Symptoms of sooty mold
In summer, the plant has black carbon deposits, like soot, on its foliage. On closer inspection, on and under the leaves, around the stems, we notice sticky drops and the presence of small insects (mealybugs or aphids generally). It is sooty mold.
Description and consequences for the plant
The sooty mold is a cryptogamic disease, that is to say that the infectious agent is a filamentous fungus, of the family of ascomycetes. The spores, either of "Capnodium oleaginum" or of "Fumago salicina" are transported by insects or the wind. They are deposited on the honeydew, which serves as a substrate for their development. The honeydew is a sticky and sweet substance, coming from the accumulation of excretions of these insects "sucking-biting" sap. They can be aphids, scale insects, but also psyllids, whiteflies, thrips or leafhoppers. The plant is already weakened by the primary pest attack. The sooty mold, secondary disease, can cause suffocation of the concerned plant. Indeed, the blackish layer on the leaves, apart from its unattractive side, prevents light from entering the cells, which slows photosynthesis. The growth process is greatly slowed down.
Control of sooty mold
It is first necessary to clean the leaves, that is to say remove as much of this black felting and honeydew. This is easily done with your finger or with a cloth, as the fungus only develops in the honeydew outside the plant. But that is not enough, the fight against "sucking and biting" insects is necessary to eliminate the presence of honeydew. It is therefore necessary to treat, "biologically" if possible, parasitic insects, with black soap, nettle liquid or a product based on natural pyrethrum. The treatment should be done late at night or very early in the morning, while the bees are in the hive, as they too are fond of honeydew.
Prevention of sooty mold
A well-nourished plant of regional species will be more resistant to parasitic attacks. It is necessary to diversify the species and to privilege the alternation of the cultures, favorable to the auxiliary insects (ladybugs, parasitic wasps, lacewings…).
Plants affected by sooty mold
The sooty mold grows on a large number of plants: camellias, rhododendrons, oleanders, olive trees, hydrangeas, roses, citrus fruits and other fruit trees… By C. Schutz Croué