Winter orchard care: Spray horticultural oils, fungicides soon

Oregon State University Extension Service is advising growers to start winter preventative plant health applications in orchards soon.

OSU assistant professor Ashely Thompson says winter dormant spray programs – which typically include horticultural oils as well as copper and sulfur fungicides – should kick off around the Thanksgiving holiday and continue through mid-to-late February.

“You want to use products that have low toxicity and won’t cause a lot of problems for the environment, and dormant sprays score pretty well,” said Thompson. “The toxicity level for animals is pretty low if you follow the labels. Horticultural oil kills target insects, but beneficial insects are rarely around trees in the dormant season.”

Specifically, dormant spray programs target mites, aphids, leafhoppers, mealy bugs and coddling moths, as well as diseases like apple and pear scab, peach leaf curl, bacterial blight and fire blight, she said.

Thompson recommends the following spray program for orchard trees:

• Apply copper around Thanksgiving to knock back bacteria and fungal spores.
• Spray sulfur in early January and then spray horticultural oil two weeks later to affect overwintering bugs.
• Make your second application of copper fungicide in mid-to-late February before buds begin to open.

The researcher also says do not mix copper and sulfur in the same tank, and do not mix sulfur and horticultural oil. If you miss the Thanksgiving application, you should still spray sulfur in January and copper in February.

Additional winter fruit tree care tips from Thompson:

• Read and follow all pesticide labels.
• Spray when temperatures are above freezing and before buds break.
• Apply horticultural oil only during dormancy for the best coverage.
• Prune in January so late winter sprays also cover pruning wounds.
• Clean up fruit, leaves, weeds and debris under trees where codling moth and other insects overwinter.
• Prune out diseased wood.
• Add organic matter around trees for fertility but keep mulch away from the trunk.
• Accept a little fruit damage rather than relying on higher-toxicity products.
• Consider dwarf trees so spraying can be done safely from the ground.