Have you begun your spring insect and disease control?
The optimum time to manage most insect and disease pests is often before the buds start to open and show spring color. They will be opening any day now, but until then, 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. When combining fungicides with horticulture oils, be extra 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 degrees and below 85 degrees.
Some trees are sensitive to these products, even when they are applied correctly and conditions are right. Never apply oils to blue spruce, blue junipers or other blue evergreens, because the oil will turn the blue parts green. The blue color will not return on sprayed parts, although 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 sensitive to dormant oils. In addition, new growth on any plant can be damaged or killed if horticulture oil is used too late in the spring.
There are many benefits to using horticulture oils. They do little damage to natural enemies of target pests because oils 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 late winter to early spring before buds begin to swell with spring growth. Later, if problem pests continue, shift from using dormant oil to using summer-weight oils.
Join me, 6-7:30 p.m. March 14, in our Carson City classroom at University of Nevada Cooperative Extension, 2621 Northgate, Suite 12, for a free workshop, "Water Efficient Landscaping - Saving Water and Work."
• JoAnne Skelly is the Carson City/Storey County Extension Educator for University of Nevada Cooperative Extension.