When scale infests a plant in sufficient numbers for you to begin to see damage, it is very likely that the plant was already experiencing some degree of stress. Most plants that are truly healthy don’t seem to have scale problems. Pest insects prefer to go after weakened plants that are struggling and lack vigor. Often it is the very young or older plants that are targets. Researchers examining the effects on insects of glutathione, a chemical produced by stressed plants have found that it actually benefits certain harmful insects, aiding their reproduction, growth, and possibly bolstering their ability to resist pesticides. This may explain why scale is attracted to struggling plants.
Some Causes Of Plant Stress
Part of the treatment for scale problems is prevention. Try to determine possible sources of your plant’s stress and correct them. Some causes of plant stress include:
Too much or too little sunlight or water.
Inappropriate plant for your climate or local soil conditions.
Overuse of fertilizer which encourages excessive leafy growth.
Drastic pruning which stimulates growth of succulent suckers.
Use of pesticides against other pests which also kills off natural predators.
Transplant shock which lasts for a few days up to a week.
A cyclical scale population explosion prior to emergence of natural predators.
Attacks by other pests or disease organisms