Although I feel no affection for this topic, many gardeners (myself included) struggle with scale, spider mites, whitefly, and aphids outdoors in the summer season and indoors in the winter. I thought some basic information, emphasis on basic, on these insect pests would be welcome.
The many species of scale which feed on all types of plants is categorized into two groups: armored (hard) and soft. Females lay eggs beneath their bodies which usually hatch within a one- to three-week period. The newly hatched pin tip sized crawlers are mobile and move to other fresh areas on the plant for feeding.
When the hard-bodied type females select a spot and insert their mouth parts into the plant to suck on the sap, they are no longer mobile and gradually build up a hard outer shell which is often undetected and difficult to treat. Adult males have wings and they look like small gnats. On indoor plants, there may be several generations per year. Their presence is often first detected by the shiny dots of honeydew they excrete, followed by damage to the host plant which manifests in yellowing leaves. Look for them on the undersides of leaves or along the branches. If left untreated, they can severely weaken the plant, sometimes to the point of death. As there are many types of scale, keep an eye outside too because they can be a serious problem in the garden on trees and shrubs.
Mealybugs are a soft-bodied member of the scale family. They produce multiple overlapping generations of fluffy white insects which often prefer softer tender growth and can be controlled with the same methods used for the other pests in this article.
Spider mites are not true insects but are classed as arachnids, which are eight-legged animals such as ticks, scorpions, and spiders. Spider mites are tiny and are usually detected by their tiny webbing and the yellowing leaves of their host plants. They are extremely prolific indoors and out and should not be ignored if they are spotted. Since they prefer hot dry conditions and the accompanying dust, the humidity of a water hose or a mister is highly recommended.
Whitefly, another sucking insect, have developed some resistance to many synthetic pesticides. Whitefly adults look like tiny white moths and can rise in clouds when disturbed. They also have a crawler nymph stage, during which they are almost invisible. The full whitefly life cycle is only 25 days and as their population grows, they cause yellowing, desiccation, and leaf curl on the host plant. They can also spread several plant viruses and generally weaken the health of their hosts. As with many other sucking insects, they deposit sugary honeydew which attract ants and can host black sooty mold. Yellow sticky traps made for whitefly are helpful for monitoring and can mildly suppress the adults.
Aphids are small soft-bodied insects that may be green, red, grey or even black depending on their food source and species. They are usually but not always, wingless. Instead of laying eggs, they have live birth and prolifically breed many generations per year. They deposit copious amounts of honeydew and are sometimes guarded by ants who harvest the sugary honeydew. You may also notice leaf curl or yellowing leaves, stunting (think snowball bush or your favorite plum tree in the spring), and general lack of vigor in their host plants. Some types of aphids attack the roots of plants. Along with other types of insects, aphids can also cause plant gall and other deformities. Once you have the pest under control, the damage should not continue. However, the already-damaged leaves will not fully recover. Aphids are attracted to plants with high nitrogen levels and fresh tender leaves, so don’t over-fertilize and keep a sharp eye on new growth in the spring.
Fungus gnats are another pest that can thrive on winter houseplants. Unlike most pests, they damage plant roots and require a different treatment to get rid of them. Preferring to lay their eggs in soft moist soil, the best defense is to let the top two inches of soil get dry between watering. A layer of sand on top of the soil also makes for an inhospitable nursery. Yellow sticky traps can help put a dent in the adult populations.
The following practical controls for scale, spider mites, whitefly, and aphids can be used outdoors and indoors:
Nature has her own methods for staying in balance, so aim for good health and the least intervention necessary. Natural predators to these pests include parasitic wasps, lady bugs, lace wings, other insects, and even birds. Healthy plants are often able to repel or at least ride out insect pest infestations. For this reason, water your plants regularly and feed as they require it.
I always begin my battles with water. Often a good spray with the hose (or the shower) is very effective and a safe opening salvo. Remove badly infested areas of the plants and remove as many of the remaining insects as you can by squishing them and then washing them off again. A quality mister is a good friend for indoor plants, especially if spider mites are a problem.
Take a few minutes to water the roots of plants that may be new or young or in un-sheltered parts of the yard that receive a lot of sun and drying wind. If there is no snow cover, it could mean the difference between survival and death, especially if the plants have been weakened by harsh weather and untreated pests.
If an indoor plant is small enough for you to reach all of it, it is often effective to remove the visible pests by hand and wipe the leaves and stems firmly with a damp rag or a makeup sponge soaked with alcohol. Or simply squish the pests one by one while wearing an evil grin, then rinse if possible, and continue with stronger treatments only if necessary. It is best to prune out densely infested areas and immediately dispose of them.
To combat pests during the outdoor growing season, it is always best to start without chemicals to avoid damaging the many beneficial insects which will be attracted to your pests. Sometimes you can even purchase those beneficial insects.
If you had trouble with scale, spider mites, or aphids this past summer outdoors in your garden, a good next step this winter would be to spray your plants with horticultural oil in late winter or early spring before bud break, being careful to cover all stalks and stems. Horticultural oil works by smothering the overwintering insects and eggs. It is safe to use on most outdoor and many indoor plants but you must cover the whole plant surface whether indoors or out.
The use of insecticide should be carefully considered, and the safest products tried first. There are some new organic insecticides on the market containing citrus oil which are very safe. The next line of defense which can be used indoors or out is an insecticidal soap such as Safer Soap. After removing what insects you can, a dose of insecticidal soap followed by a light treatment of horticultural oil is helpful. The soap is more effective on the crawler stages of scale while the oil which smothers the pests is effective on all stages.
The chemical azadirachtin which is derived from neem oil is potent on insects including scale, spider mites, white fly, and aphids, if absolutely necessary. A botanical pesticide, it is safe for organic production and can be applied up until the time of harvest if used on food products. It leaves no residue, can be used on indoor or outdoor plants, and is safe for bees.
If you feel the need to use chemicals to eradicate scales in your trees or shrubs outdoors, make sure you research the right time of the season in which to do it, and cover all the surfaces of the plant, keeping in mind that pesticides are most effective on the crawler stage of scale. The Morton Arboretum has a helpful schedule for treatment (http://www. mortonarb.org/trees-plants/tree-and-plant-advice/help-pests).
Always be observant, vigilant, and read and follow directions of any chemicals if you must use them. Even organic, botanical pesticides can be harmful if not used correctly. As Master Gardeners, we have been taught the principles of Integrated Pest Management, so it is a good idea to review them annually and follow them as closely as possible.
Feel free to contact me or any Master Gardener with questions we might be able to answer. Please continue to tap into the vast source of knowledge that we, Master Gardeners, have and love to share. Here’s to another happy, healthy, and productive year in your gardens!
Written and Submitted by Ann McKean