When aphids strike your houseplants, it’s fairly easy to gain control.
Aphids on the attack

Aphids suck the juice out of tender leaves, flowers, buds and stems, leaving sticky residue and discarded exoskeletons.

Stickiness. Uh-oh. Tropical houseplants jostle for space under the grow lights in my basement from October to May, waiting for the summer warmth to return. Like any population living in a crowded, unnatural environment, these plants are prone to pests and disease. Sticky spots on the foliage usually mean insect pests have found a host.

Okay, where did I leave my reading glasses? Closer inspection reveals white stuff stuck to the leaves. The evidence points to aphids. These insects discard their outer shell or exoskeleton as they grow, leaving an-easy-to-follow trail. They excrete a sticky substance that sometimes attracts ants and can foster fungal disease. The symptoms sound bad, but aphids are one of the less complicated pests to eliminate from houseplants. An examination of the softest new growth on an angel-wing begonia and the blooming African violet next to it confirm my suspicions. Green insects about the size of an o are hard at work extracting juice from my plants. Another plant nearby has orange aphids. I need to wear my glasses more often!

Aphids mostly hang out on branch tips and new leaves, buds and flower stems, which makes them relatively easy to find. The begonia and Africa violet are headed for the bathtub, along with a few of their neighbors, just to be sure I haven’t missed anyone.

I use only botanical and other natural pest controls, such as pyrethrins, neem, and horticultural oils. These work just as effectively as chemical pesticides, with fewer environmental side effects. I spritz the entire plant, including the undersides of the foliage, until the spray drips off. Hence the trip to the tub.

As soon as I moved the plants, though, I noticed small black flying insects. Fungus gnats. These critters spend their grub stage in the soil, then emerge as tiny, annoying gnats that seem drawn to faces and computer monitors. The adults are otherwise harmless, but the grubs can damage plant roots. Fortunately, they are also easy to control because the adults are attracted to the color yellow. I hang yellow cards covered with sticky tangle foot from the grow light fixtures and the problem’s solved. Another option is Gnat Guard, which uses tiny nematodes to control the problem.

For photos of other common pests and diseases and their controls, see our Pest and Disease Finder.

-Ann Whitman
Horticulturist, Gardener’s Supply