Fusarium wilt on Plants

Symptoms

Fusarium wilt often shows up on one side of a plant before the other side shows any change. The leaves turn yellow, wilt, then brown, and they eventually die. Older leaves tend to discolor and wilt first, and the whole plant can die as the disease moves through it. If you cut through the base of an infected stem, you may see brown rings inside. Dead tissue sometimes grows small pink, cushion-like masses made up of spore-bearing stalks. In seedlings, the disease can kill the young plant outright. In older plants, black streaks darken the vascular tissue, running up one side of the stem. Dig up a struggling plant and you may find a root system that is rotted and much smaller than it should be. During wet weather, infected stems can develop spore masses with a salmon color. These symptoms appear across many hosts, including tomato, dahlia, and gladiolus. Watch for several of these changes together, since more than one often appears on the same plant.

Causes

The fungus Fusarium oxysporum causes this disease, surviving in soil for years as tough resting spores called chlamydospores. The fungus enters a plant through its small rootlets. Warm temperatures help the fungus spread, both inside a plant and from plant to plant. Soil that drains poorly raises the risk of infection. Too much irrigation pushes roots to grow shallow near the surface, where they are more exposed to the fungus. Heavy fertilizing, especially with urea, also raises the risk of this disease. Many plants can host this fungus, including tomato, dahlia, gladiolus, and date palm. Avoiding undecayed organic matter around host plants is one way growers try to limit the fungus's spread. Infected plants may be destroyed to keep the fungus from spreading to healthy ones nearby. Soil solarization before planting may also lower the chance that new plants become infected. Growers who destroy infected plants aim to stop the fungus from spreading further. Promptly removing infected plants is another way to reduce spread to nearby hosts.

Diagnosis

A one-sided pattern of wilting is one of the clearest signs of Fusarium wilt. Cut into the base of a stem and look for brown rings inside the tissue. Pink, cushion-like masses of spore-bearing stalks on dead tissue point to this disease as well. During wet weather, check stems for salmon-colored spore masses, another sign to look for. Dig up the roots and check whether the root system looks rotted and smaller than normal. In older plants, look for black streaks running up the vascular tissue on one side of the stem. Seedlings that die suddenly may also point to this fungus. Warm conditions that favor the fungus's spread can make symptoms develop and worsen faster. Comparing both sides of the plant can help you spot this one-sided pattern. This fungus infects plants through their rootlets. Many hosts, such as tomato, dahlia, and date palm, can show this same set of symptoms. Poorly drained soil is another factor linked to this disease. Overirrigation, which leads to shallow surface rooting, is another contributing factor to watch for.

Treatments

If a plant has died from Fusarium wilt, avoid replanting that spot with another plant from the same genus. Instead, choose a species from a different genus for that location. Where resistant cultivars exist for your plant species, grow one of those instead. Buy new plants from a reliable, high-quality source. Avoid poorly drained soil, and plant on mounds or raised beds instead. Give plants good growing conditions and proper care overall. Do not overirrigate, since too much water encourages shallow, surface rooting. Avoid using undecayed organic amendments around Fusarium hosts. Avoid excessive fertilizing, especially with urea. Keep mulch, debris, and other plants away from the base of hosts, especially palms. Remove and dispose of infected plants promptly to reduce spread to nearby hosts. In some cases, growers destroy infected plants outright. Soil solarization before planting may reduce or delay infection in plants set out afterward. Use a potting mix that is free of the pathogen. Fusarium oxysporum survives in soil for years as chlamydospores. Many ornamental and vegetable hosts are affected, including chrysanthemum, dahlia, tomato, and watermelon. Symptoms often appear first on one side of the plant. The fungus infects plants through their rootlets. Warm temperatures favor the fungus's spread within and between plants. Pyracantha and date palm are among the woody hosts affected by this fungus. Tomato and watermelon are among the vegetable hosts at risk.

Prevention

Avoid overirrigating, since too much water pushes roots to grow shallow near the surface. Skip heavy fertilizing, especially with urea. Plant in soil that drains well, or use mounds or raised beds if drainage is poor. Keep mulch and other plant debris away from the base of host plants, especially palms. Choose a planting site you have not used for a host from the same genus before. Start with new plants from a reliable, high-quality source. Use a potting mix that is free of the pathogen. Soil solarization before planting may reduce or delay later infection. Grow resistant cultivars where they are available for your plant species. Remove and dispose of infected plants quickly to limit spread to healthy ones nearby. Providing a generally good growing environment with proper care also helps prevent problems.

Plants most often affected

This disease affects a wide range of plants, from woody ornamentals to common vegetables. Woody hosts include albizia, date palm, hebe, and pyracantha. Herbaceous ornamentals at risk include aster, carnation, chrysanthemum, cyclamen, daffodil, dahlia, freesia, and gladiolus. Vegetable hosts include asparagus, bean, cabbage, cantaloupe, pea, tomato, and watermelon.

• Balsampear
• Cabbage
• Carnation
• Coriander
• Daffodil
• Garden Lettuce
• Garden Tomato
• Purple Granadilla
• Silktree
• Sweet Basil
• Wild Celery