Papaya
Sooty Mold
Pezizomycotina
Fungus
In a Nutshell
- Dark grey to black mold on fruits.
- Leaves, twigs and stems can also be affected.
- Leaves may die and fall off.
Papaya
Symptoms
Sooty mold can be found on mango trees and any other plants that have previously been fed upon by insects. The mold grows on honeydew, a sticky, sugary secretion that is produced by some insects to attract fellow bugs. Using the honeydew as a food source, the mold gradually covers the surface of the affected plant part, coloring it in various shades of black. Sooty molds are non-parasitic and non-pathogenic fungi, so they do not colonize plant tissues or trigger symptoms. However, they alter the ability of the plant to perform photosynthesis and to exchange gases with the atmosphere. Severely infected leaves may die and fall off, thereby affecting the plants growth and survival.
Recommendations
Organic Control
Use formulations of neem oil, which is an organic broad spectrum compound, to ward off whiteflies, aphids, scales, ants, and mealy bugs. Neem oil also reduces the growth of the fungus itself. Insecticidal soap or dish soap (e.g. one tablespoon per 5 liters of water) can be sprayed on affected plants. After letting the soap solution settle on the plants, it can be rinsed off, thereby removing the mold.
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatments if available. Synthetic insecticides of the organophosphate family can be used to prevent insects from feeding on the plant.
What caused it?
Phloem-feeding insects like the mango leafhopper (Amritodus atkinsoni), whiteflies, aphids and many others are associated with the disease as they feed on plant sap. In the process of feeding, honeydew is secreted on the surface of the plant, thereby creating the perfect medium for sooty mold to grow on. Honeydew can drip down on neighboring leaves or plants, thus spreading the fungus further. The fungi survive as mold or as spores on plant parts, tools or transport vehicles. Insects also spread the mold from plant to plant. Ants, for example, tend to protect the sooty mold colonies for their own benefit.
Preventive Measures
- Make sure to provide enough distance between the plants or trees and sufficient sunlight.
- Build physical barriers around trees or plants to prevent ants and plant sap-sucking insects from reaching them.
- Fertilize and water the trees sufficiently to ensure an optimal natural resistance of the trees to phloem-feeding parasites.
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