Tomato
Damping-Off of Seedlings
Pythium spp.
Fungus
In a Nutshell
- Seeds rot in the soil.
- Water-soaked, dark lesions at the base of seedling stem.
- Light mold-like growth covers seedlings.
Tomato
Symptoms
Damping-off can occur in two phases during seedling development, during pre-emergence or post-emergence. In the pre-emergence phase, the fungus colonizes the seeds just after sowing, causing seed rot and stopping germination. In the post-emergence phase, seedlings grow poorly and the base of the stem starts to rot. The stem is visible as soft and slimy with water-soaked, grey, brown or black lesions. Young plants or trees become chlorotic and start to wilt, eventually toppling down, appearing as if they have been cut off at the base. White or grey mold-like growth appears on dead plants or on the soil surface. When seedling loss is extensive, replanting may be necessary.
Recommendations
Organic Control
Biofungicides based on fungi Trichoderma viride, Beauveria bassiana or the bacteria Pseudomonas fluorescens and Bacillus subtilis can be used as seed treatment or applied around the root zone at the time of planting to prevent or control the pre-emergence form of damping off. In some cases, the preventive treatment of seeds with copper fungicides such as copper oxychloride or Bordeaux mixture help to reduce the incidence and severity of the disease. Homemade solutions based on plant extracts of Eupatorium cannabinum completely inhibit the growth of the fungus.
Chemical Control
Always consider an integrated approach, using both preventive measures together with biological treatments if available. Preventive measures and careful conduct during field work are the best way to avoid the disease. In fields with histories of damping-off or problems with drainage consider using fungicides as preventive measure. Seed treatments with metalaxyl-M can be used to control the pre-emergence form of damping-off. Using foliar spray with captan 31.8% or metalaxyl-M 75% during cloudy weather may also help. The soil or the base of the plant can be drenched with copper oxychloride or captan every fortnight from the time of planting.
What caused it?
Damping-off can affect several crops and is caused by fungi of the genus Pythium, which can survive for several years in soil or plant residues. They thrive when weather is warm and rainy, soils are excessively moist and plants are densely sown. Stressful conditions, such as water-logging or high nitrogen application, weaken the plants and also favor the development of the disease. Spores are disseminated via contaminated tools or equipment and mud on clothes or shoes. Event though they can attack crops during their whole life cycle, germinating seeds or young seedlings are more susceptible. The disease is not necessarily carried over from one season to another in the same place, but rather appears when and where conditions favor infection.
Preventive Measures
- Use seeds from healthy plants or from certified sources.
- Use resistant varieties if available.
- Use raised beds in sites with poor drainage or with wet soils.
- Keep a wider space between seeds or seedlings at planting to favor the drying of the canopy.
- Do not plant seedlings too deep when transplanting.
- Remove infected plants as the first symptoms appear.
- Plan a balanced fertilization with split nitrogen applications.
- Water regularly but superficially.
- Water early in the morning so that the soil surface is dry by evening.
- Adopt the ring method of irrigation so that the water does not come in direct contact with the stem.
- Take care not to inadvertently transport mud from one field to another.
- Thoroughly disinfect tools and equipment, with household bleach for example.
- Remove and destroy plant residues after harvest.
- Plan a crop rotation with non-susceptible plants.
- If possible, expose seedbed soils to solar radiation with a plastic mulch.
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