Check your houseplants for pests
BROOKINGS – Do you talk to your plants? Don’t be embarrassed if you do, says David Graper, Extension Horticulture Specialist and Director of McCrory Gardens.
“They can be very good listeners. They never interrupt,” Graper said. “However, talking to your plants can be beneficial because it gets you up close to your plants where you might notice that the plant has a pest problem.”
Graper points out that houseplants are susceptible to a variety of pests including one of the most common, the spider mite.
“Spider mites are actually an arachnid, like spiders, and have eight legs, just like a spider. Two-spotted mites actually make tiny webs too, which are often noticed before the mites which are almost too small to see with the unaided eye,” he said.
It is important to check your plants for mites, particularly during the winter months when homes are heated and the humidity becomes very low, which Graper says is just what mites like.
“Because the mites are so small, they can spread around in a home just by the typical air currents that are found in a home,” he said. “They can also hitch a ride on you as you move from one plant to another. Spider mites can reproduce in just a few days in a warm location, so populations can explode in a few weeks.”
Spider mites feed by sucking sap from individual plant cells. Plant cells soon turn yellow or brown when they are fed upon causing the plant to develop a speckled appearance on the leaves as you have dying cells next to healthier green cells. Graper says learning how to identify this type of damage is probably the best way to notice a mite infestation because you can see it from several feet away.
Mites like to feed on the undersides of leaves at first but will feed on all parts of the plant in a heavy infestation. To check your plants for mites, use a hand lens or magnifying glass to have a better chance at seeing the mites. Another way to check is to briskly tap a leaf or small branch over a dark piece of paper. Then look for the tiny speck-like mites that will be moving slowly across the paper. A similar method involves using a white piece of paper in combination with the smear test. After you tap the leaf over the paper, rub your finger over the paper to crush and smear the remains of the mites on the paper. If you have mites, you should be able to see brownish streaks where ever you mushed some mites – a little gross but effective.
Treating spider mites
There are a number of treatment options for spider mites. First, Graper says, you should assess how bad the infestation is.
“If you can see that most of the plant is encased in webs and they are crawling with mites, the best treatment is probably to carefully place the plant in a bag and get it out of the house,” he said. “Setting it outside when it is about 10 F outside is a pretty effective treatment for killing the mites.”
With this treatment you’ll also need a new houseplant, Graper jokes. “But the old one was beyond help.”
He adds that once you dispose of the plant, change all clothing that may have come in contact with the plant and wash it. “Then go and check the rest of your houseplants, starting with the ones closest to the infested plant you just discarded,” he said.
If you catch other infestations before they have overrun the whole plant, Graper says you can prune off badly infested leaves or branches.
“Also, a forceful jet of water will blast away lots of mites,” he said.
To do this, put the plant in your kitchen sink or shower and spray it down. The jet of water will also destroy the webs and have a better chance of reaching more of the mites. Use tepid water and try to get the water directed to all parts of the plant.
Another option, for larger plants, is to moisten a soft cloth or small sponge and use that to wipe down the leaves and stems. Adding a little dish soap to the water will help do a better job than just plain water. Graper says you can also mix up a spray bottle with a few drops of dish soap and a tsp. of vegetable oil, and then fill the bottle with water. Shake well then spray it on the plants. You might want to try this on a few leaves first to make sure you don’t damage the plant’s leaves. If you don’t see any damage after a few days, then it is probably safe to use.
Graper adds that there are also commercially available products that can be even more effective in killing mites. Insecticidal soap and horticultural oils can work well.
“The nice thing about these products is that they are very safe so they can be used inside the home. But read the label carefully and follow the directions,” he said.
There are other miticides available in your local garden center or hardware store, but again, Graper reminds homeowners to read the label to make sure it says it will control mites and that it can be used on houseplants or ornamental plants.
“You may want to move the plant out to a heated garage to treat them. Wait until they dry then bring them back into the house,” he said.
Whichever treatment you use, Graper says you will likely have to retreat every five to seven days or so to kill the new babies that have hatched from the adults you missed with the last treatment.
Mealybugs are another common houseplant pest.
“These insects are much larger than the mites and are usually covered in tiny filaments of white wax making them look like little tufts of cotton,” Graper said.
They are often found on the newer leaves of plants and in the cracks and crevices around the stem, leaves or flowers. They will often feed right along the mid-rib on the underside of leaves on larger plants. Like the spider mites, these insects feed by sucking sap from the plant. They can also reproduce quickly and can easily walk from one part of the plant to another or from one plant to another. Typically though, you will see them just sitting on the plant, barely moving.
Another good sign of mealybugs is the presence of honeydew. Graper explains that this is the sticky waste products that mealybugs produce. It will look like shiny spots or areas on the plant’s leaves or on your windowsill, beneath the plant. Other members of their group of insects, such as aphids and scale will also produce honeydew.
“Many times people will notice the honeydew and then realize that the plant that is growing above it is infested with one of these pests,” he said.
Mealybugs can be controlled using many of the same techniques used in treating mites. But, the classic treatment is to use a cotton swab dipped in rubbing alcohol and dab or wipe the mealybugs off the plant. The alcohol is able to dissolve the waxy, protective coating from the insects and then causes their bodies to dry out and die. You can also moisten a small soft cloth or sponge with the rubbing alcohol and wipe the leaves with that. Some people will just spray the alcohol on the plant’s leaves or add it to the mix of dish soap and vegetable oil recipe I mentioned earlier, using one to two cups of alcohol instead of some of the water in a quart spray bottle. But I advise that you test this on a few leaves to see if the plant is sensitive to this mix. You could do as much damage as the insects.
Scale is the last major pest Graper discusses. There are many different types of scale insects but the most common one you may find on your houseplants is the soft brown scale. Scale insects are small, flattened insects that may go unnoticed at first and may not be observed until you notice all the sticky honeydew on the leaves or on the areas around and under your plant. The adult scale insects are about 1/8″ in diameter and are usually brown in color. They reproduce by eggs, which can often be seen if you flip one of the adults over on its back to reveal the tan to brown eggs underneath. Once the eggs hatch, the baby scale or crawlers, move around on the plant looking for a new place to hunker down and start feeding. Once they start feeding they generally don’t move around at all, just stay there and suck plant sap and produce babies.
Controlling scale can be quite difficult, Graper says.
“The adults have a thick waxy covering on their body that resists many kinds of insecticides. The crawler stage of the insect is actually a lot easier to kill,” he said.
The soapy sponge or cloth might work better than just spraying it onto the plants, Graper suggests. Some people will use an old soft toothbrush to gently dislodge the adult scale insects from the plant. But again, like the mealybugs it is almost impossible to get rid of all the scale. Scale will feed on just about any kind of houseplant but they prefer those with smooth or waxy leaves and stems.
“Honestly, because these can become such a serious pest problem, I would suggest at least isolating an infested plant from the rest of your healthy plants or better yet, get rid of it,” Graper said.
To learn more, visit iGrow.org.