Black shank of tobacco
Sudden wilt with a blackened, rotting stem base and dark disc-like plates across the pith — a soil water-mould that thrives in wet, badly drained tobacco land.
- Pathogen
- Water-mould (Phytophthora nicotianae)
- Spreads by
- Soil, irrigation & run-off water, infected seedlings, tools
- Favoured by
- Warm, wet, poorly drained soil; short rotations
- Main risk
- Whole plants wilt and die; patches spread fast
Overview
Black shank is caused by the soil-borne water-mould Phytophthora nicotianae. It is the single most damaging soil disease of tobacco worldwide and in the Indian FCV tracts, and once a field is infested the pathogen stays in the soil for years as thick-walled resting spores (chlamydospores and oospores). It can strike from the seedbed to just before harvest, but the heaviest losses come on the main-field crop after transplanting.
The fungus first rots the fine roots, then moves up into the stem base, where it produces a soft brown-to-black rot that girdles the "shank" at and just above the soil line. Above ground the plant wilts — often one side first — yellows, and collapses, and the wilt can run through a low, wet patch of the field in a few days after irrigation or rain. Split a dead stem lengthwise and the pith is broken into a stack of dark, dried, disc-like plates, a sign that separates black shank from Fusarium or bacterial (Granville) wilt. Management is built on resistant varieties, long rotation away from tobacco and other hosts (chilli, tomato, brinjal), sharp field drainage, and clean nursery practice; fungicides only support these.
How to identify it
- Sudden wilting of the whole plant, sometimes one side first, that does not recover overnight.
- A soft brown-to-black rot girdling the stem base at and just above the soil line, sometimes creeping up the stalk.
- Split the stem lengthwise: the pith is broken into a stack of dark, dried, disc-like plates with gaps between them.
- Black, rotted roots, and plants pulling up easily.
- Wilt and death spreading in patches, worst in low, wet, poorly drained parts of the field, and fastest after irrigation or heavy rain.
What causes it and when
- The soil-borne water-mould Phytophthora nicotianae, which survives for years in the soil as resting spores and in infected crop debris.
- Favoured by warm soil (28–32°C), free water and waterlogging, heavy clay or compacted soil, and repeated tobacco or chilli/tomato/brinjal on the same land.
- Swimming spores (zoospores) are carried to fresh roots in soil water, irrigation water and field run-off, and on muddy implements, feet and seedling roots.
- Can appear in a wet seedbed but does most damage on the main-field crop from a few weeks after transplanting onward.
Cultural & organic control
- Grow a black-shank-resistant or tolerant variety recommended for your tract — the single most effective measure where the disease is established.
- Rotate for at least 2–3 years (longer on badly hit land) with a non-host such as a cereal, sorghum or a grass, and keep chilli, tomato and brinjal out of that rotation.
- Get the water off the field: ridge and plant on the ridge, open deep field drains, break any hardpan, and never let water stand.
- Raise seedlings on a raised, well-drained, clean or solarised seedbed; discard any seedling with a discoloured stem or root, and do not carry nursery soil into the field.
- Rogue wilting plants early with the soil around the roots, carry them out of the field and destroy them; do not irrigate from a pond that drains an infected field.
- Deep-plough after harvest to bury debris, and apply Trichoderma through farmyard manure as part of the package.
Chemical control
- Drench the seedbed and, after transplanting, the base of the plants with a CIB&RC-registered oomycete fungicide (metalaxyl / metalaxyl-M + mancozeb, or fosetyl-Al) where recommended for tobacco in your state.
- Repeat the drench after a spell of heavy rain or a flood irrigation, when a fresh flush of infection is most likely.
- Treat the soil around a roguing gap before replanting or gap-filling.
- Fungicides only slow the disease — they do not clear an infested soil, so use them on top of a resistant variety, rotation and drainage, never instead of them.
- Confirm the current product, dose and pre-harvest interval for tobacco with your KVK or the Central Tobacco Research Institute (CTRI).
Prevent it coming back
- Make a resistant variety, a long non-host rotation and ridge planting with hard drainage the standard on any field that has ever shown black shank.
- Keep the nursery clean and well-drained every year, and never move soil, water or seedlings from an infected field to a clean one.
- Map the patches where plants wilted this year and watch them first next season.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Varieties to consider
Named seed varieties whose resistance or susceptibility to this problem is documented on their own variety page.
Frequently asked questions
My tobacco plants are wilting and the stem base has gone black and soft. What is it?
That is black shank, caused by the soil water-mould Phytophthora nicotianae. It rots the roots and then blackens and girdles the stem base, so the plant wilts and dies, often within a day or two of irrigation or rain, and the wilt spreads in patches through wet parts of the field. Split a dead stem lengthwise — if the pith is in dark, dried, disc-like plates it confirms black shank. Rogue affected plants with their soil, improve drainage at once, and plan a resistant variety and a long rotation for next season.
How is black shank different from Fusarium wilt in tobacco?
Both cause wilting, but black shank rots and blackens the outside of the stem base and leaves the pith in disc-like plates, and it spreads fast in wet patches after irrigation. Fusarium wilt usually browns the water-conducting tissue (a ring of discolouration when you cut the stem across), is often one-sided, and is worse in warm dry spells. Confirm with your KVK, because the resistant varieties differ.
Can I grow tobacco again on a field that had black shank?
Yes, but only with a black-shank-resistant variety, after 2–3 years (more on badly infested land) under a non-host crop such as a cereal or sorghum, and with the drainage fixed so water never stands. Plant on ridges, keep the nursery clean, drench at the base where recommended, and rogue any early wilters. Without the resistant variety and the rotation, the disease will build straight back up.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.