Yam anthracnose

small dark brown to black spots on the leaves, each about the size of a pinhead to a match-head. Look closely and many have a pale or yellowish edge around the dark centre.

the spots grow and join into large blackened patches, and the leaf looks scorched. On the stems and leaf-stalks you'll find sunken dark streaks and lesions - the surface dips in, like a healed-over cut.

whole shoots turn black and die from the tip back, leaves shrivel and drop, and the vine can be left as bare blackened stems with almost no leaves - this is the stage that starves the tuber.

in rainy, humid weather the fungus is most active and the lesions look dark and fresh; in dry spells the dead patches look papery and grey-brown.

with plain drought scorch (which browns leaf edges and tips evenly, with no dark spots or sunken stem lesions) or with old insect chewing (which leaves holes and torn edges, not sunken black streaks). Anthracnose gives you spots + sunken stem lesions + shoot dieback together.

start checking as the vines are climbing and filling out in the development and mid-season stages - the growing, leafy period when the tubers are bulking and the disease does most harm. Look hardest during and just after rainy, humid spells, which is when it takes off.

once a week in the wet season, walk a large "W" across the plot so you cover all four corners and the middle, not just the plants beside the path.

stop about 10 times along your walk and look over 10 vines at each stop. Check the lower, shaded, crowded leaves first (they stay wet longest), then the leaf-stalks and stems, then the growing shoot tips for any blackening.

if you find dark leaf or stem lesions on even 1 in 10 vines during rainy weather - especially on a variety you know is prone to it - treat that as your trigger to act now, before it jumps across the wet canopy. Don't wait for dieback; by then much of the damage is done.

note where you first saw it. The disease spreads outward from these starting points, so those are the plants to watch and the trash to clear first.

as soon as you spot early lesions, cut off and destroy the affected leaves and shoots (burn or bury them, well away from the plot). Taking out the first hotspots slows the spread across the canopy.

on a high-value crop, or when it keeps spreading despite the steps above, spray a protectant fungicide of the mancozeb group. "Protectant" means it coats the leaf and stops new infection - it does not cure spots already there - so spray at the first symptoms and cover the new growth, repeating during wet spells as the label directs.

cover your skin, eyes, nose and mouth; spray in the cool of the day with the wind at your back; keep it off food, drinking water, children and bees; respect the pre-harvest interval (the number of days the label says you must wait between the last spray and eating or selling); and wash yourself and your clothes afterwards.

don't lean on the same chemical every time - rotate to a different fungicide group between sprays so the fungus can't build up resistance, and remember spraying only works alongside clean material, staking and sanitation, not instead of them.

tighten the basics - remove more infected vines, improve staking and spacing, and keep the protectant cover on the new growth through the wet spell. When a plot is already stripped to bare blackened stems, it's too late to save that vine - cut your losses, harvest what tubers you can, and clear and destroy every old vine so the disease doesn't carry over. Next season, start clean: tolerant variety, healthy setts, wider spacing, and rotate the plot.