Mealy Bug on Houseplants

I have worked in Horticulture for the past 36 years specializing in interior tropical plants; houseplants. Over the years, I have worked in many tropical greenhouses, the last being in a retail garden center. With hundreds of plants under my care, I had to maintain a constant diligence in the fight against insects that would colonize in the product. This was no easy task because I was limited on the types of insecticides we could use to combat any developing infestations. As a result, I developed methods to prevent any devastation from happening before serious problems spread. In these articles, I will discuss these methods in the form of guidelines, which I use daily on my plant collection in my home and in all the greenhouses.

Mealy bug is a type of scale insect that penetrates the plant surface with its mouthparts and sucks out vital nutrients important to the health of the plant. The insect is a white small oval that hatches from eggs laid by adults in sacs that resemble puffs of cotton stuck in the nodes (joints) of the stem where the leaf grows from the stem of the plant, as well as on the leaf top and bottom surfaces. The egg sacs swell in moist, humid conditions and when the eggs hatch, the miniature adult crawls over the plant until it finds a suitable area and chows down.

The bodies of these beasts have a covering of a white waxy substance that is impervious to water. This protects the body from sudden rain showers and prevents it from being washed or blown away. As the insect sucks nutrients, it secretes a honey-type substance that may coat a lower leaf and even the floor under the plant. If a plant is heavily infested with mealy, this honeydew may cover leaves over a huge area of the plant.

Mealy is visible by the white cottony blotches in the crevices between leaf and stem and the undersides of the leaves and new growth at the tips. The damage often manifests as frequent leaf drop of the leaves around the sac areas. If left untreated, this infestation will cause massive leaf drop resulting in plant death. The little critters can spread to other plants nearby using various means of travel; blowing off an infested leaf and floating through the air until it reaches another plant, falling into the watering can and then watered into another plant, hitching a ride on a pet's/person's body, or traveling across adjoining plants via touching leaves. The sacs are small enough to come through screens in windows and doors on summer breezes.

I consider a mealy bug infestation to be the hardest of all the houseplant insects to get rid of because the egg sacs do not always settle on live plants. They can adhere to any rough surface, such as the underside of a shelf, and can remain dormant for up to ten years. The egg sacs look like tiny dust specs floating in the air current of your home. They hit a surface and adhere to it until temperature and humidity are right for development. The tiny insects are miniature adults and can crawl to the nearest leaf for its first meal. If many plants have mealy bug, the task for getting rid of them is very difficult.

It a plant has mealy bug, the easiest method of eradication is with an insecticide developed for mealy bug. If the label does not specifically state mealy bug then it may not have any effect on the insect and may do more harm to the plant. The treatment with insecticides is no more frequent than once a week, but one spray application will not get rid of an infestation. The treatment for an infestation, where a plant has multiple egg sacs and individuals crawling throughout the plant, is extremely difficult and time consuming.

Insecticides only work if they hit the individual insect or egg sac. Most of those designed for interior use are not very strong and several applications are needed to combat the infestation. Since recommendation for insecticides are only once a week, the colony can replenish itself in those times between sprays. The battle for the plant needs daily attention. On the days between sprays, the plants need our attention to combat these little monsters. The cottony egg sacs and individuals need attacking on a daily basis if there is to be any hope of getting rid of the mealy completely.

When I notice mealy on one of my plants, I immediately go on the attack with my fingers and wipe all that I see. I rinse any leaf that may have honeydew on it with tepid water and gently rub it until all sign of the sticky is completely gone. I will then use an insecticide, spray all surfaces, top, and bottom to try to get as many insects as possible.

The next day, I will check the plant again, and remove any sign of mealy with my fingers, talking extra care to check the entire plant thoroughly.

Besides using an insecticide on a heavily infestation, I often use isopropyl alcohol, rubbing alcohol, in a spray bottle and spray any egg sac or insect I see, being very careful not to drench new tip growth because the alcohol will burn delicate leaves. Alcohol works on mealy bug buy dissolving the waxy layer and exposing the brown body. The insect soon dies. If used carefully, alcohol will not harm the plant because it evaporates too fast. Alcohol will not kill any of the other type of insects that infect houseplants. I often read how it is a homemade, "organic" remedy to treat bugs on plants but this is not the case. Alcohol is a harsh chemical and can do much harm to the plant if not used carefully, especially if it does not kill the bugs.

Dish detergent is another very harsh chemical and should NEVER take the place of an insecticide. All too often I have seen the results of dish detergent on houseplants. Plant death is often a result. There is no insecticide that is not toxic; they all were designed to kill. The safe part comes with the correct use of them by following the manufacture's directions.

For a heavy infestation, you must spray the plant with an insecticide on day one, and use your fingers and alcohol spray on days two through six, spraying on day seven again with the insecticide. This must be continued until there is no sign of any mealy for two straight weeks, checking every day for any signs. If this is not done daily, I can guarantee you will never get rid of mealy bug in your plant(s). Then a return to the weekly check to make sure no further problems arise.

But this is not the only thing you have to do. This is only treating what is on the plant(s). As I mentioned previously, egg sacs can adhere to any surface and remain dormant for up to ten years. In the case of an infestation, you will need to clean the entire area around the plant(s) and wash any surfaces with warm, soapy water. This will get rid of any dormant egg sacs. So many times customers come to me telling me how they treated their plants daily, but mealy still comes back. And this is why. If you do not clean all the areas around the plants, the shelves, the floor, curtains behind the plants, windowsills, and even the window glass, you are only keeping mealy to a minimum. Once you stop treating your plants, mealy will return again soon. This I know as a fact.

Like the health professionals tell us, the best medicine is prevention and so this is true with plants as well. Their health depends upon you to provide them with the best environment possible by giving them the light level they require and the proper watering schedules. If you check your plants once a week all year long, you will see something that may not be right very quickly. If it is an insect, a quick wipe with the fingers will take care of the problem and prevent any future problems. All infestations begin with one or two individuals and if stopped dead, no further growth will ensue.

However, if you take several weeks or months off, when you check out the plant, you may be in for a rude awakening. Somehow they took a hold and now you are faced with tedious and time-consuming treatments that will stress the plant as much as the insects.

One of the most important preventative guides I can give you is not to put any of your houseplants outside for the summer. If you do, the plant becomes weakened from the change in environment and if insects were nearby, they will take a foothold faster and the plant will not have the vigor to fight them. See the article, "Putting houseplants outside for the summer". This article explains what a plant goes through when it is put outside and then brought back inside and how the changes in the environment affect it.

One evening when I was watching a movie, I noticed a large dust spec float across my face just inches away from my eye. Curious, I watched it move across the room until it came within a few inches away from one of my Anthurium plants sitting on a plant shelf a few feet away from me. As I watched it, the speck did a 90-degree turn and floated on to one of the leaves of the plant. I immediately rose and checked out the plant, never taking my eyes away from the spot where I saw the spec land. Upon close inspection, I noticed that spec as well as two others on the underside of one of the leaves. It was a mealy egg sac and some type of force attracted it to the leaf, where it attached itself and would remain until conditions were good for hatching. I immediately wiped all three sacs off with my fingers and then took the plant to the kitchen for close inspection. Luckily I did not find any other signs of mealy, but checked the plant daily for a week to make sure no further problems arose.

I cannot stress how important it is to do a weekly check on each of your plants all year long. This simple procedure has kept my plants healthy and mostly insect free both in my home and in the greenhouses I manage. (I say mostly because insects are out there and at one time or another they will get into your plants!)

Here is a list of the plant that are most susceptible to Mealy Bug:

Abutilon (Flowering Maple), Achalypha (Chenille Plant), Aeschynanthys (Lipstick Plant, Goldfish Plant), Alamanda, Aglomena (Chinese Evergreen), Anthurium, Amaranthus, Aphelandra (Zebra Plant), Araucaria (Norfolk Island Pine), Ardisia (Coral Berry), Asparagus (all species) Aspisistra (Cast Iron Plant), Azalea,