Linda Tomlinson

Linda Tomlinson

Gardening: Common houseplant pests and what to do about them

Plants are moved inside in the fall and regardless of how careful one is, insects might be hidden in the foliage. It usually takes a couple of weeks in a warm environment for the insects to become noticeable. Aphids, spidermites, and thips are the usual culprits.

The first sign of aphid activity is often a sticky substance on the top of the lower leaves or the surface around the plant. If found, look at the underside of the plant leaves for aphids and their eggs. Aphids are a pear shaped soft body insect that can be various colours and may or may not have wings. In the right conditions aphids can hatch, molt up to four times and start laying eggs seven to eight days after hatching. Adults can lay up to 80 eggs a day meaning that the aphid population can get out of hand very quickly.

Blasting the infected plants with a strong stream of water can dislodge many of the insects. A soap insecticide, and horticultural and neem oils are also recommended. Follow the instructions on the container and keep applying until all the eggs are either hatched or removed.

Mottled yellow and green leaves can indicate that insects are feeding on the leaves. If there are fine webs within the plant then spider mites are causing the damage. Spider mites are very tiny and can be hard to see without a magnifying glass. They can look like a small speck until they are nudged and they crawl away. Their eggs are laid on the underside of the leaves near the plant veins. In a perfect environment it can take eight days from an egg being laid until the insect matures and can lay eggs to produce the next generation. The female lays up to 20 eggs a day for four weeks. Like with aphids, keeping on top of an outbreak is essential. As spider mites dislike a moist humid environment, washing and misting the plants often is a good starting place. Insecticidal soap used regularly for a period of weeks can be effective.

Thrips are another sucking insect that will feed on leaves and flowers leaving them disfigured. Thrips are small, approximately one twentieth of an inch, making them hard to detect. The University of California’s agricultural program suggests shaking or beating a branch to dislodge insects onto a light coloured paper to confirm their presence. In a warm area such as a house or greenhouse a thrip egg can hatch morph through four life stages, two of which feed on a plant, and become an adult in 14 days.

There are many different varieties of thrips but the basic treatment for indoor thips is similar to aphids and spider mites.

Mealy bugs are white fuzzy creatures that are often found where the leaves join the stems. Their eggs are white spots laid on the underside of leaves. Insects and eggs can be dislodged by a strong stream of water or picked off with cotton sticks and rubbing alcohol. Check the plant often to ensure that all eggs and adults are removed.

The best way to check for insects is with a magnifying glass in bright light as they are often hard to spot with the naked eye. If the infestation is out of hand, it can be best to toss the plant and replace it at a later time.

Linda Tomlinson has gardened in Central Alberta for over 30 years.