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Yard and Garden: Bugs in Holiday Plants
By: Richard Jauron and Greg Wallace, ISU Extension and Outreach - 12/05/2017

The holiday season is here, and with it comes festive holiday plants. However, these plants may bring along uninvited guests -- insects and other pests.

Iowa State University Extension and Outreach horticulturists offer tips on dealing with bugs on holiday plants and related issues. To have additional questions answered, contact the ISU Hortline at 515-294-3108 or hortline@iastate.edu.

There are tiny bugs on my Christmas tree. What should I do?

Aphids and spiders are the two most commonly found pests on fresh-cut Christmas trees. In both cases, adults that were on the trees back in late summer or fall laid eggs on the stems or needles. These eggs normally remain dormant through winter due to cold outdoor temperatures, but hatched when exposed to warm temperatures inside the home. An infestation may vary from just a few to several hundred individuals.

None of the insects or spiders that emerge after being carried in on a fresh-cut tree will cause any harm or damage to the tree, the house, the furnishings or the occupants. They cannot bite or sting and will not live long enough to grow or multiply. The tiny insects or spiderlings are simply an annoyance.

Do not spray insecticides on fresh-cut Christmas trees. The insects and spiders will quickly die of starvation or desiccation, whichever comes first. If newly hatched insects or spiders are found on the floor or other areas around the tree, simply vacuum them up and discard them.

Small, white insects flutter about my poinsettia when I water the plant. What are they and how do I control them? The small, white insects are likely whiteflies. Whiteflies are common insect pests of poinsettia, hibiscus, chrysanthemum and a number of other indoor plants. They most often are noticed when watering or handling a plant. When disturbed, whiteflies flutter about the plant for a short time before returning to the plant.

Whitefly adults are small, white, moth-like insects. Female adults lay eggs on the undersides of plant foliage. After five to seven days, the eggs hatch into small, pale green, immature insects called nymphs. The nymphs crawl a short distance before settling down to feed. After feeding for two to three weeks, the nymphs progress to a nonfeeding stage and then finally to the adult stage.

The nymph and adult stages of whiteflies feed by inserting their short, needle-like beaks into foliage and sucking out plant sap. Heavy whitefly infestations may cause stunting or yellowing of leaves, leaf drop and a decline in plant health.

Whiteflies on poinsettias and other indoor plants are extremely difficult to control. Prevention is the best management strategy. When purchasing plants, carefully check for whiteflies and other insects. Avoid purchasing insect-infested plants. Insecticides are not a good control option as they are not very effective. It's often best to tolerate the presence of a small infestation of whiteflies on a poinsettia and then promptly discard the plant after the holidays.

There are small, brown "bumps" on my Christmas cactus. What are they?

The Christmas cactus may be infested with scale insects. These small insects are covered with scale or shell-like, waxy coverings. They attach themselves to stems or leaves and suck sap from plant tissue.

The life cycle of scale insects consists of the egg, nymph and adult stages. Eggs are laid below the scale coverings of adult females. When the eggs hatch, the nymphs crawl from underneath their mother's scale and move a short distance to their own feeding site. The newly emerged nymphs are also called crawlers. At their new locations, the nymphs insert their slender stylets (mouthparts) into the plant and begin sucking sap. The covering or shell develops soon after feeding begins. Scale insects remain at these feeding sites for the rest of their lives.

Scale insects are difficult to control. Systemic insecticides are generally ineffective. The shell-like covering protects scale from contact insecticides. Contact insecticides are only effective when applied during the crawler stage (before the insects develop their protective shells). Since it's difficult to determine when crawlers are present, scale-infested plants will need to be sprayed with insecticidal soap every seven to 10 days until the infestation is eliminated. Small infestations can be controlled by individually scraping off the scales or by dabbing each scale with an alcohol-soaked cotton swab.

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