Quck answer
Black mold on citrus trees can be killed by following these steps:
1. Trim affected branches: Remove any branches or leaves that show signs of black mold.
2. Prune properly: Make clean cuts and dispose of infected material away from the tree.
3. Apply fungicide: Use a fungicide specifically designed to kill black mold on citrus trees.
4. Follow instructions: Read and follow the instructions on the fungicide label carefully.
5. Repeat if necessary: If the mold persists, repeat the process until it is completely eliminated.
6. Prevent future infestations: Maintain proper tree hygiene, provide adequate sunlight and air circulation, and avoid overwatering to prevent future mold growth.
If you have noticed a dark fungus on the leaves of your lemon tree (Citrus limon, USDA zones 8 to 11) or your other citrus trees (Citrus spp., USDA zones 8 to 11), it means that your plants are covered in sooty mold. When you take a closer look at your plants, you will probably see small pests like aphids or whiteflies; these pests are the cause of the sooty mold. While sooty mold usually does not harm or kill your citrus trees, it can be unpleasant to look at. You can remove the mold from the citrus leaves, but controlling the pest outbreak will prevent the formation of sooty mold in the first place.
Characteristics of Sooty Mold
Sooty mold is most commonly caused by fungi belonging to the genera Scorias, Capnodium, and Fumago. It gets its name because it looks like a layer of black soot covering parts of the citrus plant. Sooty mold is often found on citrus fruits, small branches, leaves, and twigs. An outbreak of sooty mold results in black spots on lemon tree leaves and leaves of all types of citrus.
If you see sooty mold on your citrus, it means that you have a problem with pests such as aphids and whiteflies. These pests have sucking mouthparts and feed on the sap of the plant. After feeding, they excrete a sticky, sweet substance called honeydew, which is what the sooty mold grows on. When sooty mold appears, it usually indicates a large population of these sucking insects infesting your citrus tree.
Although sooty mold usually does not harm or kill your citrus plants, a widespread outbreak can interfere with photosynthesis. Reduced photosynthesis leads to delayed fruit coloring, stunted growth, and leaf drop. You can control sooty mold by controlling the insects that cause it, but a small amount of sooty mold will not harm the tree. Alternatively, you can remove it by spraying the affected area with water or washing off the affected parts with soap and water.
Controlling Aphids that Cause Sooty Mold
Aphids are small, pear-shaped insects that reproduce asexually, so their populations can quickly infest citrus trees. They feed on new foliage growth, resulting in stunted and distorted leaves, including leaves that are cupped, twisted, or curled. They cause the most damage to young citrus trees.
Common aphids found on citrus trees include brown citrus aphids, black citrus aphids, green citrus aphids, and cotton aphids. These pests are black, brown, green, or pale yellow in color and gather in large populations on the leaves and branches. An indication that you have aphids is when you find ants traveling along the branches to reach the aphids, which they “milk” to extract the honeydew.
If the aphid population infesting your citrus trees is small, natural predators like ladybugs or ladybird beetles will usually take care of the problem. However, if the aphid population has become uncontrollable, you can eliminate them by saturating the pests with insecticidal soap. Products like neem oil and horticultural oils also kill the pests, but make sure to follow the instructions on the label for proper application.
Managing Sooty Mold Caused by Whiteflies
Sooty mold is a common problem caused by whiteflies, which are insects that feed on citrus plants by sucking sap. The adult whiteflies lay their eggs on the underside of the leaves, and the eggs hatch into transparent nymphs. There are different types of whiteflies that infest citrus, such as the citrus whitefly, cloudy-winged whitefly, bayberry whitefly, and wooly whitefly.
Natural predators, including lady beetles, parasitic wasps, fungi, and lacewing larvae, help control whitefly populations on citrus plants. In most cases, insecticides are not necessary to control whiteflies. However, if the whitefly population is increasing, using horticultural oil can be effective in eliminating both the pests and their larvae. It is important to carefully follow the instructions on the product label when applying insecticides.
