Fusarium Wilts and Rots
Click for larger image Fusarium crown rot is responsible for the brown streaking in the vascular tissue in the stem of this tomato plant (Lycopersion); note, green pith.

Fusarium wilts and rots are fungal disease caused by Fusarium oxysporum that affects many perennial and annual plants.  Whether the name wilt or rot is used can vary amoung 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 partial recovery in the evening will be observed.   The wilt will intensify and leaves 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 grown and premature death of the plant.

Life Cycle

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.  Prevention and control of this fungus includes the following:

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 and shriveled, rotted, soft and/or irregular bulb 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, plant, 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. Populationgs of the disease organism will decline year after year in the soil if does not have a suitable host to live on.

Organic Strategies

Strategies 1, 2, 4, 5, and 6 are strictly organic approaches.

More images:

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Fusarium wilt on lemon basil (Ocimum basilicum)
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Fusarium wilt on lemon basil (Ocimum basilicum)
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Fusarium wilt on lemon basil (Ocimum basilicum); note brown streaking in stem
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Fusarium wilt on lemon basil (Ocimum basilicum); note brown streaks and spots along stem
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Fusarium wilt on lemon basil (Ocimum basilicum); note healthy versus wilted plants
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With fusarium crown rot on tomato (Lycopersicon) the roots remain white and healthy looking even though the plant is dying.
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With fusarium crown rot on tomato (Lycopersicon) vascular streaking in the stem is NOT present more than than 10 inches from the crown.
 
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