Trees are precious resources that add beauty to the landscape and help clean our air. Some trees are resistant to pests and disease, but most have an "Achilles Heel" of some sort. Pest infestations can cause heavy damage on trees, especially crop and groved trees where infestation can spread. Crop trees require insecticides that are approved for use on consumables. All tree insecticides should be safe for the environment and use around people and pets.
Scale insects can be hard to see on trees. They occur as small bumps barely perceptible to the naked eye. The have a shell over their body that protects them and move very little. There are two types of scale: hard body and soft body. Hard scale creates a covering constructed of wax and shed skin over itself which can be separated from its body. Soft scale has a similar armor, but it is attached to the insect body. Soft scale produces honeydew and hard scale does not. Both insects suck plant fluids from limbs, trunk and branches. They can cause significant damage in the long term. Scale is a difficult pest to eradicate just using mechanical methods and usually requires an insecticide for permanent control.
Imidacloprid is a generally accepted control for scale. It comes in a granular form that can be worked into soil to gradually leach into tree roots. It is systemic so it will travel the vascular system and infect the scale as they suck plant juices. The Bayer Advanced Garden line of products has an excellent granular called "Tree and Shrub Insect Control," which contains Imidacloprid. The benefits of the product are that it is very effective, is low in toxicity and keeps working long after application. Unfortunately, its effectiveness against some pests can cause an increase in spider mites who will no longer have predators. Marathon 1 percent granular insecticide also contains Imidacloprid and has shown good control advantages.
This has been a popular insecticide since the 1950s. It works well on scale and a host of other garden pests. It is considered extremely toxic and should not be used on crop trees. It is banned in industrial application because of the toxicity to birds. It needs to be watered in thoroughly after the granules are applied. Care should be exercised, however, because heavy watering will raise earthworms, which attract birds and they, in turn, can be threatened by the poison.
Sevin's Garden Tech granular insecticide contains the active ingredient Carbaryl. It is approved for use on food crops and lawns and is effective on tree scale. It is ready to use and can be worked into the soil for best control. It gives three weeks of control, so regular reapplication will be necessary. Sevin also carries a dust product that will give good scale control.
Safari 20 SG insecticide is a one-two punch for scale. It is provides quick uptake, which means it releases and metabolizes quickly in the tree. It also offers control for most other common tree pests. It can be used on most types of trees and has a long residual life. A higher residual aspect means the product will remain in the ground for longer, so care needs to be taken with exposure to the soil.