Mango Problems: Anthracnose on Flowers and Fruit, Hoppers and Powdery Mildew

Anthracnose: the disease that decides the crop

Wherever it rains during flowering, anthracnose is the reason mango crops fail. The fungus survives the dry season quietly in dead twigs, old flower stalks, mummified fruit and even in apparently healthy leaves, and it needs only free water on the plant surface to release spores and infect. Rain, prolonged dew and overhead irrigation all provide it.

On the panicle it shows as small dark brown to black specks on the flower stalks that spread and run together, until the whole branch of the spray turns black and dries. Flowers drop before they can be pollinated, and a heavily infected panicle sets nothing at all. This is the single largest cause of a tree that flowers beautifully and produces no fruit.

On leaves it produces dark angular spots, often along the margins, which dry and drop out to leave ragged holes. On young fruit it causes black lesions and drop. On the fruit that survives, it does something more insidious: it infects while the fruit is small and green, then goes dormant. Nothing is visible at harvest. The lesions appear as the fruit ripens, as sunken dark spots that spread and rot the flesh underneath, often within a couple of days of the fruit softening. Fruit that looked perfect off the tree turns spotted on the kitchen counter.

The consequence for the gardener is that the control has to happen before the damage exists. Once the panicle is black, or the ripening fruit is spotted, there is nothing left to do about that crop.

Getting ahead of anthracnose

Everything useful is done before and during flowering, and most of it is not spraying. The aim is to reduce the spore load in the tree and to shorten the time the panicles stay wet. On a garden tree with a modest crop, sanitation and canopy management alone make a large difference, and in a dry flowering season they may be all you need.

Where spraying is warranted, timing is what matters. Applications from the moment the panicle emerges through to fruit set, repeated every week to fortnight while wet weather continues, protect the flowers. Copper-based products are the usual garden option and are effective if applied before infection rather than after. Check what is permitted for edible crops where you live and follow the label; nothing here replaces that.

1. Clean out the inoculum after harvest Cut out dead twigs, remove every mummified fruit still hanging in the canopy, and rake up and dispose of fallen leaves, old panicles and dropped fruit. Do not compost this material near the tree. This is where next season's spores are living.
2. Open the canopy Prune to let air and light through the center so foliage and panicles dry quickly after rain. A dense canopy holds dew until mid-morning, which is exactly the window the fungus needs.
3. Stop wetting the leaves Water at the ground with a hose, a soaker or drip. An overhead sprinkler running through flowering creates infection conditions every evening regardless of the weather.
4. Protect from panicle emergence If you spray, begin as the panicles push out and repeat every seven to fourteen days through flowering and early fruit set while conditions stay wet. Applying after the panicle has blackened achieves nothing.
5. Cover small trees while they flower On a containerised or small tree, keeping rain off the open panicles with a cover set clear of the canopy is more effective than any spray, and it solves the pollination problem at the same time.
6. Handle the fruit as if it is already infected Ripen harvested fruit spread out in a single layer with air around each one, not piled in a bowl. Latent infections spread fastest in a warm humid heap, and one rotting fruit takes the others with it.

A hot water dip of harvested fruit, around 122F (50C) for five minutes, is the standard commercial treatment for latent anthracnose and it works at garden scale too. Use a thermometer; too hot scalds the skin and too cool does nothing.

Hoppers, powdery mildew and the other panicle pests

Mango hoppers are small wedge-shaped insects that cluster on the flower panicles and young shoots and suck sap. In numbers they cause flowers to dry and drop, and they excrete honeydew that a black sooty mold then grows on, coating leaves and stalks in a dark film that blocks light. You usually notice the mold and the stickiness before the insects, and you can confirm them by tapping a panicle over a sheet of paper and watching them scatter sideways.

Powdery mildew is the other flowering-season disease, and unlike anthracnose it prefers dry, cool conditions with heavy dew, so the two swap places from year to year. It appears as a white or grayish powdery coating on panicles, young fruit and the undersides of new leaves, and infected flowers dry and drop. Sulfur-based products control it well, but do not apply sulfur in hot weather or within a fortnight of an oil spray.

Fruit flies attack ripening fruit, laying under the skin so the flesh breaks down around a tunnel of maggots and the fruit drops. Bagging individual fruit once they reach a couple of inches (5 cm) is the reliable garden control, and it protects against sunburn and bird damage at the same time. Collect and destroy every dropped fruit; leaving them on the ground breeds the next generation.

Scale insects, mealybugs and thrips all appear on mango and are generally secondary. Ants farming scale for honeydew are worth interrupting with a sticky band on the trunk, because removing the ants lets predators do most of the work for you.

Keep a short record of what appeared and when, panicle by panicle: the date the first black stalk showed, the date mildew appeared, the weather that week. Because both diseases must be prevented rather than cured, last year's dates are what tell you when to start this year.