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Protecting indoor plants from thrips, other pests

Indoor plants bring life, beauty, and cleaner air to our homes, offices and areas across campus. They may also attract unwanted pests like thrips, spider mites and mealybugs. These pests can cause significant harm to your plants: discolored leaves, stunted growth and even plant death. Infestations can occur on plants in private offices and common areas and periodically on purchased or donated plants. Plants that live outdoors for part of the year may harbor stowaway insects when transitioning inside for the winter. Cutting flowers and herbs from the garden to bring indoors is another way they can infiltrate your domain. Let’s discuss recognizing, protecting and treating indoor plants from thrips and other pests.

Recognizing thrips and other pests

Numerous varieties of tiny insects suck the sap out of plants causing damage to leaves, stems and flowers. They can be challenging to spot, but look for:

• Tiny, moving dots: Thrips may be less than 1mm long and can be white, yellow, brown, or black. They have a narrow and elongated body and a pointed abdomen. You may also see tiny black dots on the underside of leaves, which may be fecal matter where bugs have been feeding.
• Distorted, discolored, or damaged leaves: Thrips can cause leaves to become curled, mangled, or deformed in appearance. They also may cause unexplained damage or blackened tips on unfurled leaves. Silvery, white, or rusty discoloration of leaves is common with infestations.
• Fuzzy or cottony patches: Mealybugs and spider mites can produce white, cottony patches on leaves and stems, as well as "webbing" that is present with spider mite infestations.

Protecting your plants

Prevention is the key to maintaining pest-free and healthy indoor plants. Try this:

• Inspect plants before bringing them home or to your office: Check for signs of pests or diseases before introducing new plants to your indoor space.
• Use clean potting mix, pots, and tools: Fresh potting mix is essential. Do not reuse soil from another plant. When reusing a pot, wash and disinfect it, allowing it to air dry before planting. Clean your tools between plants.
• Monitor your plants regularly: Make a habit of inspecting your plants for apparent signs of infestation or disease, but also look closer. Check under leaves for black specks, discoloration, and moving "dust ."
• Leaf washing: gently wash leaves with a mild soap solution or water regularly, focusing on the undersides of the leaves where pests are more likely to hide.
• Ensure good airflow: Appropriate plant spacing can help. When too crowded, airflow to each plant decreases, increasing the chance of mildew production and infestations. Pests can spread more easily in close proximity to other plants.
• Consistent watering: Overwatering can attract certain pests and be detrimental to your plant, creating the likelihood of fungal infections and root rot. Dried out or stressed plants are attractive to indoor pests.
• Maintain optimal humidity: Thrips, mealybugs, and spider mites thrive in dry environments. Using a humidifier or placing plants atop a tray of gravel and water can create a more suitable microclimate. Misting tropical plants periodically also helps keep them refreshed.

Treating infested plants

If you do find pests on your indoor plants, do not panic. Take these steps:

• Isolate the infested plant/s: Remove the affected plant from other healthy plants to prevent the pests from spreading. Check all surrounding plants for signs of infestation and isolate any other plants infected.
• Prune back the infested areas: remove infested portions of the plant to prevent spread.
• Use insecticidal soap or neem oil: These gentle, non-toxic pesticides can help control pest populations. Use as directed, ensuring that the entire plant, including the undersides of leaves and soil, is wet.
• Increase air circulation and humidity: ensure plants are spaced, have good airflow, and receive enough moisture. A humidifier and lightly flowing fan may work wonders.
• Consider a biological control: Introduce natural predators such as ladybugs or lacewings to control pest populations.
• If you prefer, try natural remedies. Natural options may be helpful, such as diatomaceous earth, cinnamon powder, and garlic spray. Research natural remedies and their effectiveness before attempting to use them.
• Discarding the plants: While this can be difficult for a plant owner, it may be necessary. Curing plants of infestations is not easy. Consider this option if the infestation and damage are severe or you cannot provide consistent treatments to the affected plant over several weeks to months.

With patience and persistence, you can enjoy beautiful, pest-free indoor plants all year round.

The ²ÝÁñÉçÇø Facilities Services/Grounds Department can help assist through its Indoor Plant Program. Feel free to reach out directly to jlmagnetek@alaska.edu with any concerns regarding indoor plant care. The IPP webpage also has information on plant care and how to identify and treat pests.

This article was written for use at ²ÝÁñÉçÇø by Juanita Magnetek, the Indoor Plant Program manager and Facilities Services/Grounds horticulturist.