Scale insects look like fish scales or very tiny seashells. They are small (approx. 3mm) and are not mobile and have no visible legs or antennae. They have a waxy coating on their backs.
They attach themselves to stems and foliage of many plants. They can become a very serious problem. There are so many different species (almost 6000!) and they are many different colours brown, gray, black and white. Some cover themselves in fluffs of cotton looking covers. You find them on stems. Here are a few types:
Eunonymus Scale-(top left) Eric Day, Virginia-females pear-shaped and brown, males white, attacks evergreen eunonymus. Cause defoliation and dieback. Obscure Scale-(top right) Eric Day, Virginia-dark gray, appear in groups on stems, attacks oak, maple, willow and many other trees. Cause dieback and can kill entire trees.
Hemispherical Scale-(left) Eric Day, Virginia-brown, smooth and glossy, attacks greenhouse plants and indoor plants. lifecycle is continuous if not controlled as they can not overwinter outdoors. Cottony Camellia Scale-(right) Eric Day, Virginia-long and white cottony masses, attacks camellia, rhodos, holly, roses and many other ornamentals.
Pine Tortoise Scale-(left) University of Minnesota-reddish brown, group in cluster, attracts most pine and evergreen. Needles off coloured and stunted. Oystershell Scale-(right) University of Wisconsin-brownish, attacks lilacs, trees and other shrubs
Diet and Damage
They are sap sucking insects. Attaching themselves to leaves and twigs they suck the juices out of plants. They cause wilting, dieback and can kill entire plants if infestation is severe.
1) Hand Pick
Where you see them (they are difficult to see) crush them with your fingers. You can tell if they are present by a sappy residue on and around plants.
2) Dormant Oil
Dormant oil sprayed in the fall or late winter will help control them outdoors. it suffocates the overwintering larvae. Spray only as directed on the label. Be careful when buying dormant oil because some of these oils contain chemicals that are not organic.
Prune infected twigs before they become a problem and burn the waste.
4) For Houseplants & Greenhouse Plants
Put them outside in the day early in the spring for a few hours. These guys don’t like a temperature variation and they will not reproduce readily.
5) Soap Sprays
There are several different types but be sure you douse the insects or it will not work.
A word on dormant oil spray. Make sure it contains MINERAL OIL and no additional chemicals. Some manufacturers add other chemicals to their sprays (arsenic or sometimes lead) . It can also control some diseases that these pests and others spread. Later’s has a brand that is safe but should not be used near water or fish ponds. However I would recommend making your own.
Here’s my recipe:
1 gallon of light grade oil or mineral oil
2 pounds of fish oil soap-an emulsifier (approximate amount)
(I got my fish oil soap from the local organic gardener but you can buy it at several health food stores, call around)
Boil these ingredients and mix until they thicken. Add at least 20 parts of water. Shake well. Use as soon as possible so the mixture doesn’t separate. (obviously waiting until it has cooled *S*) You can safely spray this in the late fall and again in the spring.
A true story. I had these guys kill my 12 year old fig tree! I had no clue as to what they were until I cut a branch and took it to the local nursery and asked. By this time it was too late and I had a funeral burning party in my yard. They told me that I should have known since I had to mop my floors everyday because of the sticky residue they secrete. Grrrrr…..I hate these guys!