger symptoms. This year has seen severe outbreaks of Cercospera leaf spot in the summer rainfall areas due to the many prolonged wet periods.

The literature on the disease recommends that farmers deep-plough all infected crops, adding that spores can persist for three years on crop residue.

In my experience, however, ploughing doesn’t help; the disease will manifest even where beetroot and Swiss chard have not been planted in the area prior to the current planting.

It can also infect common weeds such as amaranths and