Dormant Spraying, Pruning Fruit Trees
March 3, 2014
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While much of the eastern U.S. has been bundled up, Utah has experienced one of the warmest Februaries on record. But as many of you who have lived here much of your lives, wait 5 minutes and the weather will change.
In other words, don’t get too hasty with applying a dormant spray or pruning your peaches or apricots. A dormant spray of horticultural oil (and sometimes oil plus insecticide) is an excellent management tool for a variety of fruit tree pests, including aphids, peach twig borer, scale, and blister mites.
There is an optimal window in which to apply your dormant spray that will provide the best results. If you spray too early, it will have little effect on these pests, and if you spray too late, you may damage fruits or flowers.
When insects are still dormant (in “diapause”), they are not susceptible to treatment because they are not actively metabolizing or respiring. The insects that we are targeting start to become active at the same time that trees start exiting dormancy: when sap flows and buds start to swell. For this reason, we call this early spring treatment a delayed-dormant spray because it is not technically applied when trees are dormant.
The optimal window for applying the delayed-dormant spray will depend on the bud stage of the trees in your own backyard or orchard. The spray can be applied during the following range of bud stages:
Keep in mind that dormant sprays are not required every year. For example if you had an aphid or peach twig borer problem last season on your peaches, then apply your delayed-dormant spray this spring. If you have had very little damage from those pests, then you could consider skipping the spray.
When applying the delayed-dormant treatment, cover the tree thoroughly until they are dripping to get good application in all the cracks and crevices. If you are using horticultural oil alone, use a rate of 2% (mixed in water) for best results. For situations where aphids have been real problems in the past, consider adding an insecticide (such as malathion, carbaryl, acetamiprid, etc.) to the oil.
The next advisory will go into further detail on what insects are targeted by the delayed-dormant treatment.
Pruning Fruit Trees
Annual pruning of fruit trees helps to maintain vigor, tree health, and fruit size. Apple trees can be pruned almost any time in winter, but peach/nectarine, apricot, and plum trees should be pruned in spring, just before bloom. These trees are more sensitive to colder temperatures, and if they are pruned too early, they may experience some dieback.
When pruning any tree, never remove more than 1/3 of the canopy. In general, remove:
• rubbing branches
Also, head back over-long branches that have no side-branching to encourage lateral growth. Branches that are growing upward should be cut back to lateral twigs to maintain a manageable tree height.
When pruning large limbs, be sure to make a proper cut. Do not cut flush to the tree, but rather, angle the cut just outside the branch collar (the swollen area at which the limb meets the tree). Cutting into the branch collar prevents proper wound healing.
For peaches/nectarines, the majority of fruiting occurs laterally on long branches, with some on short branches. For cherries, apricot, and plum, most fruiting occurs laterally on short branches or spurs, with some on long branches.
Most cherries and plums are trained to the central leader system, while peaches/nectarines can be trained to the central leader or “open center” position.
Keep in mind, however, that in the open center system, the leader is removed, and scaffold branches form the bulk of the tree. For backyard trees, it is important to prevent heavy fruiting that may break limbs.
The majority of fruiting occurs on terminals of short branches or spurs. These trees can be trained to:
• central leader
For more information on pruning the orchard, see the USU Fact Sheet.
Precautionary Statement: Utah State University Extension and its employees are not responsible for the use, misuse, or damage caused by application or misapplication of products or information mentioned in this document. All pesticides are labeled with ingredients, instructions, and risks. The pesticide applicator is legally responsible for proper use. USU makes no endorsement of the products listed herein.