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Tobacco angular leaf spot
Pseudomonas syringae pv. tabaci · Bacterial
A warm-weather bacterial leaf disease of tobacco. It makes angular (vein-bounded) dead spots, often ringed by a wide yellow halo (the 'wildfire' form), that riddle the marketable leaf and let the plant lose grade and weight.
Why it matters
Angular leaf spot can strip up to 40% of the value off a crop. The bacteria pit the leaf with dead, angular holes and yellow halos right on the part you sell — the cured leaf loses grade, weight and price. It rides in on splashing rain and on your own hands and tools when you work the crop wet, so it can race through a field in a warm, wet week. There is no spray that cures a spotted leaf — you win by keeping it out and keeping clean leaves protected.
When to act
First small, angular (straight-edged) water-soaked spots on the lower leaves, especially after warm wet weather — act at once; a bactericide only protects clean leaves, so start before it climbs into the crop.
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 Tobacco angular leaf spot field guide
Identify it
The key sign — angular spots:
small water-soaked (greasy, see-through) spots on the leaf that dry to brown or tan dead patches with straight edges — they look angular, boxed-in by the leaf veins, not round. That vein-bounded, angular shape is the giveaway.
The 'wildfire' form
many spots carry a wide bright-yellow halo around the brown dead centre — when the crop is badly hit the yellow haloes make the field look scorched, which is why farmers call it wildfire.
As it worsens
spots run together into large dead blotches, and the dead centres may drop out, leaving ragged holes in the leaf.
Tell it apart from look-alikes
frogeye leaf spot makes round spots with a pale grey centre and a dark ring (a target/bull's-eye) — round, not angular; weather/sun scorch dries the leaf edges evenly with no greasy water-soaked start and no yellow halo; fertiliser burn follows the veins as a smooth yellowing without dead angular spots.
Scout for it
When
watch from the seedbed/nursery (INITIAL) — this is where it usually starts — right through transplanting and rapid leaf growth (DEVELOPMENT, MID_SEASON).
Watch the weather and handling
the bacteria jump on splashing rain, overhead watering, and wet hands/tools. Scout within 1–2 days after warm wet weather, and always check the seedbed before you pull seedlings.
How
walk the field in a "W" path, ~10 stops. At each stop check the lower, older leaves first (nearest the splashing soil) and look closely for the small greasy, angular water-soaked spots before they turn brown.
Threshold — act on the first spots:
as soon as you find the first angular water-soaked spots, especially after a wet spell, act — a bactericide only shields clean leaves, so start before it climbs up into the marketable middle leaves. Even a few spotted seedlings in the seedbed means: do not transplant from that patch.
Check the low, shaded, damp corners and the overhead-watered edges first
— it shows there first.
Control it
Prevent
-
start clean in the seedbed:
use clean/certified seed and a clean seedbed away from last year's tobacco. Never work seedlings or plants while they are wet, and do not water from overhead late in the day — water the soil, not the leaves, so foliage dries fast. Handle the crop as little as possible when damp.
-
starve it out of the land:
rotate — keep tobacco off the same ground for a few seasons — and remove and destroy old tobacco stalks, ratoons and volunteer plants and crop debris where the bacteria survive. Where a tolerant variety is offered, grow it.
Act early — stop the spread:
at the first spots, rogue out badly spotted seedlings in the seedbed and carry them off the field; disinfect knives/hands between plants; and hold off any operation that means handling the wet crop until it dries.
Chemical — a copper protectant, last resort:
if warm wet weather persists and spots are starting, spray a fixed-copper bactericide (the copper class your agro-dealer stocks — never a made-up brand) to shield the clean leaves, repeating about every 7–10 days while the wet weather holds. Copper only protects the surface — it cannot cure a leaf that is already spotted, so start early and keep new growth covered.
Spray safely
cover your skin, eyes, nose and mouth; spray in the cool of the day with the wind behind you; keep it off food, drinking water, children, animals and bees; respect the pre-harvest interval (the days on the label between spraying and picking); and wash well afterwards.
If it keeps spreading →
the cause is almost always handling the crop wet or overhead watering — stop both, tighten sanitation, and rogue the worst plants. Leaves already holed and haloed will not recover, so protect the clean upper leaves you still have, and after harvest clear every stalk and ratoon so it doesn't carry into next season.
Catch Tobacco angular leaf spot before it costs you the harvest
This guide is the general answer. Divisi works out yours — the week to scout your own field for Tobacco angular leaf spot, and what to do the day you find it.
Crops it affects
Plan the crops it attacks
All planting calendars, country by country
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Frequently asked questions
How do I identify Tobacco angular leaf spot?
The key sign — angular spots:. small water-soaked (greasy, see-through) spots on the leaf that dry to brown or tan dead patches with straight edges — they look angular, boxed-in by the leaf veins, not round. That vein-bounded, angular shape is the giveaway.
When should I take action against Tobacco angular leaf spot?
First small, angular (straight-edged) water-soaked spots on the lower leaves, especially after warm wet weather — act at once; a bactericide only protects clean leaves, so start before it climbs into the crop.
How do I control Tobacco angular leaf spot?
Prevent — start clean in the seedbed:. use clean/certified seed and a clean seedbed away from last year's tobacco. Never work seedlings or plants while they are wet, and do not water from overhead late in the day — water the soil, not the leaves, so foliage dries fast. Handle the crop as little as possible when damp.
Which crops are attacked by Tobacco angular leaf spot?
Among the crops covered here: Tobacco.