Although spring begins the third week in March, now is the time to begin taking care of spring insect and disease problems.
It is time to spray dormant oil on shade and fruit trees to kill overwintering soft-bodied insects and pests, such as aphids, scales, leafhoppers, and spider mites. Your trees will drip less sticky "honeydew" on your patio, car, and yard when you kill the eggs and overwintering adults of aphids. If your trees had disease problems last year, such as peach leaf curl or shot-hole fungus, add an appropriate fungicide to the dormant oil. The oil smothers the insects, while the fungicide kills disease spores.
Be careful when using oils, and when combining fungicides with horticulture oils, be very careful to follow the label directions. Some oils must not be combined with sulfur sprays for disease management, while others are formulated to be combined with certain sulfur sprays. In all cases, avoid repeated applications within a short interval.
To avoid damage to plants, temperatures must be above 40 F and below 85 F. Some trees are sensitive to these products, even when they are applied at the right temperatures. Never apply oils to blue spruce, blue junipers, or other blue evergreens, because the oil will turn the blue to green. The blue color will not return to the sprayed parts, but new growth may come in blue. Besides blue conifers, beech, Douglas fir, Norway spruce, redbud, white spruce, hickory, and red, Japanese, and silver maples are all sensitive to dormant oils. New growth can be damaged or killed if horticulture oil is used too late in the spring.
There are benefits to using horticulture oils on appropriate trees. They do little damage to the natural enemies of your target pests, because they degrade rapidly in the environment. Spraying in winter reduces the need for insecticide applications later. Treating roses with dormant disease control can reduce spring dieback due to "black" canker.
Always read and follow all label directions. Apply dormant oils in early spring before buds begin to swell with spring growth.
I will be presenting a free workshop, "Spring Pruning," 5:30-7 p.m., Feb. 9, at the Carson City office of University of Nevada Cooperative Extension, 2621 Northgate, Suite 12. If you would like to grow vegetables, but do not have room or need assistance to do so, join us for an organizational meeting of the Carson City Community Garden, 6-8 p.m., Feb. 13, at the Cooperative Extension office.
Contact me at 887-2252 or skellyj@unce.unr.edu, or your local University of Nevada Cooperative Extension office, if you have questions or need more gardening information. Or, check out many useful horticulture publications at www.unce.unr.edu. "Ask a Master Gardener" by e-mailing mastergardeners@unce.unr.edu
n JoAnne Skelly is the Carson City / Storey County Extension Educator for University of Nevada Cooperative Extension.
