How to Get Rid of Scale on Plants

Controlling Scale on Outdoor Plants

Scale insects in the garden can be combated in several ways, the best of which involves prevention or removing infested plant material before the insects can spread. While you may not need to take all of these steps, you may need to employ a combination to defeat a scale bug infestation.

1. Prune

   Pruning infected branches is often the easiest and surest solution if you catch the infestation while it is still light. Inspect the plant thoroughly and any adjacent plants to ensure you have removed all infested stems. Do not compost infected plant material; it is best to bag it up and throw it in the trash or burn it safely.
   

2. Treat With Rubbing Alcohol

   Rubbing alcohol can kill scale insects if the infestations are light. The best approach is to put the rubbing alcohol directly on the scale bugs using a cotton swab. However, this can be pretty laborious in an outdoor garden, so you can also fill a garden sprayer or spray bottle with a mix containing one part rubbing alcohol to seven parts water.

   Repeat every two to three days until the problem insects are eradicated.
   

3. Spray With Horticultural Oil

   What Is Horticultural Oil?

   Most horticultural oils are some kind of petroleum-based mineral oil, although some vegetable oils also fight pests, such as cottonseed oil and soybean oil. The oil is usually emulsified to make it easier to spray.

   Spraying your plants with horticultural oil is effective in late spring, just before the leaves unfurl. Scale insects can overwinter as nymphs or eggs tucked away in tree bark.

   Spray your plants at this point using a hose-end or garden sprayer filled with 2 to 5 ounces of oil per gallon of water. This application will smother the scale before the insects form their protective coating.

   It's essential to treat the entire plant, as scale can be present on stems, the undersides of leaves, and along the base of the plant. The oil coats the scale insects and clogs their breathing pores, suffocating them.
   

   Tip

   A hose-end sprayer is the preferred application method for horticultural oils as it will make the oil last longer and cover a greater distance.

4. Apply Insecticidal Soap

   Insecticidal soaps can be used to kill scale at the larval stage, but they are not very effective once the insects are anchored and fed under their protective shells. Apply with a spray bottle or garden sprayer until all the leaves are dripping.

   A mix of 1 ounce of soap to a gallon of water is generally a good rule, but follow the package directions to be sure.

   Several applications will be necessary to catch all the larvae because these soaps don't last long in the elements, but these organic pesticides will not leave a dangerous environmental residue.
   

   Warning

   Only apply insecticidal soaps to well-hydrated plants, or you can risk damaging them. Also, never use the product when the plants are in direct sun or above 90 degrees Fahrenheit.

5. Apply Neem Oil

   Neem oil, or any pesticides containing azadirachtin, a key ingredient in neem oil, offers excellent protection against scale and kills the established insects—not just the larva.

   Because neem oil won't mix easily with water, you'll want to add a bit of dish detergent as an emulsifier. A general guide is to use 1 to 2 teaspoons of detergent and 1 to 2 tablespoons of oil to a gallon of water. Apply with a garden sprayer.

   Neem oil and other azadirachtin treatments are considered organic pesticides and are not toxic to honey bees and most other beneficial insects. Other plant-based pesticides can also be successful.
   

6. Use Beneficial Insects

   Beneficial insects such as soldier beetles, lady beetles, and parasitic wasps can be important and effective control for scale insects. You can encourage these natural predators by providing them with food and shelter. You can also purchase beneficial insects by mail to release in your garden.

Controlling Scale on Indoor Plants

Since no natural predators are indoors, scale insects will spread even faster than outdoors. You must diligently control or remove scale when it infests indoor plants. 

If you catch the problem early enough, pruning out the infested stems could alleviate the problems. Keep a close eye on the plant for several weeks to ensure no new scale appears. Dispose of the pruned stems immediately.

Remove existing scale on houseplants by rubbing gently with a facial-quality sponge or cotton swab dipped in rubbing alcohol. The alcohol alone should kill the scale, but the dead insects will remain on your plants, making it difficult for you to scout for new infestations. The small facial sponges in the cosmetic aisle are abrasive yet soft enough to use without scraping the plant stems. Be sure to buy plain sponges without cleanser or lotion in them. As always, test on a small area first since some plants are more sensitive than others.