Garden with Betty Cahill: Indoor Plants Part II

Houseplant Health Part II

The daily excitement continues as we draw closer to spring and outdoor gardening. Until the dormant shades of outdoor plants come to life let’s focus on indoor plants which provide year-round enjoyment and beauty—most of the time. On occasion insect pests and diseases can rear their annoying heads. Below are some common houseplant ailments and control options.

1) Spider mite pests are extremely small and mostly invisible to the naked eye. They thrive on plants in dry, low humidity indoor and outdoor environments. Evidence of spider mite presence is the silky webbing they make around and under leaves and plant parts. Their straw-like piercing-sucking mouthparts cause visible damage to leaves by removing the green pigment resulting in dull, stippled or a spotted, bleached out appearance. Damaged leaves can also turn silver, brown or yellow and fall off. Severe spider mite infestations may cause plant death. Check for spider mites by tapping leaves over a white piece of paper. If tiny dots move about, then further confirm their presence by folding the paper which will leave smeared red/brown streaks.

Try washing spider mites off household plants with a gentle spray of water in a tub, if possible. Insecticidal soaps, and horticultural oils are helpful, be sure to spray the undersides of leaves.

Spider mites favor Norfolk Island pine, schefflera, ivy, dracaena, citrus, begonia, prayer plant and palm.

Online photo from https://www.plantipeeps.com.au/blogs/planti-how-to/plant-pests-101-spider-mites

2) The mention of fungus gnat pests can cause gardeners to emote from their incessant slow flying around plants and one’s face. A very common houseplant nuisance, fungus gnats are small, ¼-inch, weak black flies that do not bite or cause plant damage. Fungus gnat larvae feed on decaying plant matter, fungi, algae and plant roots in the top 2-3 inches of soil. Their life cycle is short, 3 to 4 weeks from egg to adult, with year-round reproduction. One adult female can lay up to 200 eggs in her short ten-day life in houseplant soil and cracks.

Fungus gnats are more of a cosmetic and flying annoyance than a cause for plant damage.

Online photo from https://plantperfect.com/how-to-deal-with-fungus-gnats-on-houseplants/

Fungus gnats prefer moist soil for egg laying. One control is to let soil media dry before each watering. Consider adding a thin layer of coarse sand or tiny rock over the top of the soil which discourages egg laying. An easy to find product sold at garden centers and online is a natural occurring bacterium called Bacillus thurengiensis israelensis, or Bti for short, which kills fungus gnat larvae.

Bti is also effective for use on mosquito larvae outside in water features and is labeled as being safe around people, pets, plants and livestock.

Another idea is to try sticky yellow cards to trap adults (and other pest insects.) Fungus gnats can be issues for just about any indoor houseplant.

Photo by Betty Cahill

3) Two types of round to oval shaped small scale pest insects look like tiny bumps on leaves and along stems. Armored scale pests are 1/8 inch long with a hard, protective shell; soft scale, a bit larger, are covered with a thick, waxy coat. Adults do not noticeably move about plant leaf and stem surfaces. Females lay eggs under the protective coating, but in their “crawler” stage they move and find a feeding site and develop their protective shell.

They feed on plant sap in plant tissue leading to reduced overall vitality. Leaves can turn yellow, wilt and drop prematurely. Severe, prolonged damage can cause plant death. Their honeydew excrement causes shiny stickiness around plants, furniture and nearby floors.

Small infestations of scale pests can be removed by carefully picking or scraping them off the plant with a soft bristled toothbrush, or dab each scale insect with an alcohol-soaked cotton swab or Q-Tip. These are difficult pests to kill; insecticidal soaps and horticulture oils can provide some control.

Scale insects favor bay leaf, schefflera, citrus, ferns, crotons, snake plant and Ficus.

Online photo from https://www.gardeningknowhow.com/plant-problems/pests/insects/control-plant-scale.htm

4) Environmental conditions are more often the cause of indoor plant diseases and not often found on plants that are healthy and thriving. Make sure plants are getting what they need in terms of appropriate light, water, fertilizer, soil quality and drainage. Too little or too much of any of these conditions weaken and stress a plant’s vigor and make it more prone to disease.

Practicing good plant housekeeping is a very good habit to adopt. When plants show signs of trouble, try grooming the plant where there are issues. Remove fallen leaves and flowers promptly, quarantine plants that are suspected to have an issue until it is resolved. Avoid splashing water onto plant leaves, and protect plants from direct heat vents and cold drafts.

Diseases can arise so consider taking photos of troubled plants, up close and a full profile. Show the photos to your reputable garden center expert or nearby Colorado State University Extension office or online help desk for diagnosis. Be prepared to answer questions about the plant’s growing conditions and your care routine.

Other Tips

Read all label application instructions when using insecticidal products on indoor plants. Try to spray outside if it is not too cold.

If possible, use various non-chemical options instead of just one method.

Avoid introducing pests into homes by first inspecting newly purchased plants or ones brought inside after the summer season. If insects are present, isolate the plant and use control measures.

Humidity can be slightly increased by placing houseplants on a small pebble tray where water sits below the pebbles and not directly in contact with the bottom of the plant. Plants grouped together can boost humidity.