Dormant Spraying of Fruit Trees

During the winter months, the garden is put to bed. Catalogs of helpful gardening tips and direction, that once were studied daily, pile up as you shift gears and begin planning for the holidays. 

Sitting by the fire with a cup of hot tea, you reminisce of summer warmth and beauty. However, as the holidays begin to pass us, the thought of the dormant season presents itself as you notice the barren branches no longer possessing leaves or flowers. 

After the first leaves fall, yet not before the precious plant buds begin to break open in the spring, you recognize this is the best time to manage problems of pests and diseases from the previous season this past year. 

After the autumn leaves have presented their colorful show and fallen to the ground, it is time for the trees to begin their long winter nap. This time is important in removing diseased wood from the trees, fruit and leaves from the ground around the root base of the trees. Any fruit mummies, left on the tree must be removed as well. Leafless trees await your attention and allow you to prune for future success. 

Pruning aids in promoting open areas for sunlight and improved air circulation within the branches and canopy of the tree. 

Winter is the best time to apply dormant oil sprays for control of pests and to limit infection and the spread of certain diseases. 

Dormant oil sprays have a variety of names depending upon the manufacturer or desired outcome of use. These oils, horticultural oil, are also known as insecticidal oil, narrow range oil, supreme oil, superior oil, dormant oil or ultrafine oil can be used in ornamentals, fruit and nut trees. These oils are used to control soft bodied insects such as aphids, immature white flies, immature scales, psyllids, thrips and some insect eggs as well as mites.

Additionally, certain horticultural oils can help control leaf curl, shot hole fungus, powdery mildew and other fungi. Some oils have the ability to kill insects on direct contact. 

Thorough application and coverage is essential for successful treatment of problems. Horticulture oils are low in toxicity to wildlife and beneficial insects. Although it should be noted, care must be taken not to swallow, inhale or expose your skin and eyes. 

Wear protective gear and long sleeves and long pants when spraying! 

Dormant sprays may not be needed every year in a backyard orchard. The previous season will help you decide if the amount of disease and insect damage warrants spraying. 

Treat at the beginning of dormancy in late November and again just before the buds begin to open in February or early March. One way to remember when to consider dormant spraying is to do so around Thanksgiving time and Valentine’s Day. 

Three applications may be necessary depending on the pests and the weather. 

Once flower buds begin to open you may damage fruit and kill pollinating bees if spraying is done at this time. Therefore, it is important to spray at the proposed times before “bud break”. 

Pump sprayers are ideal ways to evenly apply the necessary material. Do not spray drought stressed trees, during rain or during or prior to freezing weather. Oils should be sprayed within 30 days before or after applications of sulfur or certain other fungicides had been applied to the trees. 

Fixed copper fungicides may be used for certain diseases and may take several applications to reap the desired result.

A partial listing follows for fruit trees: 

• Apple and pear - dormant oil helps control scale, overwintering aphids, mite eggs and pear phyla.
• Apricot - dormant oil helps control scale, mite and aphid eggs and peach tree borer. Never use sulfur on apricots.
• Cherry - is susceptible to oozing from gummosis (Bacterial canker) and may respond to dormant sprays containing fixed copper.
• Peach and nectarine - require repeated applications of fixed copper spray to control peach leaf curl. In December or January, prune off half to two thirds of last season’s growth to stimulate new fruiting wood. Spray the ground after removing leaves and branches. Use dormant oil if scale is present.
• Plum and prune -dormant oil helps control scale and overwintering aphid and mite eggs. Apply copper for shot hole fungus. Heavy pruning may be needed to help control tree size. Spray ground after clean up.
• Nut trees- remove any nuts still hanging on the tree. Spray with dormant oil to control scale. Oil sprays also help control peach tree borers and mite eggs. 

CAUTION- always check the label for targeted pests and directions of use.

An excellent reference book available at UCANR: The Home Orchard, 2nd Edition 

References 

“Winter Pest Management in Backyard Deciduous Fruit Trees” ANR Publication 8368 - July 2009 by Pamela M. Geisel, Academic Coordinator, UC Statewide MG Program and Donna C. Seaver, Program Representative, UC Statewide MG Program.