Black Scale Bug on Lemon Trees


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Ever wondered why your lemon tree was dropping leaves with its branches dying and its fruits getting deformed? The possible cause could be citrus scale pests. The most common of them all is the black scale bugs.

The Black scale bug, Saissetia oleae, is a tiny soft scale bug that is native to the southernmost regions in Africa. However, they are now widespread across North and South America, Southern Europe, Australia, Asia, and New Zealand.

Therefore, in this article, I’ll be explaining in detail what they are, how you could identify them, and the best management practices for them.

Everything to know about Citrus Scale Pests

black scale bug on lemon trees

As the name implies, they are small scaly pests that love citrus trees. Their armors are made of was coatings. They are one of the sucking insects that feed on the sap of citrus plants and excrete honeydew that ants love which often results in the cultivation of the black sooty mold, a fungal growth affecting many citrus trees. There are mainly two groups of these bugs that you could find on lemon, oranges, and any other citrus tree. They are the armored scale and soft scale bugs.

Armored scale bugs are highly specialized bugs. Their females are wingless, legless, and eyeless. They prefer to feed on a spot throughout their lives. Once they’ve inserted their mouthparts into the plant, they never leave that spot and that’s where they’ll reproduce. Their male species do not feed during their adult stages and they remain immobile till they mature fully. Talk about having a highly unusual lifecycle. Also, their armored scale which they leave behind when they die remains of various parts of the fruit.

Soft scale bugs also have a protective coating that is made of wax but it isn’t quite as hard as that of the armored scale bugs. Also, unlike the armored scale bugs, their scales cannot be separated from their bodies. The females roam the barks of trees till they begin to lay eggs.

These insects are now considered to be threats to agriculture because they stunt growth, deform fruits, and eventually kill them by creating room for contamination by other pests and fungal diseases.

Good to Read : How to Grow Citrus Fruits?

Signs, Symptoms, and Problems Caused by Black Scale Bugs

  • Black Sooty Mold: The presence of black sooty mold is an obvious sign that sap-sucking insects like black scale bugs are feeding on the plant. When black scale bugs feed on sap, they excrete honeydew. Honeydew is a sweet and sticky substance. Both the exposed sap from the wounds and the honeydew attract and help breed the sooty mold fungal thread.
  • Leaf Chlorosis: When leaf chlorosis occurs, it is a tell-tale sign that the plant is nutrient deficient. Leaf chlorosis is a condition whereby the leaves of the lemon tree begin to turn yellow due to the lack of chlorophyll. Because sooty mold covers the surfaces of the plant, it is difficult for the leaves to capture enough sunlight for photosynthesis to occur. Since photosynthesis doesn’t occur, there’ll be no production of chlorophyll.
  • Branch Dieback: This term refers to the steady death of the branches and shoots of lemon trees due to nutrient deficiency. You’ll notice the affected parts beginning to thin. If this occurs for a long period the tree will eventually die.
  • Reduced Fruit Formation: Since sunlight and fruit formation go hand in hand for all plants, their abundance and development will be largely affected.
  • Premature Leaf Drop: Because of the lack of sunlight due to the attracted sooty mold, the lemon plant will be unable to shoot upwards towards the sun’s direction. This reduces flower formation and the massive shedding of leaves.
  • Presence of Ant Colonies: Ants feed on the honeydew produced from black scale bugs. They protect the bugs and feed on them. Having these colonies dwell in your plant will only deplete its nutrients sooner.
  • Plant Death: If the situation is not contained and the nutrient deficiencies occur, the lemon tree will eventually die.

Management Practices for Black Scale Bugs

The best control method to adopt is any that curbs the number of insects that dwell on the lemon tree.

Insecticide Application: The direct application of an insecticide is a chemical control method for managing scaly bugs. A botanical type such as an organically approved petroleum spray or any having pyrethrin as an active ingredient will do.

A good recommendation is PyGanic Gardening’s Botanical Insecticide that kills the bugs once they come in contact with it. If they eat it, their nervous systems will become paralyzed thereby causing them to die.

If you’re looking for a homemade insecticide that is non-toxic and wouldn’t be of harm to your pets and kids when playing in the garden, the following DIY mixtures will help:

  • Insecticidal Soal and Oil combination: Mix 1 cup of neem oil, a teaspoon of insecticidal soap, and two cups of water in a spray bottle. Apply this to the insects.
  • Oils and Spices combination: Mix 1 cup of vegetable oil with a gallon of water and a tablespoon of cinnamon oil. You can add a dash of chili powder to this mixture. The bugs can’t stand their taste. Hence, they’ll keep off your lemon plant and for those already on the plant they’ll get suffocated and die.

Ant Control: Since the symbiotic ecosystem caused by the black scale bugs and ants causes a nutrient deficiency in your lemon plant, you can get rid of the ants by introducing their greatest natural enemy. Parasitoid wasps and scale bugs are enemies. By introducing them to your tree, they’ll kill off all the bugs which indirectly chases the ants away because they’ll have nothing to feed on.

Black scaly bugs are quite difficult to get rid of. Therefore, prevention is the best cure. Ensure that you buy certified nursery stock to prevent the additional expenses that will be incurred in managing the sap-sucking insects.

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