How to prevent and control mango sooty mould? Be sure to guard against this disease when growing mangoes

In recent years, mango sooty mould has caused increasingly serious damage to mango fruit, greatly affecting fruit quality. Below is a brief introduction to the symptoms and damage of sooty mould, the occurrence of the disease, and control methods, for the reference of fellow fruit growers.

1. Symptoms and damage. Sooty mould mainly damages mango fruit, and also has a certain effect on branches and leaves. When the fruit grows to the size of a fist, a small number of tiny black spots can be observed on its surface, as if smeared with a little soot; this is the initial sign of fruit infection. As the fruit gradually grows, the black spots expand and form a black dirty patch; usually the black dirt develops from the fruit stalk toward the middle of the fruit. When the fruit surface is dry, it is very difficult to wipe off the black dirt; if the contaminated fruit is soaked in water for several minutes, the black dirt can be gently washed off with a damp gauze. It should be especially noted that this disease only affects the fruit skin and does no direct harm to the flesh. Affected fruit has a poor appearance; in severe cases, the entire peel turns black as if painted with black ink, greatly reducing its commercial value. The effect of sooty mould on leaves is mainly to reduce photosynthesis on the leaf surface, but according to the author's observations of several orchards in the county in recent years, the effect of this disease on leaves is not very great.

2. Occurrence of the disease. (1) Natural environmental factors. The elevation of the orchard, the degree of ventilation, and the light all have a close relationship with the degree of sooty mould occurrence. Generally speaking, if the orchard is high in elevation, the fruit trees are widely spaced, ventilation and light are good, there are few weeds on the ground, and the relative humidity of the orchard microclimate is low, then the disease is mild; otherwise it is severe. (2) Pest factors. The black dirt on the fruit surface is actually a large amount of sooty mould fungi. The honeydew secreted by homopteran insects (scale insects, leafhoppers, aphids, red spider mites, etc.) sticks to the branches, leaves and fruit surface; the honeydew is rich in various organic substances needed for the growth of sooty mould, providing an environment for the massive reproduction of sooty mould. When rain comes, the honeydew flows down along the water, and the sooty mould develops downward with it, forming what is commonly called the “mango shedding tears” phenomenon.

3. Control methods. (1) After harvesting the fruit each year, prune the fruit trees promptly, cut off dead leaves and old leaves, gather the cut branches and leaves into piles, and burn them. Regularly clear weeds in the orchard, especially during the flowering and fruiting periods, when weeds should be actively removed; dead grass should be burned or buried. Regularly control homopteran insects, with special attention to scale insects (the common one being the elliptical scale), because adult scale insects have a waxy scale covering their bodies and are relatively resistant to pesticides, so spraying is only effective during the nymph stage before their scale covering has formed. The nymph stages of scale insects are in mid-May, mid-to-late July, mid-to-late September, and early October. Seize these periods and spray with 40% omethoate emulsifiable concentrate at 1000 times dilution. Scale insects mostly hide on the underside of leaves, so attention should be paid to this when spraying pesticides. (2) Control of sooty mould. You can use 30% copper oxychloride suspension concentrate at 800 times dilution and 70% thiophanate-methyl wettable powder at 800 times dilution for spraying, or spray Copper Master. Experiments have shown that the latter two have better effects. In theory, it is best to spray once every one to two months; if conditions do not permit, spray once each during the flowering period and the fruiting period, but the effect will be slightly poorer.