Tobacco brown spot

round brown spots on the older, lower leaves, usually 1 to 3 cm across (about the size of a fingernail to a large coin). Look closely and each spot has rings inside it, one inside the other, like a target or an archery board (this is 'target spot'), and each spot is ringed by a yellow halo where the green fades. It always starts low down, on the oldest, most ripe leaves first — not on the young top leaves.

the spots grow, join up and dry out, and the papery dead centres crack and fall out so the leaf looks shot full of holes and tears easily. It is worst on over-ripe leaf left too long on the plant, and after warm, humid, dewy weather you may find dozens of spots on a single bottom leaf.

picked leaf that goes in damp or already spotted keeps rotting during curing — spots spread and the leaf goes brown and brittle. This 'barn rot' is the same fungus carrying on indoors.

with frogeye leaf spot, whose spots are smaller with pale grey or white papery centres and a dark brown ring, but NO target rings inside. Also not angular leaf spot (a bacterial disease) — those spots are angular and water-soaked, boxed in by the leaf veins, with no rings and no yellow halo. And not weather fleck / ozone injury, which is fine white-to-brown speckling scattered over the top leaves with no round spots and no halo. Brown spot is the one with round target rings and a yellow halo, low on the oldest leaves.

from topping and the start of ripening onward — the mid-season and late-season stages — because that is when the lower leaves begin to age and ripen, which is the only leaf this weak fungus can attack. Step up your checks the moment the weather turns warm and humid, or after rain, mist or a heavy dew, since those wet nights are when the spots multiply.

every few days walk a big "W" shape so you cross all four corners and the middle — not just the row nearest the path. Make about 10 stops along the way.

look at the lowest, oldest, most ripe leaves first (turn a few over too), hunting for the round target-ring spots with the yellow halo. Those bottom leaves ripen and age first, so that is where brown spot always shows up first.

the very first target-ring spots on the ripening lower leaves are your signal to pick those leaves promptly — do not wait for them to over-ripen. If spots are showing on the lower leaves of about 1 in every 10 plants (10%) while the weather stays warm and humid and the leaf is not yet ready to pick, that is the point to start protectant sprays to protect the leaf still on the plant.

the moment you find spotted lower leaves, pick and remove them — take the ripe ones to cure and destroy (bury or burn) any that are too rotten to use, well away from the field and the barn. Getting the diseased leaf off the plant and out of the crop cuts down the spores that would spread to the leaf above.

if warm, humid weather is holding and spots are appearing before the lower leaves are ready to pick, use a protectant (contact) fungicide such as mancozeb. "Protectant" means it coats the leaf and stops new spores taking hold — it shields healthy leaf but cannot cure a spot already there, so it must go on before or at the very first spots and be re-applied on a regular schedule (about every 7 to 10 days) through the humid spell and after rain washes it off.

cover your skin, eyes, nose and mouth; spray in the cool of the morning or evening with the wind at your back; keep the spray off drinking water and rivers, and away from children and bees. Respect the pre-harvest interval — the number of days the label says you must wait between the last spray and picking the leaf — this matters doubly for tobacco because the leaf is cured and smoked. Wash yourself and your clothes afterwards.

do not lean on one product forever — rotate to a fungicide from a different chemical group each time so the fungus cannot get used to it. Protectant sprays like mancozeb used before symptoms are the backbone; never rely on a single product spray after spray.

when the lower leaves are spotting faster than you can hold, pick the ripe and lightly-spotted leaves early rather than losing them to over-ripening, and keep them apart from clean leaf. Cure with plenty of ventilation and never load damp or wet leaf into the barn, because the fungus carries on rotting leaf indoors. When grading, sort brown-spotted leaf out into its own lower grade — one rotten leaf packed with good leaf pulls the whole lot down.