Ring spot is a fungal disease that affects many crops and leads to poor productivity. In this article from the “WORLD OF PLANTS” website, we discuss the symptoms of infection, the causes of the disease, and methods of effective prevention and control.
Cause of ring spot disease
- Ring spot
- Mycosphaerella brassicicola: scientific name
- Type of disease: fungal
The damage is caused by the airborne pathogen Mycosphaerella Brassicola. The spores are spread by water splashes, wind and rain. The fungus needs a period of 100% relative humidity lasting at least four days to reproduce. Temperatures of 16 to 20°C and poor soil drainage can support growth of the pathogen. Disease is mostly a problem in seed production, and seeds may carry the pathogen. The fungus overwinters on infected weeds and other host crops or in detritus. The spores are spread by wind. Cold, wet weather makes the disease worse.
Spread of ring spot disease
The damage is caused by the airborne pathogen Mycosphaerella Brassicola. The spores are spread by water splashes, wind and rain. The fungus needs a period of 100% relative humidity lasting at least four days to reproduce. Temperatures of 16 to 20°C and poor soil drainage can support growth of the pathogen. Disease is mostly a problem in seed production, and seeds may carry the pathogen. The fungus overwinters on infected weeds and other host crops or in detritus. The spores are spread by wind. Cold, wet weather makes the disease worse.
Hosts of ring spot
Members of the cabbage (Brassica) family, e.g., broccoli, Brussels sprouts, cabbage, cauliflower. Weeds in the Brassica family can be hostas.
Conditions suitable for ring spot disease
The weather is cold and wet
Life cycle of ring spot disease
A major disease of brassicas, caused by a fungus; It is common in areas of intensive production, with crop overlap. It can be particularly severe when wet weather occurs for 1-2 weeks, at temperatures between 16-20°C. Ringspot disease is most important in Brussels sprouts, cabbage, and cauliflower.
The fungus causes light brown to gray spots surrounded by a yellow halo (Image 1). The spots are often limited by veins, angular, and up to 20 mm wide. Characteristically, small black fruiting bodies containing large numbers of spores develop in concentric circles in the center of the spots (Photo 2). These give the disease the name “ring spot”.
Spots appear on seedlings, but often appear on mature plants, on old leaves. If there are many spots clustered together, the leaves turn yellow and die early. Spots also occur on Brussels sprout sprouts.
The spread of the fungus occurs when the fruiting bodies release spores that are spread over a short distance by water spray and in wind and rain. Long-distance dispersal can occur in seeds.
Effect of ring spot disease
Economic damage is caused by premature death of leaves, by bud infections on Brussels sprouts, and by spots on cabbage that penetrate several layers of stored leaves and must be removed before sale.
Symptoms of ring spot disease
The disease appears in the form of dark spots surrounded by yellow circles.
Dark concentric rings within the spots.
And yellowing of leaves.
. Premature leaf fall.
Symptoms are usually most common on older leaves, but if younger leaves are affected, symptoms become more severe. Small dark spots of 3-5 mm, surrounded by a yellow halo, initially appear on the leaf surfaces. The color of these spots is green-brown or gray-black and limited to the veins of the leaves, and their size eventually becomes 2-3 cm. Small dark dots form concentric rings within the spots. The spots may accumulate, causing yellowing of the leaf. In severe infestation, it may result in premature leaf drop. The spots caused by the ring spot fungus look similar to those caused by the alternative species. The main difference is that the spots of ring spot are gray in color and contain pinhead-like dots of black in concentric rings. Symptoms may appear on all aboveground parts of the plant. The individual spots have concentric dark rings, and the spots on the fruiting bodies are black, with specific edges surrounded by a yellow area. In severe attacks, spots accumulate, and the entire plant may be affected and turn black. The fungus in the seed stalks causes disfigurement similar to injury caused by the herbicide 24-D. Dark spots may appear on stored cabbage and may penetrate deeply.
Preventive measures for ring spot disease
- Use resistant varieties if available.
- Monitor your nursery for leaf spots, remove affected leaves, or if more spots are present, destroy the seedlings.
- Plant only healthy seedlings in your field.
- Remove and destroy weeds from and around your field, as they can be alternative hosts.
- Collecting crop residues and destroying them by burning or burying.
- Alternatively, you can plow the infected stubble.
- Wait until the residue has completely rotted before replanting in the field.
- Consider a 2-3 year crop rotation with a non-host crop.
- Treat the seeds with hot water at 122°F for 30 minutes.
- This eliminates seed-borne fungi.
- Treat a small amount of each batch of seeds, and test for germination before treating each seed.
Ring spot disease recommendations
We recommend applying organic control in the early stages of the disease or when the crop is close to harvest. In the more advanced stages of the disease, please use chemical control. It is not recommended to mix or use different products at the same time.
Organic control of ring spot disease
To date, we are not aware of any biological control method available against this disease. If you know of any successful way to reduce the incidence or severity of symptoms, please contact us.
Chemical control of ring spot disease
Always consider an integrated approach with preventive measures together with biological treatments if available. You can treat the seeds before planting with thiram or mancozeb. During cold and humid weather you can spray chlorothanonil, mancozeb or copper. It is worth noting that it is a difficult disease to control as intensive vegetable production occurs due to large numbers of airborne spores where environmental conditions are cold and humid, which favors the spread and infection.
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References
Author Graham Jackson
Information from the Pests and Diseases Fact Sheet – Mycosphaerella Brassicola. Gardening week. ( http://www.hortweek.com/pest-disease-factsheet-mycosphaerella-brassicola/plant-health/article/1341919 ); From (including images 1 and 2) Diseases of vegetable crops in Australia (2010). The editors, Dennis Persley, et al. CSIRO publication.
Produced with support from the Australian Center for International Agricultural Research under project PC/2010/090: Promoting integrated crop management research in the Pacific Islands to support the sustainable intensification of high-value crop production, implemented by the University of Queensland and the Pacific Community Secretariat.
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