Scales are a persistent pest that can be difficult to eradicate. They prefer woody plants and are a problem with many citrus growers with Ficus plants often being infested with scales. The first sign you have a problem will be sick and unhealthy plants. Growth can be stunted and leaves might start to turn yellow. If you look closely at the stems and under the leaves you can find the flat disc-shaped scales and there might be sticky honeydew present. There are both hard (armored) and soft scales. Mealybugs are also part of the scale family.
Scales produce a waxy covering over their bodies that protect them from predators and pesticides. They live under their protective covering while they slowly suck juices from the plant. Hard scales range in size from 1/16″ to 1/8″ while soft scales range from 1/8″ to 1/2″ in diameter. Their color and shape can vary depending on the species, though they are typically circular or oval shaped. There are over 400 different types of scales in the US.
Armored scales lay their eggs under their waxy “shell” with the eggs hatching into “crawlers” after one to three weeks. The crawlers then begin searching the plant for an appropriate place to feed using piercing-sucking mouthparts to penetrate the plant tissue and suck its juices. Female armored scales molt two times before reaching maturity, losing their antennae and legs in the process. They are immobile and cannot move around the plant. The shed skins become part of their protective shell. Soft scale females go through a similar process. They do not completely lose their legs and antennae however they are shortened, making movement difficult. Males go through four molts and, unlike females, go through a pupal stage. They emerge as a small winged gnat-like insect that is not capable of feeding with their sole purpose being to reproduce. Scales can be found all year long, but in cold areas they overwinter mostly as eggs or mated females.
Controlling scales can be very difficult. Their waxy covering offers them significant protection. Mealybug Predators (Cryptolaemus montrouzieri), Ladybugs, Green Lacewings, and Pirate Bugs are all capable of eating soft scales; however they do not eat hard scales. There are also Scale Parasites, such as Aphytis melinus, that attack certain species of scales. Insecticides and organic sprays can be used against the crawler stage. Horticultural oils give fairly good results as they can suffocate even the adults and rubbing alcohol can be applied to individual scales with a q-tip or cotton ball in small outbreaks.
Only the males fly, so to get an infestation the scales usually arrive on plants. Carefully inspect new plants to be sure they are clean of scales. Use a 10X or 16 X magnifiers and look closely on the stems and underneath the leaves. If there are any pests present, try to keep them separate from the healthy plants. Be diligent, and regularly inspect your plants for pests.
Nathan Jackson is the owner of Nature’s Control and Ladybug Indoor Gardens. You can send your specific bug questions to firstname.lastname@example.org. For more information, to request a catalog, or to find a local distributor, visit Naturescontrol.com or call 541.245.6033.