The orchid family (Orchidaceae) contains over 20,000 species valued for their colorful flowers. Vibrant orchids attract various scale insect species, with the boisduval scale (Diaspis boisduvalii), elongate soft scale (Coccus longulus) and soft brown scale (Coccus hesperidium) being the most problematic. You can get rid of all types of orchid scales using various environmentally friendly treatments.
Scraping Off Scales
Before using any type of scale treatment, help the process along by gently scraping visible adult pests from the foliage using your fingernails. Wear rubber gloves if you don't want to actually touch the pests. Adult scales look like little yellow to deep brown spots on orchid leaves and stems.
An adult female scale lays up to 200 eggs which remain underneath her shell even after she dies, so removing adults and their coverings helps prevent future scale infestations.
Wiping With Alcohol
Small scale populations can typically be removed by dipping a cotton swab, soft cloth or soft-bristled toothbrush in 70 percent isopropyl alcohol and wiping it over all foliage surfaces, including stems, tops and bottoms of leaves, leaf edges, midribs and other veins.
Allow the alcohol to evaporate for two to three hours before rinsing the leaves with water. However, if you're treating orchids outdoors on a windy day, you should immediately wipe the alcohol off the foliage using a soft, clean cloth. Ample air circulation causes alcohol to evaporate very quickly, which can cool treated plant tissue to the point where it kills cells.
Repeat applications every seven to 14 days to eliminate new crawlers, which typically look like tiny yellow dots moving across orchid leaves.
Spraying Neem Oil
Larger scale populations might need a spray with a little more killing action. Neem oil is an ecofriendly choice that smothers scale insects without impacting people, pets, beneficial insects or birds.
Make a solution containing 1 teaspoon of neem oil and 1/2 teaspoon of mild dish soap in 1 quart of warm water. Use a small spray bottle to completely coat all orchid foliage, including the tops and undersides of leaves and around plant bases.
Repeat applications every seven to 14 days until no more new scales appear. Reapply oil sprays after rainfall or overhead watering.
To reduce the risk of leaf burn, avoid spraying orchids outdoors if the temperature is above 85 degrees Fahrenheit.
Neem oil can harm honeybees if it makes direct contact, but it no longer affects the pollinators once the spray dries. If treating orchids outdoors, spray oil in the late evening or early morning hours when bees won't be buzzing around the flowers.
Treating With Soap
Insecticidal soap is another scale treatment that dehydrates pests while offering low toxicity for humans and animals. Read the soap product's label to make sure it can safely be used on orchids and, as always, follow the manufacturer's directions.
One product recommends mixing 2-1/2 fluid ounces of soap concentrate with every gallon of water. Thoroughly cover all plant surfaces until wet. Repeat applications once a week for up to three weeks to kill newly hatched scales. Rinse the foliage with clean water if plants start wilting within three hours of treatment.
The St. Augustine Orchid Society reports that scales can become resistant to pesticides, so don't use the same treatment more than four times in a row.
Although alcohol, neem oil and insecticidal soap treatments are all ecofriendly solutions, the substances can still damage sensitive orchids, particularly tender, young leaves. Test any solution on a single leaf and allow it to stand for at least overnight before checking for injury. Only treat entire plants if no burning occurs.
Never apply liquid treatments to plants sitting in direct sunshine. Instead, treat orchids in a shady spot and keep them in the shade until the solution dries.
- Put on protective clothing and eyewear before mixing and applying scale treatments, and keep everybody away from treated plants until the solution dries.
- Photo Credit Medioimages/Photodisc/Photodisc/Getty Images
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