How to Get Rid of Mealybugs [2022 Updated Article]

What’s that on your bonsai? Is there a patch of white, fluffy-looking insects? Well, you might have a mealybug infestation.

The primary bonsai pest is the female mealybug, which feeds on plant sap. While sucking the plant juices, they attach themselves to plants and produce a powdery layer of wax (also called honeydew). This waxy layer can be home to 50 to 100 eggs depending on the species.

Mealybug infestation.

The main mealybug species that affect bonsai plants are the long-tailed mealybugs (Pseudococcus Longispinus) and the citrus mealybugs (Planococcus citri).

This article will review what mealybugs look like, what they do to bonsai plants, and how to treat them.

The Mealybug Pest

Mealybugs suck the juice of host plants which severely damages the plant. The result is that the leaves become yellow, distorted, or eventually fall. If the infestation is not treated, sooty mold fungus may grow in the excretion.

Control the Issue Before it Happens

Do not allow mealybugs to roam free, as they can quickly take over your home in plague-like proportions. Preventing pest infestations is always better than treating them. Plants that are healthy and vigorous are more resistant to insect attack. So make sure you have healthy soil.

Getting rid of Mealybugs

There are several ways to get rid of mealybugs.

  • It is possible to squash large mealybugs easily with your fingers. To smother little ones, you can use Eco-oil. You can also douse them in methylated spirits to dissolve the mealy coating. This will cause them to dry out and eventually die.
  • Soap recipe: Combine one teaspoon of organic washing-up liquid and three liters of water to make a weak soap solution that can be used to spray on plants.
  • Garlic recipe: Mix one garlic bulb, one onion, and one teaspoon of cayenne pepper. Blend until smooth. Then, add one liter of water to the paste and let it sit for at least an hour. Strain the mixture and add one tablespoon of washing-up liquid. Mix thoroughly and spray onto the mealybugs. The mixture can be kept in the refrigerator for several hours.

Neem oil from the neem tree is recommended. It can be purchased at organic outlets and online.

  • Lady beetles and wasp parasitoids are natural enemies. You can purchase friendly insects from breeders. This is a great solution for those who grow their bonsai outdoors.
Mealybug on the underside of a leaf.

Using Neem Oil on Bonsai

Neem oil is a great preventative and solution for a mealybug infestation. It is derived from the seeds of a tree in the mahogany family.

The oil is organic and acts as a fungicide (controlling sooty mold, black spot, rust, mildew, and scab) and as an insecticide (controlling whitefly, aphid, scale, and mealy bugs).

Neem oil is also a natural insect repellent and can be used on other house plants you have throughout your home. It is also biodegradable!

A disadvantage of neem oil is it can also kill beneficial insects (ladybird nymphs, lacewings, hoverfly larvae, predatory mites, parasitic wasps). But this shouldn’t be an issue if you are controlling mealybugs inside.

When applying neem oil to your bonsai, you must cover all of the plant, especially the underside of the leaves. Neem oil is a contact spray (it has to hit the mealybug to kill them). Where infestations are severe, you may need a follow-up spray two weeks later.

Always spray in the early evening when there is no direct sun and it is cooler.

Some people have found that reducing the concentration of neem oil in the spray from 2% to 1% has reduced the risk of damage to plants, and the oil has been just as effective. However, this is something I have not tried. Always ask for advice and read the label carefully.

Using Insecticidal Soaps on Bonsai

Soft soaps used to control insects like mealybugs as well as other scale insects are called insecticidal soaps. Soft soap is a liquid soap that is easily soluble. It is made with potassium hydroxide rather than the harsher sodium hydroxide. 

Dishwashing liquid is an examples of soft soap.

  • It enters the insect’s mouthparts, disrupting their cell membranes and causing them to leak their contents
  • It may cause the cuticles to become wavy, leading to water loss through evaporation and, eventually dehydration.
  • It could cause suffocation by blocking the insect spiracles
  • It may also interfere with the growth hormones of insects or alter their metabolism.

Pro Tip: Bar soaps (or hard soaps) should be avoided as they contain salt (sodium chloride), and caustic soda(sodium hydroxide), which can damage plants.

Identifying Mealybugs

Sexually, male and female mealybugs have different forms and structures. The females look nymph-like all their lives. They can move and have no wings. However, males are usually short-lived and eventually become nymphs (or winged wasp-like adult). They can’t eat like adults, and they only have one job: to fertilize females.

Mealybug Infestation

Mealybugs can cause yellowing, wilting, and decline in bonsai tree health. This is known as sooty blotch. The “honeydew,” the secretion of mealybugs, is one of the most obvious signs of an infestation. 

This sticky, sweet liquid attracts many ants. Honeydew is a natural defense mechanism for ants to protect their mealybug enemies to survive. It is easy to determine if there are mealybugs-infested ants. This often happens when mealybug infestation happens outside with bonsai.

Mealybug larva is short-legged and can move quickly to search for food. Mealybugs between the larva and adult stages can cause damage to trees.

The eggs will hatch within a few days after the female has laid them. After crawling around, the larva pierces the leaves, branches, or flowers and begins to suck on the sap of the tree or plant.

Trees with severe damage will become weaker and die if left untreated. 

Mealybugs are also adept at hiding themselves. They often hide in young, rolled leaves. 

Mealybug Reproduction

Mealybugs reproduce quickly because they have a high fertility rate. They can produce multiple generations within a year, and over 90% of their eggs would hatch successfully. 

One mealybug can produce as many as 90,000 eggs.

If you observe two generations of the same insect, it is possible to reproduce up to 90,000. Mealybugs can reproduce parthenogenesis in addition to their sexual reproduction.

Mealybugs Spreading

Some mealybugs cannot crawl very far once they attach themselves to bonsai plants. The transmission rate is low because of this. The male adults do not have wings or feet and are unable to fly or crawl. 

The spread of mealybugs is largely dependent on external factors like wind and human activity.

These tiny bugs can only fly when strong winds are present, which makes indoor spreading less-likely. Mealybugs are transmitted mainly by humans. Make sure to clean your clothing and tools between working on a bonsai.

Identifying Root Mealybugs (the Other Mealybug)

Similar in appearance to the familiar above-ground mealy bug, they both leave white waxy secretions in their wake — like small bits of cotton.

Rhizoecus is primarily a warm climate pest. It is very common in Florida and other southern states.

However, it continues to thrive indoors and in greenhouses if shipped in plants.

These creatures are dangerous to your plants and are often ignored as insignificant or misidentified as mycorrhiza. They are neither!

Rhizoecus americanus

If you doubt, the ideal way to identify them is through a microscope or magnifying glass. If it moves, you can bet it is “root mealies,” not mycorrhiza.

On-Going Detection

An important part of taking care of bonsai trees is to observe them regularly. To detect mealybug in a well-established bonsai, gently lift the tree out of its container and look at the sides and bottom of the root mass. Many times you need to search no further.

Although root mealybugs can occur throughout the roots, they are most obvious along the edges. They can also appear on the inside walls of the container and sometimes even underneath the pot.

Also, while pulling weeds, observe any soil that may come up with the weed roots. Infestations can develop from containers onto old wooden nursery benches.

Root Mealy Bugs Control

Spraying common chemicals or even repotting is often insufficient to eliminate root mealy bugs.

The Answer: Bioadvanced: 12-Month Tree and Shrub Protect and Feed Insect Killer and Fertilizer.

You may find this valuable product a little pricey if you only have one or two plants.  Consider sharing the container with a friend.

A Non-Chemical Option

Before I included this information, I researched the online mention of this technique conducted by the University of Hawaii College of Tropical Agriculture. 

Their research found that “hot water dips alone kill root mealys.” I contacted Dr. Arnold Hara (the professor in entomology who wrote the article) for more details.

About water temperature, Dr. Hara responded, “A meat thermometer should work.  Water at 120 F (49C)  for 6 to 10 minutes is sufficient to control most insects.”

That sounded good news, so I asked about potential damage.

There may be some damage, but it should grow out of it; I recommend doing a test on a few plants before treating mass numbers. Some may be sensitive.”

Dr. Hara of University of Hawaii College of Tropical Agriculture

After this discussion, I would consider “hot water” for stock plants. (I would not personally use the process for bonsai.)  However, give it a try if you are in a “do-or-die” situation from this pest.

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