Cause A fungus, Fusarium oxysporum f. sp. lini, which survives in soil and plant debris as thick-walled, dormant chlamydospores. These spores germinate in response to exudates from nearby plant roots. Hyphae then penetrate the roots, colonize the cortex and move into the xylem tissue. Small spores (microconidia) are produced and carried up into the plant. The fungus sporulates on decaying plant tissue, and these spores can be moved by wind or rain to spread disease. This fungus can also be seedborne. Disease is favored by warm weather and often occurs in patches.
Symptoms Plants may be attacked at any stage of development. Seedling blight can occur when soil temperatures are high while flax is in the seedling stage. When older plants are attacked, leaves turn yellow or grayish yellow, and growth stops. Often the top of an affected plant turns downward. Sometimes plants die completely, or the primary stem dies and new, apparently healthy laterals arise from the stem base.
Cultural control
- Rotation between flax crops should be at least several years.
- Use Fusarium-free seed at sowing.
- Use resistant cultivars. The cultivar Cascade is resistant to wilt.
- Use a soilless medium or pasteurized soil to start seedlings. Also disinfect any tools and equipment that might be used and contaminate the media.
- Use care in watering. If using a hose, take care not to splash, and keep the nozzle and hose off the ground, walkways, or other surfaces that may be contaminated.
- Keep benches and premises clean. Do not use sides of low benches as a footrest; soil on shoes may be contaminated. Keep walkways and areas beneath benches clean and free of plant debris.
- Use composted hardwood or conifer bark. The suppressive effect should last about 1 year at which time potted plants may be repotted into fresh media.
- Use clean irrigation water.
- Avoid reusing pots from a previous crop for propagation. If pots must be reused then wash off all debris and soak in a sanitizing solution or treat with aerated steam for 30 min.
Chemical control
- Obvius (Group 4 + 7 + 11) at 4.6 fl oz/100 lb seed plus a dye. A broad-spectrum seed fungicide combination. 24-hr reentry.
Biological control Efficacy in the Pacific Northwest is unknown.
- Actinovate AG at 1 to 3 oz/as a soil drench to suppress Fusarium. 4-hr reentry. H O
- Bexfond at 7 to 14 fl oz/A. O
Reference Chef, D.G., Hoitink, H.A.J., and Madden, L.V. 1983. Effects of organic components in container media on suppression of fusarium wilt of chrysanthemum and flax. Phytopathology 73:279-281.