Common Houseplant Pests
- Make sure to give the plant the proper light and proper water. Overwatering is most often the cause for plant distress, and makes the plant less able to fight off pests and disease. Also, when plants have slower growth or dormant stages, such as winter, they will need less water than during their growing season.
- Fertilizing properly is also helpful. In general, you want to fertilize in the growing months of spring and summer. In fall, and especially winter, either do not fertilize or cut back immensely. There are two general types of plant foods that are applied to the soil---granular and liquid concentrate. The granular types are often slow release, and only need to be applied every few months, according to the package instructions. Liquid concentrates get added to watering cans and fed into the soil that way. Always follow the instructions on the label of plant foods.
- Another type of fertilizing that is often underutilized is foliar feeding. This involves spraying a liquid foliar spray onto the foliage. There are ready to use types, as well as liquid foodsthat mix with water and are applied with sprayers.
- Whenever you buy a plant, or bring it indoors, always check it and its container and soils for pests, as well as signs of pest damage. It is helpful, when a plant is sturdy enough, to use a water spray (such as sink or shower) to wash off dirt and possible insects. It is also good practice to wipe off leaves with a wet cloth regularly.
- Isolate new plants for four to six weeks to ensure that pests do not have a chance to infest the rest of your houseplants. Many insects are difficult to see with the naked eye, or have eggs laid in the soil that will hatch later and infest the plant.
- Pests can enter your home through doors and windows, or on clothing and shoes. Make sure windows have screens, and be careful to avoid transferring pests from one plant to another via your clothing.
- The first step when you discover a plant is infested is to isolate it from your other plants.
- Getting pests under control is not a one-time treatment. It can take a few weeks, depending upon the insect or how bad the infestation.
- Light infestations can often be removed by hand. Or, use a cotton swab dipped in rubbing alcohol to wipe off insects such as aphids and mealybugs. Scale, which create a protective casing, are best scraped off with a fingernail, although sometimes the rubbing alcohol can work as well.
- Spraying with water can remove many pests. However, it is possible that there are eggs that will not be washed away, and will hatch and re-infest. Using an insecticidal soap (or make your own with a few drops of dishwashing liquid in a spray bottle) can also eliminate most pests. You need to completely cover the plant---tops and bottoms of leaves, and stems. This is a contact insecticide----it has to make contact with a live insect to have an effect. For that reason, you will need to repeat this process, possibly daily, for a week or two, or sometimes longer. This process is most effective against soft bodied pests such as mealybugs, aphids, spider mites, thrips and whiteflies. Immature scale, which hasn't created its protective coating yet, can often also be contained with this.
- If a plant is heavily infested and not a very expensive or valuable one, it is sometimes best to simply discard it.
- There are also stronger, chemical insect sprays that can be purchased for indoor plants. Make note that most are designed for outdoor use only, and even the ones labeled for indoor use need to be applied following the instructions on the label---these chemicals can cause harm if breathed in by humans or pets. They also can damage furniture. It is best, if possible, to take the plant outdoors where there is plenty of ventilation to avoid inhaling fumes.
MAJOR HOUSEPLANT PESTS
Aphids: Small, soft bodied insects about 1/16 to 1/8 inch long. Often green, they also might be pink, brown black or yellow. Adults may or may not be winged. Usually aphids are found feeding on new growth and the underside of leaves. They suck sap from the plant, resulting in yellowing and misshapen leaves. They can also stunt growth and cause new buds to be deformed. Aphids also secrete a sticky material called honeydew, which leaves a shiny and sticky area. Sooty mold can grow on the honeydew.
Controlling minor infestations can often be done with spraying or handpicking. Insecticidal soap spray, as discussed above, can be effective but must be done regularly and repeated many times.
Fungus Gnats: Only about 1/8" long and rather delicate looking, fungus gnats are often seen running near or on the soil surface, and flying around near the soil. Although adults do not feed on plants, they are a nuisance and can grow to fly and congregate around windows. The larvae feed on decaying material or fungi in the soil. Some species of larvae can feed on roots, which can cause plant distress, particularly in younger plants. Moist soil is the major culprit in allowing fungus gnats to proliferate.
Controlling fungus gnats is simplest if you can allow the soil to dry out completely (or at least the top two to three inches). In plants that require evenly moist soil this is not a good solution, as it will stress the plant and make it susceptible to other infestation. Make sure to empty saucers of water. There are also products with 'bacillis thuringiensis israelensis' (BTI), which is biological control. Most often used to kill mosquito larvae in standing water, they also work with fungus gnats. Often in granular form, they can be applied to the soil and watered in. Another method is to soak the BTI granules in a watering can for 30 minutes or so, skimming off the granules and then watering the plants. This "BTI Tea" can soak the soil more evenly than allowing the granules to sit on the soil.
Mealybugs: Small, pale insects about 1/8 to 1/4" long. Adult females have a white, waxy covering that give a cottony look. They move slowly, some female species are able to fly, so isolating from other plants is essential. Nymphs hatch from eggs, and then begin to feed, which is when the waxy coating develops. This waxy coating can make controlling them more difficult. Mealybugs also secrete honeydew. In addition to sooty mold, honeydew can attract ants---while this is more of an outdoor problem, it can cause issues indoors as well. Mealybugs are most often found on the undersides of leaves, in the nooks and crannies where leaves attach to stems, and on new growth. They suck sap, which causes stunted growth and possibly killing the plant.
Controlling minor infestations may be controlled by removing by hand or using a cotton swab dipped in rubbing alcohol. Insecticidal soap sprays can work. Again, because eggs are usually present, you will need to repeat these steps daily until the infestation is under control.
Scale: There are several species of scale that fall into two categories--armored and soft.
Armored scale covers itself with a waxy covering that can be scraped off. Soft body scale secretes a waxy coating that is integral to its body. As there are different species, they can vary in appearance. Some appear flat, others look like waxy bumps. Adults are small and do not move, and feed by sucking on the sap of the plant. Immature scale are called crawler and are mobile, also feeding on sap. They are most often found on stems and the undersides of leaves. Like aphids and mealybugs, soft body scale secrete honeydew, whereas armored scale do not.
Controlling early infestations can often be done by scraping off with a fingernail. Adults are well protected with their waxy coating, so insecticidal soaps are generally ineffective on adults. It does work on the immature crawlers. Products with neem oil extractcan suffocate the adult scale, however, neem oil should always be used outdoors.
Spider Mites: Related to spiders, these are extremely small and are very easy to miss. Quite often it is damage to the plant that is what is discovered first. Heavier infestations will have a web. Sucking from spider mites causes speckling on the upper sides of leaves and can cause a plant to look faded. If not controlled, leaves discolor and the plant dies. Houseplants that are indoors year round are the most susceptible, ones that spend the warmer months outdoors tend to have less of a problem.
Controlling mites can be done with a strong spray of water (be careful with delicate plants), especially the undersides of leaves. Insecticidal soap spray can also be effective, but must be done consistently and regularly until the infestation is under control.
Whiteflies: Related to scale, mealybugs and aphids, whiteflies are not actually flies. They are quite small, around 1/16 on an inch long and resemble tiny moths. They cause damage similar to aphids, and also secrete honeydew. If an infested plant is disturbed, they will fly about and then settle back onto the plant after awhile.
Controlling whiteflies is best done with washing the plant and spraying it regularly with insecticidal soap.
Thanks to Clemson University College of Agriculture. For more information visit clemson.edu
Images courtesy of Arbico Organics. For more information visit arbico-organics.com