SPRAYING TREES FOR PESTS AND DISEASES
Spraying was used for many years to treat many pests and diseases. Now, sprays are seldom useful for insects because systemic controls are possible without harming beneficial insects. Sprays are necessary for some fungal diseases.
Unfortunately there are many companies that "sell spray" and do spraying indiscriminately. Those companies seem to suggest that spraying can cure all problems. The consumer is at their mercy, regarding them as the "experts" and thus trusting the recommendations they give. Spraying should be done only for specific problems, only if the benefits outweigh the negative effects and only using the specific technique and with the timing demanded by the problem at hand.
We rarely spray anything other than fungal diseases. Occasionally we will spray miticide, but when we do it is NEVER mixed with an insecticide.
WHEN SHOULD SPRAYING BE EMPLOYED?
1. The pest or disease must be specifically identified. General cover sprays of pesticide mixes are never a good idea. The technique, timing, and type of spray depends on exactly what is being treated. Michigan law requires that commercial pesticide applicators inform the customer of what specific pest or disease the treatment is targeting.
2. The damage or potential damage to the tree must be sufficient to warrant spraying of toxic chemicals. If the problem is more cosmetic or nuisance, then an informed decision should be made as to whether spraying is warranted.
3. The timing should be right. The life cycle of most pests and diseases give only a small window of opportunity for spray control Spraying at other times is not effective and could actually worsen the problem (see Cottony Maple Scale on scale treatment page). A reputable spray company will inform the consumer if the treatment window has passed, as it often has when homeowners call. Unfortunately, many "spray sellers" do not even know the life cycle of common pests and diseases and are not motivated to tell the consumer that sprays are not needed or would not be beneficial.
There are some diseases that require a series of sprays for control. When that is the case, timing is critical for each application in the series. Many spraying companies time their "treatments" by the calendar and not by the life cycle of the organism to be controlled. They apply combinations of products in a shotgun, "one size fits all" approach that is not scientifically sound and can cause as many problems as it is intended to treat.
The "spray sellers" often say that theirs is a "preventive" approach, suggesting that applying an insecticide and a fungicide and maybe a miticide several times will prevent any problems that could arise. That is akin to a doctor giving a patient pills for several different diseases and instructing them to take the pills regularly just in case the patient is prone to those diseases. The adverse effects would likely outweigh any potential beneficial effects.