Dormant horticultural oil applications to trees and woody ornamentals can be very useful to help control insect and disease problems.
The treatment can be done once or twice a year during the dormant seasons in early spring and late fall. We try to do our first spring treatment in March, when we know the weather will stay above freezing overnight for at least 2 nights. We often do dormant oil applications in conjunction with dormant fungicide (copper) sprays to prevent fungal leaf diseases. Horticultural oil helps spread the copper fungicide which, in turn, can reduce the pathogenic fungi that overwinters on the bark, leaf scales and unopened buds. For trees that are disease prone, or in wet weather conditions, additional spray applications with an approved fungicide will need to be done in the spring after the tree begins to leaf out.
For the same reason, dormant oil applications work very well to control many overwintering insect pests, especially scale insects and mites. Dormant oils either suffocate, by blocking the breathing pores (spiracles), or penetrate and destroy cells of exposed insects or mites. Since insects’ exoskeletons (bodies) are composed primarily of chitin, a type of hardened wax, the oil can actually dissolve the wax coating and kill the insect or cause it to suffocate. For this reason, it is also effective against overwintering eggs and overwintering female insects. Oils are contact materials with minimal residual activity once the material has dried. Later, during the season, foliar applications with other materials may need to be scheduled for a complete management program.
Horticultural oil can also be used throughout the growing, or “verdant” season, to provide a reduced risk (so-called “organic”) management program for many insects. Often it is used in conjunction with insecticidal soap to provide a double whammy for excellent control. In extreme outbreaks, horticultural oil can be used with residual pesticides to act as a synergist and provide better control to knock down populations.
The material is a very finely refined oil product, with practically no odor, which acts to suffocate the “over wintering” target pest. It is by far one of the safest products used in pest management.
Please contact Fox Tree to set up an early spring treatment at your property and avoid insect problems later. If you have any questions, don’t hesitate to call us!