Blackleg is caused by the fungus Phoma lingam (Leptosphaeria maculans). Sexual spores (ascospores) are produced during cool, wet weather and are disseminated by wind, splashing water, and contaminated seed. Young, succulent canola tissue is most susceptible to infection, especially during the first few weeks of growth. The pathogen survives in infested crop debris and contaminated seed.
Black leg can cause lesions on leaves and stems, above or below the soil. Infected stems have a characteristic semi-dry, blackened rot with small black fungal fruiting bodies (pycnidia) covering the infected area. Affected plants are often stunted and wilt. Blackened streaks are apparent when stems are cut in cross-section.
A stem canker can occur when the fungus grows systemically through the petioles into the stem. Patches of plants in the field will lodge and break off at the soil line. A white to ash-gray, brown, or black-lesion develops near the soil line.
No biological control strategies have been developed for black leg.
Plant seed free from the black leg pathogen. Practice a three-year or longer rotation to non-hosts such as small grains. Resistant varieties are available and should be planted. Deeply incorporate crop residues after harvest to reduce pathogen survival. Eliminate cruciferous weeds and volunteers.
Fungicides are most effective when used in combination with cultural control strategies.
Product List for Blackleg:
Pesticide |
Rate per Acre |
Application Frequency |
Remarks |
Azoxystrobin |
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Quadris |
6.2-15.4 oz |
7-14 days |
Maximum of three applications (27 oz); Beginning applications at 10-25% bloom; Do not make application past 95% petal fall; |
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The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality. |
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Categories: Canola and Mustard, Disease, Blackleg
Date: 12/30/2004