Pest Management for Houseplants
By Brenda Ortmann, Anoka County Extension Master Gardener
When the nights begin to dip below 50 degrees, it is time to lug all those beautiful non-hardy house plants back inside. Along with your plants, you are bringing in whatever may have found a home in their leaves or dirt during the summer, including weed seeds, fungi spores, bugs, and insect eggs.
You can pull germinating weed seeds or rake over mushrooms that pop up in houseplants, but bugs can be difficult to control depending on the type of insect and whether the infestation is new or well established.
The best way to deter pesky home infestations is prevention. A few days before bringing plants inside, bathe them using a mixture of 1 tsp neem oil, 1 tsp mild soap, and 2 cups water. Using a spray bottle, douse the leaves from above and below, and saturate the soil. Next, take a paper towel or rag and rub both sides of each leaf. Neem oil causes phytotoxicity in plants, so keep them in the shade during treatment. You can bring your plants inside once the leaves dry.
If you’ve already brought your untreated plants indoors, have no fear. Late is better than never. Bring the plants you had outdoors into the shower, and follow the same treatment process. After the initial cleaning, lightly spray this mixture on plants and soil weekly as a preventative. Homemade neem mixtures degrade over time, so fresh is best.
If an indoor infestation is already present, quarantine your affected plants in the shower and douse them in the neem oil mixture. Do a preventative treatment on surrounding plants. Neem oil mixtures or horticultural sprays are effective at combating aphids, thrips, scale, and spider mites.
For mealybugs, use 70% isopropyl alcohol diluted to approximately 25% and mist the plant and soil. Spot treat any visible pests with an alcohol-saturated paper towel or cotton swab. Repeat the process weekly until no more pests are visible.
Another common pest are fungus gnats. They lay eggs in the soil, which emerge and become a flying nuisance in the house. Methods to decrease their population include sprinkling sand on the soil, using sticky traps, and/or applying a biological organic larvicide (Bacillus thuringiensis israelensis) as directed on the bottle.
A final way to deter most pests is to use a systemic treatment such as imidacloprid. Follow the directions exactly as stated on the product label. Note that systemics will not prevent spider mites, which require either neem or horticultural oil to fend off or eradicate. Systemics get absorbed by the plant and are not pollinator friendly, so stop use several months before moving plants back outside to protect our pollinators.
Some pests are persistent once established, so you might need to gauge your willingness to put forth the effort to eradicate your unwanted visitors. Sometimes it is easier to dispose of the plant (outdoors) and start over. However, if a plant is especially meaningful to you, it is often worth the effort to save it.
Save the date for the Home Landscape and Garden Fair on April 2, 2022 at Bunker Hills Activities Center in Andover, MN. For event registration and information about Anoka County Master Gardener projects and services, visit anokamastergardeners.org