Winter and Beyond: Scale, Spider Mites, Whitefly, and Aphids

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 janfebmar 11.1janfebmar 10.3groups: 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.

janfebmar-11.5-e1559335804474.pngMealybugs 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 janfebmar 11.6plants. 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 janfebmar 11.2nymph 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. janfebmar 11.3Instead 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 honeyjanfebmar 11.4dew. 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 janfebmar 11.8very 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.janfebmar 11.9

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.

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!

USEFUL LINKS houseplant-pests html?id=17791

Written and Submitted by Ann McKean


Winter Indoor Plant Care

Winter Indoor Plant Care
by Elizabeth Waddington

Here are a few tips to keep your indoor plants thriving through our long cold Montana winters.


  • Pests can be a real annoyance. They usually appear after outdoor plants are brought inside for the winter, or when a new houseplant is brought home. Your houseplants may also sprout bugs once brought inside your house because they no longer have outdoor predators.
  • Spider mites thrive in warm, dry houses. Frequent misting under the leaves of houseplants will discourage them. A solution of 1 cup flour, ¼ cup buttermilk, and a gallon of cool water, applied in a mist, may be a good organic deterrent.
  • Small flies may occasionally appear around houseplants. These are called fungus gnats and are harmless to plants and humans in their adult form, though their larvae can damage young roots. Letting the soil dry out a bit between watering can discourage fungus gnats.
  • Remove aphids from houseplants with a mixture of equal parts rubbing alcohol and water and add a drop of dish-washing detergent. Apply with a soft brush. This also works on mealybugs and scale.

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  • When arranging houseplants in your home, consider their lighting needs. Some plants require lots of direct light to thrive, while others prefer lower levels of indirect light.
  • Put plants that can tolerate full sun in south-and west-facing windows, plants that like partial shade in east-facing windows, and low-light plants in north-facing windows.
  • Most flowering plants need to be within three feet of a sunny window.
  • Most plants require 12 to 16 hours of light per day.
  • Rotate plants once in a while to encourage even growth and prevent legginess.


  • Believe it or not, more houseplants die from over-watering than from anything else! Water plants with room-temperature water.
  • Use filtered water if your tap water contains high amounts of minerals or chemicals. Fluoride can cause the leaf tips of some houseplants such as peace lilies, to turn brown.
  • Water houseplants in un-glazed clay pots more frequently because the porous clay will absorb and evaporate some of the water.
  • If your houseplant leaves are dripping, even when you haven’t watered, it’s trying to rid itself of excess water (a process called “guttation”). This makes a plant vulnerable to disease-causing fungi, so you may want to reduce the amount of water you’re giving the plant.


  • Most houseplants are in a resting phase during the winter and do not require fertilizer. However, a balanced fertilizer (10-10-10) works fine, fertilizers with a higher ratio of nitrogen will promote more foliage growth, and flowering plants can use a fertilizer with more phosphorous.

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  • Most houseplants grow well with daytime temperatures of 65 to 75 degrees F and night temperatures of 60 to 65 degrees F. Temperatures below 50 degrees F or rapid temperature fluctuations may damage some plants.
  • Keep houseplants away from cold drafts, radiators, and hot air vents. Also make sure houseplant foliage doesn’t touch cold windows by placing a cardboard between the window and plant.


  • Humidity is a tough factor to perfect, as most homes are especially dry in Montana winters. Most common houseplants will be happiest when the relative humidity is between 40 and 50%.
  • Group houseplants near each other to form a support group to cope with the low humidity of most winter homes.
  • Set plants on shallow trays of moistened gravel to raise humidity. This keeps the pots out of standing water.
  • Occasionally turning on a humidifier near your plants can be effective at combating indoor dryness. You would have to hand mist plants several times a day to raise the humidity sufficiently.
  • Plants like cacti and succulents can tolerate lower levels of humidity.


  • Loosen the dirt in your pots periodically. Re-invigorate your houseplants by removing the top ¼ inch of soil and top-dressing with fresh potting soil.
  • If your houseplants’ leaves grow dusty, gently wipe them down with a wet paper towel. Too much dust can clog a plant’s stomata (pores), making it harder for the plant to “breathe.”

Challenge: does someone want to try this off-beat tip? To get rid of bugs in houseplants, push a clove of garlic into the plant’s soil. If the garlic sprouts and grows, just cut it back.


Submitted by Elizabeth Waddington


The summer that I turned ten there was a huge spider in our garden. She would spin a new web almost every day. Many days, I would take her off her web and set her on a length of sewing thread about a yard long. She would crawl up the thread until she reached the top, at which point I would spin my arms so she was at the bottom again, and up she would crawl. When we had both had enough, I would restore her to her web and give her a cricket from my ‘cricket farm.’ which was just some crickets in my garden who also served as playmates for an only child in a rural place. She and I played this game until the end of summer when I had to go back to school. I don’t know if the free meal was sufficient compensation for my daily molestation, but she tolerated me and I adored her. I guess it must not have been too awful for her because she stayed there all summer instead of moving her digs somewhere else. It wasn’t until adulthood that I finally identified her as an Argiope aurantia. She was large with yellow and black markings that were reminiscent of a tiger swallowtail butterfly, and her large orb web had a giant zig zag down the center. (Spoiler alert: I love animals, especially insects.)

Spiders, known as arachnids, seem to be right up there with snakes for triggering fear and disgust. The image of the black widow has been woven into our culture as a representation of evil. I would like to convince you otherwise.

My Argiope, common name Yellow Garden Spider, is a fascinating creature. Arachnids are easily identified by their eight legs and – if you get close enough to see – four eyes. As with most spiders, the female is considerably larger than the male. The males wander until they locate a female and then make a web nearby, eventually mating. After mating, the female will make several egg sacs and hang them in her web. The eggs will hatch in autumn, perhaps even after she has died from the cold, but the baby spiders will remain dormant inside the egg sac until spring. Each egg sac contains anywhere from 300 to 1400 eggs. As with other spiders, once a female finds a suitable location for her web, she will remain there all season unless she is disturbed. I suppose my Argiope friend thought the free crickets were worth the trouble.

Black Widow Spider                                                 2018 newsletter 1.1

These beautiful orb webs trap all kinds of goodies including everything from aphids to wasps to caterpillars to grasshoppers, but there are other types of webs that are equally effective, including funnel webs, sheet webs, mesh webs and the good old fashioned tangle webs also known as cobwebs. These webs can be useful in identifying the spiders who made them. I found a black widow in my garden last summer who had wrapped up a bumble bee and a wasp in her tangle web. Spider silk is one of the strongest natural materials, and is being studied by scientists and mechanical engineers for its potential uses.

Spiders are carnivores and are excellent pest control, and even help prevent the spread of disease by eating the insects that can spread it, such as fleas, cockroaches, flies and mosquitoes. Norman Platnick of New York’s American Museum of Natural History says, “Spiders are primary controllers of insects…without spiders, all of our crops would be consumed by those pests.” He postulates that “if spiders disappeared, we would face famine.” Less dramatically, spiders in your house make excellent pest control, and if you can overcome your fear, they can keep your home virtually pest free without chemicals! If the thought of sharing your home with spiders is too much for you, try to capture them and toss them out the door instead of squishing them. They are wonderful partners in your garden for managing all the hungry pests who want to eat your plants.

Although a spider bite is deadly for its prey, most spider bites are little more than bothersome to humans. Furthermore, spiders will not bite unless provoked by intense harassment or accidental contact such as being sat on or otherwise trapped. It’s wise to keep your garden shoes and boots inside, since a dark damp place is a favorite for black widows and ground dwelling spiders. If you stick a toe into a shoe and corner a spider, she will potentially bite in self-defense. Although some are more aggressive than others, as with almost every wild animal spiders would prefer to run away rather than to bite you. The native black widow is Montana’s only venomous spider of concern and if you think you have been bitten by one of these spiders, seek medical treatment. Be aware that as the days shorten in late summer, spiders may seek the protection of your home. (Unless they are black widows that can be a good thing.) Happily, according to Laurie Kerzicnik at Schutter Diagnostic Lab, scientists have determined that hobo spiders are not harmful to humans. She also reminds us that venomous spider bites are extremely rare in Montana and she points out that if the spider’s fangs even manage to pierce the skin, the infection following the bite can often be more dangerous than the venom itself. The non-native brown recluse cannot survive our cold temperatures, but could potentially hitchhike in on luggage. The bite from this spider can be dangerous, because it can become necrotic and seriously infected. Always seek the opinion of a doctor if you have any insect bite that causes concern, but remember that, statistically, more people in the U.S. are killed per year by dog bites (28) and cows (20) than black widows (7).

The next time you see a spider and panic, think of Charlotte, the benevolent spider. Spiders are beautiful, complex animals who are peaceful and relatively harmless to humans, and perform a vital role in the web of life.


Respectfully Submitted by Ann McKean

Master Gardeners at Billings Public Library


On Friday, April 13th, fifteen creative and ambitious Master Gardeners plus some of their family members used the Community Room at the library to host a Family Fun Night. it was open to the public with approximately 50 people in attendance. Educational displays on square foot gardening, garden tools, wise water use, pollination, good bugs, praying mantis, pine beetles and the Master Gardener Program were set up around the room.

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Merita talking with young girl

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Butler telling participants what he did

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Pat answering questions about African violets

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Karen H. at geranium table

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Vonnie heling with children’s activities.

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Casey D. and Cindy R.

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Pat M. and actors Bee, Ron, Merita and Joann

Library 1

Sharon Y. greeting guests

Those in attendance were told about the Master Gardener program and treated to a short skit “What is this?” in which they tried to determine who was telling the truth. The main activity for the evening was getting the audience to solve the Mystery at Orchard Manor as to why some plants were not doing well and who was responsible. Furthermore, there were children’s activities, drawings for gardening prizes, and snacks. Guests went home with zinnia plants, bulbs, square foot gardening packets and educational hand outs. This educational and fun event was immensely enjoyed by the participants as well as the volunteers.

~Submitted by Elaine Allard
~Photos by Joan Griffin

Pollinator Day at St Andrew Community Garden

Master Gardner Dave Kimbell was part of the program at St. Andrew Community Garden Pollinator Day event on June 23. He also did an interview with Terry Moore which is available to watch on YouTube, The garden is in its sixteenth year and has 140 plots (it began with 40)! It includes a mission garden from which produce is donated to area social services.

Book Review: Our Native Bees

Our Native Bees
By Paige Embry

Say “bee” and most people think of honey bees. There has been a lot of press devoted to the plight of honey bees in recent years as the number of hives declines and people worry about getting crops pollinated by traveling honey bee hives if there aren’t enough to go around.

Our Native Bees is about the “other” bees—the natives. Honey bees are not native to America—they come from Europe. There are over 4000 species of native bees in the U.S. and Canada. The author, in part, wrote this book to answer the question of whether the natives can fill in adequately to pollinate our plants if the honey bees disappear.

our native bees 3.pngThe first half of the book is devoted to the relationship of bees with agriculture and speaks to the question of whether natives can fill in for honey bees, and the second half is about the natives themselves, as well as ways to increase habitat for all bees. Along the way, every page is filled with interesting and captivating anecdotes of Paige’s quest to learn about bees and facts about bees that we wouldn’t ordinarily know. For example, ground nesting and being solitary is normal for native species. Many natives are small, even as small as a grain of rice. Most native bees don’t sting. And the majority of flowering plants rely on animal pollinators and the main pollinator is bees.

The book is filled with page after page of gorgeous photos of bees. The photography is absolutely spectacular and as fascinating as the narrative.our native bees 2.png

Both food (think flowers) and nesting sites are important to encouraging healthy native bee populations. When we think of creating a bee-friendly garden, we mainly think of the flowers we can plant. The author points out that providing nest opportunities is just as important (and sometimes can be  “unsightly” to a tidy gardener). There is an important chapter devoted to making golf courses and lawns more bee-friendly in ways that support the bees and are still usable and enjoyable to the people. In the first part on bees and agriculture, she describes how large fields with monocrops, herbicide usage and machine tillage are hard on all kinds of bees and she describes a farm with smaller, more diverse operations and why this encourages diversity of bees as well.

The more we understand the natural world in and around our gardens, the better we can garden in ways that support that world, as well as grow food and provide beauty. Learning about our native bees is a good place to start.

Book Review by Ann Guthals