McCreary: Time for dormant sprays on fruit and nut trees

<p>[Celebrating seasonal holidays usually pulls us away from routine garden maintenance, often happily so, but as it happens winter holidays happen to coincide with a spray schedule for dormant fruit and nut trees. Their dates are a convenient reminder to stay on track in the garden.</p><p>For many years, I’ve been guided by the reminder to apply the first in a series of sprays before sitting down to Thanksgiving dinner or at least by the first of December. New Year’s and Valentine’s Day signal later applications, especially if trees have had a bad case of peach leaf curl, mites, scale, or aphids.</p><p>Spray oils sold to home gardeners are formulated for use in all seasons. They often are marked with a descriptive label such as narrow-range or supreme to indicate that they do not damage foliage. Most are petroleum based, but some such as neem oil are derived from plants.</p><p>Spraying in winter while trees are dormant is important because oils can reach into recesses in the bark on leafless trees and smother mites, various insects, and their eggs. If pests or eggs are not present, however, there’s no reason to spray.</p><p>Oil can be mixed with lime sulfur for dormant sprays, which help control fungal diseases, mites and some insects, but this mixture should never be applied during the growing season when it will seriously damage foliage.</p><p>Note also, that apricots should never be sprayed with sulfur, which will compromise fruiting, but only with fixed copper sprays or oils.</p><p>For best protection against leaf curl on peaches and nectarines, use either a fixed copper and oil spray or Bordeaux mixture, a blend of copper sulfate and lime that combats both fungal and bacterial diseases. Both sprays are effective against peach leaf curl, leaf spots, apple scab and shot hole fungus.</p><p>Where fire blight is a persistent problem on pears and apples, UC Davis horticulturists recommend spraying with a very weak Bordeaux mixture, less than one percent, when blossoms begin to open in spring and daytime temperatures are above 60°F. If humidity is high during bloom, repeat applications every 4 or 5 days throughout the bloom period.</p><p>Oils should never be sprayed on drought-stressed trees or during wet, foggy, or freezing weather. When applying any pesticide, always read label warnings and follow directions — it’s the law.</p><p>[SUBHEAD_RAG_]<IP0>Winter spraying</p><p><MC><BL@199,12,11,10>Apple and pear. Dormant oil controls scale, overwintering aphid and mite eggs, and pear psylla. Other pest problems need attention in later months. Remove any blackened wood damaged by fire blight and spray with copper.</p><p></BL><BL@199,12,11,10>Apricot. Dormant oil spray controls scale, mite and aphid eggs, and the peach twig borer. Never use sulfur on apricots. Prune only in late summer to avoid Eutypa fungus from entering cut branches.</p><p></BL><BL@199,12,11,10>Cherry. Cherries are susceptible to oozing from gummosis (bacterial canker) and may respond to dormant sprays containing fixed copper.</p><p></BL><BL@199,12,11,10>Olive. After harvest, olives can be sprayed with a fixed copper solution to prevent peacock spot disease.</p><p></BL><BL@199,12,11,10>Peach and nectarine. These two very similar fruit trees require repeat applications of fixed copper spray to control peach leaf curl. Thanksgiving — or Dec. 1 — signals the first spray; Valentine’s Day — or Feb. 1 — signals a final spray. If leaves have not fallen, either strip the tree or spray while foliage is still on. In December or January, prune off half to two-thirds of last year’s growth to stimulate new fruiting wood and strong branching; spray the ground after cleaning up all leaves and branches. Use dormant oil if scale is present.</p><p></BL><BL@199,12,11,10>Plum and prune. Dormant oil spray controls scale and overwintering aphid and mite eggs; apply copper for shot hole fungus. Heavy pruning may be needed to control tree size and to remove damaged or dead wood. Spray the ground after pruning. </p><p></BL><BL@199,12,11,10>Nut trees. Remove any dried nuts still hanging on the tree or lying on the ground. Spray with dormant oil to control scale if needed. On almonds, oil sprays also help control peach twig borers and mite eggs. Avoid spraying oil on walnut trees when buds begin to break and dormancy ends.</p><p>There is no spray for controlling the walnut husk fly in home orchards. It helps to remove insect-damaged nuts as soon as you notice them. It also helps to place a tarp under the tree in July and August so that any maggots that hatch from fly eggs will not drop into the soil to pupate.</p><p></BL>[SUBHEAD_RAG_]<IP0>Resources</p><p><MC1>For a quick summary of year-round fruit tree maintenance, visit http://homeorchard.ucdavis.edu and click on calendars. You’ll find a chart written by Paul Vossen, Sonoma County UC Extension Farm Advisor.</p><p>For more in-depth data, purchase “The Home Orchard,” a UC ANR Publication (#3485) available at the UC Extension Office, 133 Aviation Blvd., Santa Rosa (565-2621) or online at http://anrcatalog.ucdavis.edu.</p><p>Rosemary McCreary, a Sonoma County gardener, gardening teacher and author, writes the weekly Homegrown column for The Press Democrat. Write to her at P.O. Box 910, Santa Rosa, 95402; or send fax to 664-9476.</p>