Winter doesn't seem like a good time for insect control in your home orchard or landscape, does it? The frigid temperatures of February aren't conducive to much insect activity. However, right now insects are hiding out on your trees and shrubs waiting for the warm temperatures of spring to pop out and mess with your plants.
One type of insecticide we can apply this time of year is horticultural oils. These are refined petroleum oils, and sometimes natural plant oils, combined with an emulsifying agent.
Horticultural oils are fairly safe and non-toxic to humans, and don't have some of the health risks of other synthetic insecticides.
When applied, these oils spread across plant branches, in and among the nooks and crannies of bark, to kill soft-bodied insects, such as scale, aphids and mites, as well as some eggs.
Horticultural oils can kill pests in different ways. The most common is by asphyxiation. The oil clogs up an insect's breathing holes, or spiracles, and blocks respiration.
In other insects, oils act as a metabolism inhibitor by interacting with fatty acids.
They can also interrupt the way certain insects, like aphids, feed and transmit plant viruses.
In the past, thicker oils, often called dormant oils, were recommended for use in winter.
Dormant oils were too heavy to use on plants during the warmer months because they caused harm to leaves and fruit. As oil technology has advanced, improved oils are available that can be used year-round. In fact, most oils on the market today don't have any temperature restrictions.
The best time to apply an oil spray would be on a warm winter afternoon. Any insects hanging out on the tree branches, such as scale or aphids, will be actively respiring. This will allow the oils to work more effectively.
Applying oil twice during the dormant season is recommended. I would suggest spraying once in February, and if possible, spray again just before bud break on fruit trees.
Make sure to focus on ample coverage, especially in branch crotches and branch tips.
When searching for a horticultural oil at a garden center or hardware store, I recommend purchasing an all-season oil, in case you need to use it during the summer. For example, commonly available brands like Hi-Yield and Bonide produce all-season oils that are labeled for several plant species.
Apples, pears, blueberries, grapes, peaches, plums, figs and countless ornamental plants can benefit from an oil application.