Get a head start on fruit tree problems with dormant oils


CORVALLIS – Just when you’re ready for a long winter nap, it’s time to take care of your fruit trees.

If you don’t, there’s a good chance they’ll struggle in the coming season. Paying attention to them now helps keep insects and disease away, said Steve Renquist, a horticulturalist for the Oregon State University Extension Service who has taught hundreds of gardeners the basics of fruit tree management.

Applying dormant sprays – premium oil, copper and sulfur – helps control pests and diseases like codling moth and apple scab.

Superior oil, also called horticultural oil, is a highly refined (up to 99.9 percent pure) miscible oil that, when mixed with water and sprayed on trees, will suffocate overwintering insects and their eggs. It targets mites, aphids, leafhoppers, mealybugs, leaf miners and more.

Sulfur is a fungicide that controls fungal diseases such as apple and pear scab and peach leaf curl.

Copper is a fungicide and bactericide that controls diseases such as fire blight, fire blight, and nectria canker. It kills bacteria and fungal spores left in trees, including Pseudomonas syringae, a common bacteria that can cause gum disease, which oozes honey-infested sap from the cracked bark. In a rotation of copper and sulfur, copper will treat bacteria and sulfur will best target fungal diseases.

With a spray regimen of all three – used in conjunction with good hygiene and pruning practices – most fruit tree problems can be nipped in the bud, according to Renquist.

The trio of pesticides, which can be used in organic gardens, fit perfectly into the field of integrated pest management or integrated pest management, a practice that uses a variety of low-risk tools to treat pest. pest problems and minimize risks to humans, animals and the environment.

“They are a very important part of a good IPM,” Renquist said. “When planning a program, you want to use products that are low in toxicity and that won’t cause a lot of environmental damage. Dormant sprays get good results. Their level of toxicity to animals is quite low if you follow the labels. Superior or horticultural oil kills target insects, but beneficial insects are rarely around trees during the dormant season.

A good reference for disease and pest control is Extension’s Disease and Insect Management in Home Orchards, which contains a list of cultural practices and products that are least toxic to various pests and diseases.

Renquist recommends a three-pronged approach to spraying. In the fall around Thanksgiving, apply copper. Spray sulfur in early January, then at least two weeks later spray dormant oil. Then do another copper spray from mid-February to the end of February. Do not combine copper and sulfur or sulfur and oil in the same tank to minimize the risk of damaging tree bark.

If you don’t like to spray or forget about spraying early, Renquist said the January application is the most important. This year, if you missed the January timing, you had better do the third spray.

Some tips from Renquist:

  • Read the labels of all the products you use and follow the directions. The incorrect use of any pesticide is not only harmful to you and the environment, it can actually cause damage to the very plants you are trying to benefit from.
  • Apply Superior or horticultural during the dormant season to allow for greater coverage and a greater likelihood of reaching the majority of insects.
  • Spray when temperatures are above freezing but before bud break.
  • Do not mix copper and sulfur in the same tank.
  • Prune trees to keep branches separate for good pesticide coverage and good hygiene. The best time is January for the last spray or two to cover pruning wounds.
  • Clean fruit, leaves and debris from under trees. They can harbor insects and disease. If you don’t want to rake the leaves, mow them a few times and let them decompose.
  • Remove weeds around the trunk and under the tree where insects and rodents can hide.
  • Add organic matter around trees for fertility and because increasing microbial populations in the soil will help devour leftover orchard spray that falls to the ground.
  • Accept some fruit damage.
  • When planting fruit trees, think about dwarfs so that you don’t need a ladder for spraying.

For more information on fruit trees see Extension’s Growing fruit trees and nuts in the vegetable garden and Training and pruning of your home orchard.

– Kym Pokorny, [email protected]

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