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Spring and Winter Canola:
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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: Spring and Winter Canola >Seedling Disease Complex |
Stand establishment is a major concern in canola production. Poor stand establishment is often due to seedling disease infection by one or more fungi; this is referred to as a "seedling disease complex." The primary fungi involved are Rhizoctonia, Fusarium and Pythium. The problem is greatest under cool conditions.
Infection by these fungi or complex can exhibit many different symptoms. These include seed decay or rot, pre- and postemergence damping-off, seedling blight and seedling root rot. These symptoms occur during the first 4 weeks or by the fourth-leaf stage. Seeds may fail to germinate or die shortly after emergence. Seedlings that emerge may appear normal but can have significant root rot. Damping-off occurs when root decay or rot moves up the stem (hypocotyl) causing a girdling or pinching of the stem at or near the soil surface. The stem is weakened and is susceptible to breakage or toppling, where the characteristic reddish-brown lesions are formed. Infected seedlings often wilt or die when stressed because of a reduced (root pruning), constricted or rotted root system, especially under dry conditions. Stands are slow to emerge, thin or patchy. Yields can be reduced when stands are uneven or patchy. Severe plant loss may result in reseeding.
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These fungi survive in the soil on decaying plant residues. Conditions that cause the developing seed or seedling to grow slowly are ideal for these fungi. The below-ground parts of the seedling harden (woody) at the two- to four-leaf stage and vigorously growing plants reach this stage quicker. At this stage, the seedlings are able to limit further infection and can regenerate roots quicker than they are lost. Pythium prefers cool, wet soils, whereas Rhizoctonia favours dry, light soils.
Plant good quality seed into a firm, moist seedbed when the conditions are suited to promote rapid germination. Fungicide seed treatments will reduce infection and increase stand establishment. (Refer to OMAFRA Publication 812, Field Crop Protection Guide.) Maintain good fertility balance and avoid excess fertilizer, which promotes disease and phytotoxicities. Avoid deep planting of seed. (Order OMAFRA Publication 812)
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