How to deal with flying insects when watering
DEAR GARDEN COACH >> I am new to growing houseplants and seem to have a lot insects flying around when I water. What are they, and can you recommend nontoxic solutions. I have kids and pets.
— Hannah V., Sunnyvale
DEAR HANNAH >> What you have on your houseplants is fungus gnats; a fly that is part of a larger family of flies in the Sciardae family. Fungus gnats love to lay their eggs in rich, damp soils, which often poses a problem to commercial growers because the larvae can wipe out seedlings, cuttings and young plants. It is possible that you came home with eggs or larvae already in your soil.
Fungus gnats, like other flies have four stages in their life cycle: Larva, (with four larval stages or instars), pupae, and adult. The adults live for about a week, but in that time they can lay up to 300 eggs into the soil. Damage occurs in the larvae (eating) stage because they feed on the root hairs of the plant, weakening it because it inhibits the plants ability to intake water and nutrients.
The larvae live for about two weeks and then pupate, which is the stage when they change from a maggot to a fly. This stage lasts about three to five days when new adults emerge to begin the whole cycle again.
Because most soil mixes used in propagating houseplants are predominately peat moss, I repot my plants after purchasing with a mix containing less peat. Peat moss retains water, and when combined with overwatering a moist, warm environment occurs and this is what many diseases and pests like the gnat fungus thrive on.
To avoid overwatering allow the soil surface to dry out a couple of inches between watering. Dry soil will kill the larvae and make an environment less conducive for the eggs to mature. To ensure you don’t come home with fungus gnats inspect the plants before you purchase by gently moving the soil near the base of the plant. If you see gnats flying around or the larvae, which is a whitish color do not purchase.
Here are effective, nontoxic products you can find at local hardware stores or nurseries:
• Yellow sticky traps placed horizontally on the soil surface will attract and kill the adults. Beneficial nematodes are microscopic round worms that penetrate fungus gnat larvae and kill them.
• Gnat Nix is made from crushed glass and used as a top dressing on plants creating a barrier against the fungus gnats.
• Mosquito Bits, a favorite for greenhouse growers because when sprinkled on to the soil it kills larvae within 24 hours. Mosquito Bits contains Bacillus thuringiensis, a microorganism that produces chemicals toxic to insects.
DEAR GARDEN COACH >> I want to grow things from seed, but each time I start them they come up, but then overnight they fall over right at the stem and soil. Is something eating them?
— Margery Smith, Vallejo
DEAR MARGERY >> It sound like you might have damping-off disease. According to the University of Minnesota, the fungi, Rhizoctonia spp. and Fusarium spp., along with the water mold Pythium spp., are the most common pathogens responsible for damping off. For more information about best practices for raising seedlings, visit their website https://www.extension. umn.edu/garden/yard-garden/diseases/damping-off/.