Divisi
Black shank
Phytophthora nicotianae · Fungal
Photo: Tashkoskip · CC BY-SA 4.0
Black shank is a soil-borne water-mould (Phytophthora nicotianae) that rots the roots and the base of the stalk in tobacco, and causes heart rot and root rot in pineapple. It thrives in warm, waterlogged, poorly-drained soil, survives for years in the ground as tough resting spores, and spreads in run-off and irrigation water, on soil-caked tools and boots, and in infested transplants — which makes it far easier to keep out than to cure.
Clemson University - USDA Cooperative Extension Slide Series , Bugwood.org · CC BY 3.0 
Tashkoskip · CC BY-SA 4.0
Why it matters
Black shank is a rot that lives in the soil and attacks the roots and the base of the stem. A bad outbreak can kill up to 9 in 10 plants (90%) — nearly your whole crop. The hard part: once this mould is in your ground it survives there for years, as tough resting specks (spores) that you cannot dig out or spray away, so it strikes again every time you plant tobacco or pineapple on that land. It spreads fastest in warm, waterlogged soil and rides from plant to plant in run-off water and on muddy tools and boots — which is why the whole battle is keeping it out and pulling the first sick plants fast, because once a stem turns black there is no cure.
When to act
Manage by prevention; wilting plants with blackened stem bases indicate established soil infection and must be rogued to slow spread.
This guidance is general, compiled from published agronomic references including FAO and CABI. Thresholds and timing shift with your crop, your variety and the season.
In much of the region a spray is simply called mushonga — medicine. But a chemical group you cannot name is one you cannot rotate, and a product you did not write down has no pre-harvest interval you can observe. Mushonga, and other farming words →
The full black shank field guide
- Identify it
- Scout for it
- Control it
16 field-guide sections in the app
The full guide to black shank — every symptom to check, how and when to walk your field looking for it, and the controls that actually work, ranked. Built into your crop plan, so you are told to look before it costs you a harvest.
Crops it affects
Frequently asked questions
How do I identify black shank?
Sudden wilting is the first thing you notice: a plant flops and its leaves hang limp as if starved of water — often in the heat of the afternoon — but unlike thirst, it does not perk up after rain or watering. The lower leaves turn yellow while the plant slowly dies.
When should I take action against black shank?
Manage by prevention; wilting plants with blackened stem bases indicate established soil infection and must be rogued to slow spread.
How do I control black shank?
PREVENT — plant a resistant variety (your single strongest tool): choose a tobacco variety bred to resist black shank and matched to the strain common in your area (your extension officer or seed supplier can point you to it). A resistant crop shrugs off the mould that would wipe out an ordinary one — nothing else you do matters as much.
Which crops does black shank affect?
Among the crops covered here: Pineapple, Tobacco.
Catch it before it costs you a harvest
Divisi builds scouting into your crop plan — it tells you when to walk your field, what to look for at that stage, and what to do when you find it. Free for farmers, works offline.
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