Timing for Spraying Dormant Oil

As apple trees go through the various stages of dormancy, insects go through stages of hibernation.  The thing is, these insects don't  breathe when in hibernation, or at least a very, very little.  Aphid, mite, and lepidoptera (moth) pests lower their respiration during late fall as the temps drop below 50 degrees and do not increase respiration enough until the temps start to hit 43 to 50 degrees in early spring. So they will not be breathing enough to get smothered by any oil sprays until early spring.. So save your sprays for early spring and stay warm during winter!

"Proper timing is critical when using dormant oil sprays. Dormant oils should be applied in late March or early April before the plants show signs of breaking dormancy (before “bud break”). Dormant oils applied in February or early March are not effective as insects are not actively respiring at this time and, therefore, are not vulnerable to the oil’s suffocating effects. Dormant oil sprays should be applied as close to bud break as possible."

So  when do I do my oil spray if not in winter?  Both daytime and nighttime temperatures should ideally be above 40°F when applying dormant oil and copper sprays to apple trees. Daytime temperatures should be above 40°F for effective application and absorption of the spray and nighttime temperatures should remain above freezing (32°F), but preferably above 40°F for at least 24 hours after application to prevent damage to the trees.

Here's the clencher: The ideal temperature range for applying these sprays is between 50°F and 70°F. It's crucial to avoid applying the spray if temperatures are forecast to drop below freezing within 24 hours after the application. I recommend waiting for a 24-hour period with temperatures consistently above freezing before applying the dormant oil and copper spray. An oil spray will be of no benefit if the temps are too low and the insects overwinter on tree bark are not sufficiently breathing to be smothered by the oil spray.

This publication contains pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registration, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author assumes no liability resulting from the use of these recommendations.