Cool Weather and Indoor Insects

September 17, 2018

So much focus is placed on prevention and extermination of warm weather and outdoor bug problems like Japanese beetles, squash bugs and various caterpillars, it’s easy to forget that there are a few pests that threaten our plants year round, inside and out. These opportunists take advantage of mild days throughout the year outdoors, and can cause problems indoors at any time.




Aphids are soft bodied insects that may be found around new growth, along leaf stems or on the undersides of leaves. They are normally green, but may be yellow, grey or red. They suck the juices out of plants and may cause yellowing or distortion to young foliage. As with whitefly, they may be accompanied by deposits of honeydew and sooty mold. Often ants will be attracted to these deposits, but rest assured it is not the ants but the aphids doing the real damage. Blast aphids with a strong jet of water to reduce population size, then spray with horticultural oil to kill the rest.



Fungus Gnats

Fungus gnats are small black flies that live in and around the soil, and may first be noticed flying around well-lit plants in sunny windows. They are merely an annoyance as adults, it is the larvae which in large numbers may damage plants as they may chew on roots. Using pasteurized potting soil and employing good watering habits will minimize the likelihood of fungus gnat problems. Always ensure good drainage, and let the soil surface dry out between waterings. To control heavy populations, use yellow sticky traps for adults and spray the soil with BTi or a pyrethrum based insecticide.




Mealybugs are white, cottony-looking masses that often form in the intersections where leaves meet stems, or on the underside of leaves. A closer look reveals the gray bugs in the midst of a white mass of waxy, web-y stuff. Mealybug damage is quite similar to that of scale: yellow leaves and stem dieback. The bugs are a bit more mobile than scale, but still may be removed, along with their messy creation, using a cotton swab dipped in rubbing alcohol. Horticultural oil is a good treatment for infestations here as well.



Scale are plant-sucking insects with heavy, waxy coatings over their bodies. They are often found on stems and leaves, and look like scabs or scars to the untrained eye. These bugs are relatively inconspicuous until large groups are present which cause yellow leaves and branch dieback. Inspect houseplants regularly, checking stems and both top and bottom surfaces of leaves. In the landscape, pay particular attention to the most susceptible plants like euonymus. Scrape off individuals with your fingernail, or apply horticultural oil at the first sign of infestation.




Whitefly is just what the name sounds like: a tiny white fly. The indication here is a small cloud of these creatures taking flight when you brush against the plant or the foliage is otherwise disturbed. Symptoms include yellowing and distortion of new growth on which they feed, as well as sticky honeydew deposits on which black sooty mold will grow if left untreated. These prolific creatures can be difficult to control due to the adults’ mobility. Isolate infested plants. Use yellow sticky traps to catch adults. Blast affected areas of the plant with a strong stream of water to reduce large populations. Spray with horticultural oil or insecticidal soap every week to ten days until the infestation is in check.

Why These Treatments?

The first stage of control is always prevention. Providing good growing conditions like proper light exposure, good air circulation, the right amount of plant food and watering properly for the individual plant’s needs, will go a long way in minimizing the stress that might otherwise lead to unhealthy plants and susceptibility to infestation. In the rare occurrence of insect infestation on a healthy plant, the goal is to act quickly and decisively but not necessarily in a toxic way. Physically removing bugs with a strong jet of water or a cotton swab is extremely effective and non toxic, as such it is the preferred first step in eradication. Horticultural oils and insecticidal soap kill bugs by acting physically, not chemically; and they present extremely low levels of toxicity. When these treatments are applied to healthy plants and weakened bug populations, they are highly successful. The decision to apply a more highly toxic insecticide on a plant with compromised health is one that should not be taken lightly, and the option of replacing the plant should be considered in that process.


Take good care of your plants and yourself. Keep a watchful eye out for bugs that may threaten your garden indoors or out and take action when necessary. You will be amazed at how easy it can be!

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