Now that we’re firmly into autumn, it’s time for greenhouse growers to prep their plants for possible wintertime troubles. Don’t let mealybugs turn your horticulture into their holiday hideaway.

Mealybugs (Pseudococcus spp.) are common plant pests. They are sucking insects that feed on leaves, buds, flowers and stems. They leave behind discolored, often yellowish, leaves and honeydew, a clear and sticky excrement that can grow a sooty-textured mold. An infestation of mealybugs can be detrimental to a plant, causing it to decline. Flower buds tend to drop off before blooming when affected by mealybugs, reducing the plant’s beauty and productivity.

The adult males are winged and tiny, and the adult females have segmented bodies that look fuzzy and like they are covered in wax. These insects can reproduce asexually without mating, which means a grower can have a high population of mealybugs in a relatively short time.

Mealybugs. Photo courtesy of U.S. National Collection of Scale Insects Photographs , USDA-ARS, Bugwood.org

Most species of mealybugs lay several hundred eggs in sacs resembling wads of cotton attached to plant parts and can produce anywhere from two to six generations a year depending on their environment. All stages of mealybugs – egg, nymph and adult – may be present simultaneously when indoors or in warm climates.

When outdoors, insect pests have natural enemies such as birds, other insects and cold weather. But when growers begin keeping their plants indoors, mealybugs can thrive while feeding on their plants. Here are some tips to help your plants:

Clean Your Plants

Carefully inspect and clean your plants to avoid the possibility of contaminating your entire inventory with mealybugs looking for a safe haven.

  • Clear away debris from the soil surface of potted plants.
  • Prune back stems to restore the plant’s form and remove dead leaves and spent flowers.
  • Wipe off pots and wash saucers in hot, soapy water – mealybugs are often found on the underside of saucers.
  • Wash small plants in the sink. Wash larger plants in a shower or with a sprayer attached to your garden hose. Be sure to rinse the undersides of the leaves to clear off pests as well as egg masses, dirt and cobwebs.
  • Treat with pesticides labeled for houseplants and indoor ornamentals such as insecticidal soap.
  • It’s unlikely that all mealybugs will be eliminated on the first attempt, so keep inspecting your plants on a regular basis and repeat these steps as needed.

Autumn may also be a good time to consider repotting your plants. While the plant is out of the pot, turn the plant around and upside down and look for mealybugs and other pests on the underside of the leaves. Using a damp paper towel or cotton swab, wipe off any insects, webs or egg sacs you find.

And don’t try to save one plant if it risks your entire supply. You should be able to recognize when, despite your best efforts, you have a plant that is too infested to salvage. It is not worth chancing the mealybugs spreading to your other healthy plants. Know when to consign a lost cause to the compost pile and take the opportunity to replenish your stock with replacement plants.

by Enrico Villamaino