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Gardening glossary

Vascular wilt (verticillium and fusarium)

Vascular wilts are the silent killers of vegetable gardens. The fungi (Verticillium dahliae, V. albo-atrum, Fusarium oxysporum and related species) live in the soil for decades as resting spores. When a susceptible plant's roots grow near them, they invade through the root surface, colonise the xylem (the plant's plumbing), and block water transport. The plant cannot pull water up to the leaves and slowly wilts to death, even when the soil is moist.

The two main culprits:

- **Verticillium wilt.** Favours cool, moist soils (15–24 °C). Infects over 300 plant species including tomatoes, peppers, aubergines, potatoes, strawberries, raspberries, maples, roses, and many trees. - **Fusarium wilt.** Prefers warmer soils (24–28 °C). More host-specific — there are separate Fusarium "forma specialis" strains for tomatoes, melons, bananas, beans, peas, etc.

How to identify a vascular wilt:

1. **One-sided symptoms.** Wilt or yellowing starts on one branch, one side of a leaf, or one half of the plant. This is the most reliable diagnostic — most other problems affect the plant evenly. 2. **Older leaves yellow first.** Often in a V-shape from the leaf edge inward. 3. **Wilting during the day, sometimes partial recovery at night** — early stage only. 4. **Brown streaks inside the stem.** Slice the lower stem with a sharp knife. A healthy stem is pale green or white inside. A wilt-infected stem shows brown or dark discoloration in the vascular ring. 5. **Plant declines over weeks**, not hours. (Sudden total wilt suggests root rot, drought, or stem damage instead.)

There is no cure. Once vascular wilt is established in a plant, the plant cannot be saved. Pull and bin (do not compost) the affected plant. The fungal spores are now in your soil and will stay there for 7+ years.

Management strategies:

- **Use resistant varieties.** Look for "V," "F," "FF," or "FFF" codes on tomato seed packets — these indicate resistance to Verticillium, Fusarium race 1, race 2, and race 3 respectively. Modern hybrids like "Mountain Magic," "Defiant," and "Iron Lady" carry multiple resistances. - **Rotate crops.** Do not grow susceptible crops in the same bed for at least 4–5 years after an outbreak. - **Grafted plants.** Tomato seedlings grafted onto resistant rootstock are widely available and almost immune to soil-borne wilt on infected sites. - **Solarisation.** Covering moistened, prepared soil with clear plastic for 6–8 weeks of summer sun kills surface-layer pathogens. - **Soil drainage.** Verticillium especially is favoured by waterlogged conditions; improving drainage reduces severity. - **Container growing.** On heavily-infected sites, growing affected crops in containers with fresh sterile compost is the most reliable option.

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Related terms

Blight

Blight is rapid, widespread browning, withering, and death of plant tissue caused by fungal, oomycete, or bacterial pathogens. Unlike discrete leaf spots, blights collapse large sections of leaf, stem, or flower at once.

Leaf spot

Leaf spot is a general term for discrete, often circular lesions on leaves caused by fungal or bacterial pathogens. Spots may be brown, black, tan, or yellow-haloed and often expand or merge in humid conditions.

Anthracnose

Anthracnose is a group of fungal diseases caused mainly by Colletotrichum species, producing dark, sunken, water-soaked lesions on leaves, stems, and especially fruit. Common in beans, tomatoes, cucurbits, strawberries, mangoes, and woody ornamentals during cool, wet spring and summer weather.

Damping off

Damping off is a soil-borne fungal disease that kills seedlings within days of germination, caused by Pythium, Rhizoctonia, Fusarium, and Phytophthora species. Seedlings collapse at the soil line with a pinched, water-soaked stem. Prevention is the only real cure — by the time you see symptoms, intervention is usually too late.

Chlorosis

Chlorosis is the yellowing of plant tissue caused by reduced chlorophyll production. Common triggers include nutrient deficiency (iron, nitrogen, magnesium, manganese), high soil pH, overwatering, root damage, and viral infection.