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Soybeans:
Phomopsis Seed Mould,
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| Author: | OMAFRA Staff |
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| Creation Date: | 01 March 2002 |
| Last Reviewed: | 01 March 2002 |
| Agronomy Guide > Pub 811: Soybeans > Phomopsis Seed Mould, Pod and Stem Blight |
Excerpt from Agronomy Guide for Field Crops (Chapter 4)
Traditionally, Phomopsis seed mould has been Ontario's most important soybean seed disease. It is most problematic when the weather conditions at harvest are warm and wet. Delaying harvest under these conditions will increase the incidence of this disease.
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There are two Phomopsis diseases that occur in Ontario: Phomopsis seed mould and Phomopsis pod and stem blight. Phomopsis seed mould is characterized by fine cracks that usually develop near the hilum of the infected seed. A white or grey mould may be visible on the seed surface. The yield, grade, viability and vigour of the seed can be reduced. Yield losses occur because severely infected seeds remain small and light and may be lost during harvest and cleaning operations. The second phase of the disease is referred to as "pod and stem blight." Although plants are infected early in the season, symptoms do not become apparent until after mid-season. Symptoms on the stems appear as small, black, raised dots or bumps (pycnidia). These bumps are arranged in rows or islands on the stem. On the pods, there are also numerous black dots but they are not arranged in any particular pattern.
Plate 66. Phomopsis seed mould causes fine cracks and mould, starting near the hilum, reducing quality and seed vigour.
Plate 67. Phomopsis pod and stem blight symptoms include small, black, raised dots or bumps arranged in rows or islands on the stem.
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The fungus overwinters in seed and crop debris. Spores of the fungus are splashed on to developing plants early in the season. Warm, wet, humid weather during pod fill favours disease development.
Whenever possible, grow full-season varieties that mature during the cool weather late in the growing season. Varieties that are short-season for an area tend to mature earlier when conditions are warmer and more favourable for seed mould. Pod and stem blight can be controlled or reduced by integrating one or more of the following: disease-free seed, planting later, crop rotation, plowing under soybean debris and well-timed harvest. Harvest soybeans destined for export or seed first. Seed treatment usually increases germination and emergence of seed. However, distorted seed with visible fungal growth often fails to germinate, even when treated. For information on registered seed treatments, refer to OMAFRA Publication 812, Field Crop Protection Guide. (Order OMAFRA Publication 812)
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