A gardener's work is never done, nor would we want it to be. Those who love their landscapes, plants and vegetable gardens strive all year to create the best growing conditions for their shrubs, trees, flowers, lawns and crops. With all this nice weather, I'm sure many gardeners are spraying dormant oils for insect and disease control.
If you had sticky goo dripping from your trees last year or bugs all over your roses, your plants were likely infested with aphids. A good time to control these messy pests is during plant dormancy. Try horticulture oil, called a dormant oil, in winter. Horticulture oils control aphids, scale and mite pests, in addition to a few other insects. Oils interfere with a pest's ability to breath, basically smothering it. They may also disrupt how an insect feeds. They pose few risks to humans, pets or beneficial insects due to their limited and short-lived residue. Some horticulture oils target disease organisms rather than insect. Some work against both.
Horticulture oils are refined petroleum products. Oils can injure some plants, so it is important to know what kind of plant you want to spray as well as what insect or disease you are trying to control. Blue spruce, blue junipers and other blue plants can lose their blue color when treated with oils. Read the label to see if your plant is on the sensitive list. Some sensitive plants are junipers, cedars, spruce " blue and dwarf Alberta are very susceptible " redbud, maples, particularly Japanese and red maple, and smoke trees. However, oils can work very well on most fruit trees and many other shade trees.
Spray dormant horticulture oils before the buds swell or color begins to show. Oils should not be applied when the temperatures are below freezing because freezing temperatures can cause the oil emulsion to break down and cover unevenly. Plants under stress may be damaged, so irrigate plants at least 24 hours prior to spraying or spray after a rain. Don't spray if rain or snow are likely to wash off your oil.
Often horticulture oils have been adapted to both winter and summer use depending on the concentration. Be sure to follow label directions. Explore a nursery's product section and read different labels to find the perfect horticulture oil for your yard.
For information, contact me, (775) 887-2252 or skellyj@unce.unr.edu, your local University of Nevada Cooperative Extension office or at www.unce.unr.edu. "Ask a Master Gardener" at mastergardeners@unce.unr.edu
n JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension.
