used on fruit trees and many woody ornamentals. Insect

used on fruit trees and many woody ornamentals.

Insect and mite eggs must exchange oxygen with the atmosphere through their shells. The trick with an oil spray is to cover the plant with a layer of oil that will cut off oxygen to the eggs and kill them, then dissipate before it injures the plant. Modern oil sprays are highly refined and much less likely to injure plants than the old dormant sprays, but most will still advise against using if freezing weather is in the forecast.

There are many brands of oil sprays on the market, and most no longer use the term ‘dormant’ in their trade names. Many are referred to as horticultural oils, and most will have dormant as well as growing season uses on the label.

At this time of year, most over wintering eggs are very dormant, and the exchange of oxygen is quite slow. It is possible to make an application of oil that covers the eggs, but dissipates before it has a chance to kill the egg. In the warm days of early spring, the exchange is much faster as the eggs prepare to hatch, and oils are more effective. Although the label will say to spray just before bud break, there will be no damage to the plant if a few buds are showing a little green. If warm weather has induced any eggs to hatch, they will be killed on contact by the oil.

It is important to remember that oils are only one tool in controlling pests on fruit trees and ornamentals. They have no effect on diseases, or insects that migrate to the plants later in the season.

Virginia Cooperative Extension programs are open to all, regardless of race, color, religion, sex, age, veteran status, national origin, disability, or political affiliation.

Chuck Hoysa is the Extension Agent, Horticulture for PD 9 and is located at 24 Pelham Street in Warrenton. You may reach Chuck at crhoysa @vt. edu