Posts Tagged ‘controlling mealybugs’

Mealybugs on the underside of a basil leaf

I just noticed that the leaves of my Schefflera are sticky and so is the floor under the plant. What is going on?”

“Some of the leaves on my jade plant are covered with a black sooty film and the table it is sitting on is becoming sticky. Help!”

We get questions like these all the time – especially in the winter when many gardeners turn to indoor plants to satisfy their gardening itch. There are so many types of beautiful houseplants but they come with their own set of horticultural issues just like the outdoor plants do. Sometimes it’s environmental – low humidity causing brown edges or not enough light; sometimes it’s a watering issue – too much water or not enough; and sometimes it’s insect or disease problems.

Yellow stippling on leaves indicates damage from a sucking insect - in this case scale.

Yellow stippling on leaves indicates
damage from a sucking insect – in this
case Euonymus scale.

Sticky leaves, sooty mold, and discolored or misshapen foliage are all signs that some type of piercing and sucking insect like aphids, mealybugs, or scale is present on the plant. These insects have specialized, tubular mouth parts that penetrate the plant tissue and suck out the juices. Definitely not healthy for the plants! As they feed, they excrete a sugary liquid called honeydew that drips onto the foliage causing it to become sticky. Sometimes, with a heavier infestation, the honeydew can drip onto the ground under the plant. This happened to us once with a large Schefflera that was in our sunroom. When I walked near the plant, I discovered that the tile floor was very tacky. It turns out that the plant was infested with scale insects.

Mealybugs on the underside of a basil leaf.

Mealybugs on the underside of a leaf.

Mealybugs which are closely related to scale insects are one of the more common houseplant pests. These are slow-moving, soft-bodied insects that attack a wide variety of plants both indoors and out. They have flattened oval bodies that are usually covered with a waxy coating which gives them a white or grayish appearance. They look a little like the pillbugs (roly polies) that you find outdoors under logs except that they don’t roll up into a ball when you disturb them. Like most piercing, sucking insects, mealybugs are usually found on the underside of the leaves or on the stems of plants.

Sooty mold on laurel - Joseph O'Brien, USDA Forest Service, Bugwood.org

Sooty mold on California laurel

Their feeding can cause yellowing of the foliage, premature leaf drop, stunted growth, and if not controlled could eventually lead to the death of the plant. In addition, the honeydew they secrete provides the perfect growing medium for sooty mold, a black fungus that can spread over the leaves. A heavy coating of sooty mold can inhibit photosynthesis and further weaken the plant.

Female mealybugs lay large numbers of eggs which are often encased in a loose, waxy egg sac that resembles a cotton ball.

Adult mealybug and cottony egg case.

Adult female mealybug and egg case.

These egg cases are usually found on the stems and on the underside of leaves. When they first hatch, young mealybug nymphs (crawlers) move around actively and are likely to move from plant to plant. The adult females, while still mobile, are not nearly as active as the early nymphal stages.

Adult male mealybugs do not feed at all. Their sole purpose is to mate with the females and they survive only a day or two.

Mealybugs and cottony egg masses are easily seen on the underside of a leaf

Mealybugs and cottony egg masses are
easily seen on the underside of a leaf

Mealybugs and many other houseplant pests are sometimes inadvertently brought into the home when an infested plant is purchased. Because of this, it is very important to examine houseplants carefully for any sign of insect activity before you buy them. Look under the leaves and along the stem. Many insects, especially scale, are difficult to see because they really blend in with the plant. Mealybugs will hide in cracks and crevices along the stem and foliage but most of the time they are fairly visible upon inspection.

In spite of their soft-bodied appearance, mealybugs can be surprisingly hard to control because of their protective waxy covering and also their tendency to hide in places that are hard to reach with a spray.  If you find mealybugs on your houseplants, there are several products that you can try.

If there are just a few mealybugs on your houseplant, you can dab each one with a cotton swab soaked in rubbing alcohol. This will kill them right away. Be sure to keep checking on a daily basis for ones you may have missed.

If you have a heavier infestation, horticultural oil such as Bonide All Seasons Oil or PureSpray Green or an insecticidal soap will help control them if you can coat the insects with the spray. These products will also help control other houseplant pests such as scale, aphids, and whitefly. It is important to spray the underside of all the leaves.

Another good choice is Bayer Advanced 2-In-1 Insect Control plus Fertilizer Plant Spikes. These plant spikes contain a systemic insecticide that is taken up by the roots and transported to the stems and leaves. When insects feed on the plants, they ingest the pesticide and are killed. These plant spikes can only be used for ornamental houseplants – never on edibles.

Always read and follow the label directions when using any pesticides!

Enjoy your houseplants this winter! Here are more tips to keep them healthy!

Until next time – Happy Gardening!

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