Fusarium wilt on lemon basil (Ocimum basilicum)
Fusarium wilt on lemon basil (Ocimum basilicum); note brown streaks and spots along the stem
Fusarium wilt on lemon basil (Ocimum basilicum); note brown streaking in stem
Fusarium wilt on lemon basil (Ocimum basilicum); note healthy versus wilted plants
Fusarium wilts and rots are fungal diseases caused by Fusarium oxysporum that affect many perennial and annual plants. Whether the name wilt or rot is used can vary among plant hosts and how the disease develops. For example, the plant may exhibit signs of wilting, but the cause is a rot in the roots.
Fusarium rot can show up prior to planting as deformations in bulbs, corms, tubers, and rhizomes including blue-gray to purple-brown discoloration, spongy decay under outer scales, and occasionally white fungus and/or red-brown lesions. After planting, the disease is expressed as poorly developed root systems.
Unfortunately, the gardener usually becomes aware of the problem only after the above-ground portion of the plant is affected (wilt). Typically, initial wilting of plants in warm weather, followed by a partial recovery in the evening will be observed. The wilt will intensify and the leaves will yellow, often taking on a scorched appearance. Lower leaves are affected first and often, only one side of the plant will appear to be affected. The disease results in stunted growth and premature death of the plant.
The causal agent, Fusarium oxysporum, overwinters in soil. When conditions for its development are favorable - wet, poorly drained soil - the fungi infects plant roots. It is extremely persistent in the soil. For this reason, it is necessary to discard the plant and it may be necessary to replace or sterilize the soil.
Integrated Pest Mangement Strategies
1. Remove and discard all infected plants. When a plant dies from a root rot dig and dispose of the infected plant as quickly as is practicable.
2. Cull bulbs/corms/tubers/rhizomes. Before planting remove any shriveled, rotted, soft, and/or irregular bulbs and dispose of them in the trash. Do not compost.
3. Store bulbs properly. Thoroughly clean, dry and coat dug bulbs with a fungicide before storage and store them in a cool, dry, and well-ventilated area.
4. Plant fusarium-resistant bulbs, plants, and seedlings. If you have an ongoing problem with fusarium rot, seek out bulbs and plants that are resistant to the disease.
5. Use sterile soil-less planting mix for seedlings. Do not use garden soil or reuse potting soil when starting seeds. Disease organisms may be in the soil, which will quickly multiply in the warm, moist soil conditions needed for germinating seeds.
6. Plant rotation. Rotate plants yearly and wait at least 4 years before replanting areas contaminated with fusarium with the same plant. The population of the disease-inducing organism will decline year after year in the soil if does not have a suitable host to live on.
Strategies 1, 2, 4, 5, and 6 are strictly organic approaches.