Soybean
Target Spot of Soybean
Corynespora cassiicola
Fungus
In a Nutshell
- Irregular reddish-brown lesions on leaf.
- Lesions with light green to yellow margins.
- Larger lesions have light or dark rings.
Can also be found in
Soybean
Symptoms
Target spot is mostly a foliar disease. Leaves show round to irregular reddish-brown spots surrounded by a yellowish green halo. The growth of these spots often results in a zonate pattern of light- or dark brown rings, hence the common name target spot. Stems and stalks can also be affected and usually develop dark brown specks or elongated lesions. Small, circular black spots later appear on pods. Severe infections may cause leaves to drop prematurely.
Recommendations
Organic Control
No alternative treatment is available against target spot disease.
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatment if available. The use of fungicides is rarely economically viable. Products containing mixtures of pyraclostrobin, epoxiconazole and fluxapyroxad or bixafen, prothioconazole and trifloxystrobin might help to control the fungus.
What caused it?
The fungus Corynespora cassiicola overwinters on crop debris and in the soil. Favorable conditions for the infection are high humidity (>80%) and free moisture on leaves. Dry weather will suppress the development of the disease. The disease is potentially serious on late-maturing varieties or on susceptible varieties in seasons of high rainfall.
Preventive Measures
- Use high-yielding varieties to avoid economic damage.
- Plant earlier and with early maturing varieties to avoid peak infestation.
- Clear the field thoroughly from plant residues after harvest.
- Rotate with nonhost crops and avoid monoculture in same area.
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