Whiteflies secrete a sticky, 'honeydew' substance
Q. I recently noticed an area of sticky residue next to the south window where I keep my houseplants for the winter. Is this natural? My plants appear to be weakening and experiencing leaf drop.
A. A likely cause for your sticky floors is an infestation of sapsucking insects that secrete a "honeydew" that is sticky as described. Whiteflies, aphids and mealybugs all secrete honeydew.
Gently shake the plant and watch for tiny white flies. Also check the undersides of leaves.
Whiteflies are abundant worldwide and cause substantial crop damage. These insects not only cause damage by injecting toxic saliva into the host plant, but also they are vectors of numerous plant diseases such as mosaic and leaf curl. Heavy whitefly infestations cause plants to lose vigor, experience leaf drop and become susceptible to diseases. This would cause yellowing leaves and weakened plants.
Always practice "integrated pest management" outdoors; i.e. use pesticides as a last resort after trying other methods - mechanical, cultural and biological. Control of whiteflies outdoors is aided by the fact that there are many natural predators: hummingbirds, wasps, ladybugs, and lacewings.
Be aware that the most effective pesticides are neonicotinoids and these can have a negative impact on bees and other wildlife. Outside, the goal is to manage the population without pesticides so that natural biological agents will control the infestation.
Whiteflies in your house are another matter. Your goal is to eliminate all of them. Since there is no concern for biological controls inside your home, insecticidal soap, pesticides or home remedies can be applied, but carry out all applications outside of your living area.
Since whiteflies prefer the underside of leaves for feeding, smaller houseplants can be rinsed off in the kitchen sink by using your sprayer. Larger plants can be rinsed down in your shower by wrapping a large plastic bag around the pot so the earth is not washed out. Weather permitting, this can be done outside.
The next level of control is pesticides. Again, the simplest and safest would be any of the insecticidal soaps available at any garden center. Be certain to keep plants out of direct sunlight after a spray and do not reapply too frequently, as this may cause burns and stunt growth. As a last resort, stronger pesticides can be used, but be sure to follow the instructions for use carefully and dispose of the empty container properly. Several applications of whichever course of action you choose will most likely be necessary.
Once eradicated indoors, be sure to examine any plants that have spent the summer outdoors for whiteflies, especially on the undersides of the leaves, before bringing them back into the house. Also inspect any bedding and vegetable plants you purchase from your garden center to avoid bringing home any unwanted guests. With any bit of luck, you will be able to control this common pest.
- Matt Steichmann
• Provided by Master Gardeners through the Master Gardener Answer Desk, Friendship Park Conservatory, Des Plaines. Call (847) 298-3502 or email northcookmg@gmail.com.