See:
Petunia (Petunia spp.) - Damping-off
Cause Fusarium oxysporum f. sp. callistephi, a soilborne fungus that can survive in soil indefinitely. It may be carried on garden tools, equipment, or plant roots. It survives in the soil as thick-walled, dormant chlamydospores, which 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.
Symptoms Seedlings may collapse and die. Black streaks darken vascular tissue up one side of older plants. Plants wilt regularly before dying. Root production is greatly reduced, and a dark colored root rot may be observed. In wet weather, salmon-color spore masses may form on infected stems. If infected plants live long enough they tend to mature earlier, have sterile seeds heads or few seeds with low viability.
Cultural control
- Rotate plantings in the landscape.
- Do not use debris of affected plants as mulch or organic matter for pathogen-free soil.
- Plant in soilless potting mix with a 6 to 6.6 pH.
- Germinate seed in a soil temperature between 70°F to 72°F.
- Destroy infected plants.
Chemical control Drench beds at seeding or transplanting. Not effective as a sole treatment but must be integrated with cultural controls. Use these materials preventively only at seeding or transplanting. Do not use to salvage the crop, as treatments are generally ineffective and only help increase the risk of developing resistant fungi.
- Banrot 40 WP at 4 to 8 oz/100 gal water. Group 1 + 14 fungicide. 12-hr reentry.
- Heritage at 1 to 4 oz/100 gal water plus a non-silicone-based wetter sticker. Group 11 fungicide. 4-hr reentry.
- Medallion WDG at 1 to 2 oz/100 gal water. Using with oils or adjuvants may damage plant. Group 12 fungicide. 12-hr reentry.
- Terraguard SC at 4 to 8 fl oz/100 gal water. Group 3 fungicide. 12-hr reentry.
Reference Olsen, C.M. 1965. A fusarium wilt of tagetes marigolds. Phytopathology 55:711-714.