By: Mary H. Dyer, Credentialed Garden Writer
Citrus sooty mold isn’t actually a plant disease but a black, powdery fungus that grows on branches, leaves, and fruit. The fungus is unsightly but it generally does little harm and the fruit is edible. However, a severe coating of fungus can block light, thus affecting plant growth. Most importantly, citrus with sooty mold is a sure sign that your citrus tree has been invaded by harmful insects. Read on for tips on controlling citrus sooty mold, along with the insects that create conditions ripe for fungal growth.
Citrus with sooty mold is the result of an infestation of aphids or other types of sap-sucking insects. As the pests dine on the sweet juices, they excrete sticky “honeydew” that attracts the growth of ugly black mold.
Sooty mold fungus can grow wherever the honeydew drips- on sidewalks, lawn furniture, or anything else under the tree.
If you want to get rid of sooty mold on citrus, the first step is to eliminate the honeydew producing insects. While aphids are often guilty, honeydew is also left behind by scale, whiteflies, mealybugs, and various other pests.
Neem oil, horticultural soap, or insecticidal sprays are effective ways of controlling pests, although eradication generally requires more than one application.
It’s also important to keep ants in check. Ants love the sweet honeydew and will actually protect the honeydew producing insects from ladybugs, lacewings, and other beneficial insects, thus ensuring a continual supply of the gooey stuff.
Control ants by placing ant bait under the tree. You can also wrap sticky tape around the trunk to prevent the ants from crawling up into the tree.
Once the pests are controlled, the sooty mold will usually wear away on its own. However, you may be able to speed the process up by spraying the tree with a strong stream of water, or water with a little detergent mixed in. A timely rainfall will do a world of good.
You can improve the appearance of the tree by pruning damaged growth as well.
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My lemon tree is covered in this black sooty like stuff? What is it and how do I get rid of it?
From the image you have supplied it looks like you have a fungus problem known as sooty mould which is caused by scale and/or other sucking insects and is a very common problem on citrus. Carefully inspect your tree, especially the undersides of the leaves, and you will see small scale insects adhered to the leaf. These insects suck the sap out of leaves, producing a sticky sweet substance called honey dew which attracts the growth of sooty mould. This mould can cover much of the leaves, reducing the plants ability to photosynthesise, affecting growth and fruit production.
To treat the problem kill the insects by spraying them with a good quality horticultural oil - good coverage is important, particularly on the undersides of leaves. Once the insects are dead there is no more ‘food’ for sooty mould to grow on so it will begin to disappear. Any fruit that has mould on it is fine to eat simply remove it by washing the lemons with soapy water. Healthy trees are less prone to pests and diseases so regular watering, feeding and attention is important. Citrus are ‘gross feeders’ so apply Daltons Goldcote Fruit & Citrus Tree Fertiliser just outside the branches’ ‘drip line’ at six-weekly intervals from late October to early December, recommencing late February through to early April.
Thankfully, not all pests produce honeydew, so you don’t need to stress each time you see insects land on your plant. Remember, it only shows up on your plant with the presence of this substance.
The insects that produce honeydew include:
It’s crucial to know that both the larvae and adult stages of all of these insects produce honeydew while feeding on your plant.
The first main task in dealing with the mould is to get rid of the insects that are creating the sap secretions.
Use a horticultural pest clean oil such as Neem oil and spray the foliage of the plant to kill off all the insects that have made your plant their new home.
Once all of the insects are removed from the tree you can begin to clean off the sooty mould.
Use a small amount of natural detergent to make a spray and coat all parts of the plant covered in the black mould. Make sure to get both sides of the leaves and let the detergent spray soak the leaves.
You can then either wait for the next good dose of rain to fall to wash the detergent off, or give your tree a good wash down with clean, clear water from the hose and you will see the black soot washing away.
You may need to do this step more than once if the mould cover was heavy. Don’t be tempted to scrub the leave or go overboard on the detergent spray for risk of doing more damage than the mould was in the first place.
If after ‘washing’ your tree you find that any of the branches have sustained too much damage due to the infestation, trim back the parts of the tree that are most affected, making sure to not prune your tree too hard, especially if it is a smaller decorative tree.
Once you have your plant looking more like it’s old, healthy self, make sure you keep on top of the insect control and continue to gently remove any of the sooty mould that remains until you have a display of green, shiny leaves once again.
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Last update on 2021-03-28 / Affiliate links / Images from Amazon Product Advertising API