This archive report was first published on 23 May 2020.
Published on May 23, 2020, by ANN MACHARIA, a renowned agricultural expert.
Ring spot disease is a common and severe fungal infection that affects cabbages and other members of the brassica family, such as sukuma wiki (collard greens) and cauliflower.
The disease is characterized by yellow patches and circular brown-grey spots on the leaves, surrounded by a green margin or black-specked concentric zones.
According to agricultural experts, the fungus causes light-brown to grey spots on the leaves, surrounded by a yellow halo, and tiny black fruiting bodies containing large numbers of spores develop in concentric circles in the centre of the spots.
Ring spot disease affects young seedlings and is more severe in mature and old plants, causing the leaves to turn yellow and die early.
It is easily spread by wind, water splashes, and compost made from infected crop remains, and can be spread in distant places through the movement of seeds or seedlings.
Managing ring spot disease requires establishing nurseries far from affected fields, using certified seeds resistant to the disease, and scouting for affected seedlings to remove and destroy them.
Other management strategies include avoiding overlapping crops of the brassica family, removing weeds that act as alternate hosts, and sanitizing tools regularly to prevent the spread of the disease.
Additionally, planting border crops that act as windbreakers and considering the source of manure can help prevent the spread of the disease.
Chemicals available in agrovets can also be used to control the disease.
Cabbages do well in well-drained sandy or silty loam soils with high organic matter content and a pH of 6.0 – 6.5, and ensuring the soil is well-drained can help prevent waterlogged conditions that can lead to yields reduction.
