WHAT ABOUT "DORMANT OIL" SPRAYS?
We are often asked about dormant oil sprays. They are still routinely applied by many companies and can be beneficial in some cases. We have largely abandoned the use of oil sprays for a number of reasons:
1. Dormant oil sprays are promoted as a less toxic alternative to the use of insecticides and miticides. In fact, they are less likely to harm beneficial insects and if applied properly, with correct timing and technique can help to control scale insects and possibly cool season mites. They may also be effective for some adelgids. Our experience has been that even with good equipment and good technique, control has been limited and disappointing to us and our customers.
2. Oils work by "smothering" the insects or mites. In order for this to happen, a continuous layer of oil must be applied to all the plant tissues and must persist for long enough to kill the pest. The optimal conditions for this to happen include a specific temperature range at the time of application, correct humidity conditions and the timing has to be right to contact the pest during a vulnerable stage of its life cycle.
3. Oils can cause damage to some evergreens and some tissues and young foliage on deciduous trees. In many cases, this damage is worse than the damage of the pest being treated.
4. Oils can damage surfaces of houses, lawn furniture, vehicles, swing sets, etc. and it is difficult to keep the spray off of those surfaces when spraying even smaller trees.
5. It is virtually impossible to get adequate coverage of large trees for oils to work, even with excellent equipment and experienced applicators.
We have found that we can achieve excellent control of soft scale insects on very large trees with trunk injection of insecticides. There is long term control, no adverse effects on beneficial insects, and no environmental toxicity.
Mites can be treated with specific miticides. Adelgids can be treated with systemic, soil injected or drenched insecticides that have very low toxicity and do not damage surfaces or healthy foliage.