Dormant sprays: What they do and when to apply them

SALT LAKE CITY — Fruit trees, along with some other plants, can benefit from something called a delayed dormant spray. Dormant sprays are a type of horticultural oil used on fruit trees to help control various pests at different times of the year.

 

When to apply dormant spray

It’s still too early, said KSL Greenhouse Host Taun Beddes, but you need to keep an eye on the tree’s bud stages.

“You do this as the weather is starting to warm up [and] you’re seeing the trees’ buds expand. When this is happening, insect pests and things like spider mites are also breaking dormancy. And when you spray this really light oil on your tree, it smothers certain diseases, insect pests, and spider mites to make it so that it’s easier to control pests through the summer.”

Beddes said it doesn’t hurt to wait to do this because then there will be more insects that will be breaking dormancy.

“But if you spray when a tree’s in blossom, you will scorch the blossoms off the tree. So you’re timing’s going to be critical.”

For images of all the bud stages, refer to the Utah Home Orchard Pest Management Guide.

How much of a difference does it make?

According to Beddes, applying dormant spray is a common practice in commercial orchards because it ensures their fruit trees are kept pest-free. He said anything that overwinters on the fruit tree can be controlled with a dormant spray.

For example, although peach trees don’t usually get worms in the fruit, applying a dormant spray could help as they could still get green peach aphids or other pests.

Despite how effective they are, dormant sprays don’t prevent all insects. If the insect doesn’t overwinter directly on the surface of the tree, then a dormant spray won’t work on that particular insect, Beddes said.

Take the codling moth, for example.

“Because they overwinter in apples on the tree or in the ground, and they’re not on the bark usually, and there’s multiple generations through the summer, dormant oils won’t do anything,” Beddes said.

What’s with all the pests?

According to Beddes, there were only two generations of codling moth 30 or 40 years ago. Now there are three generations, which means there’s been a general increase in pests.

“Even things like aphids, they may have [the] opportunity to have more generations per year. We’re not getting as cold, and so the cold itself isn’t doing any damage to them as far as killing them. And so with warmer temperatures, you often see an increase in pests that will get your fruit trees.”

If you want fresh fruit but don’t want to purchase chemicals or deal with pests, Beddes suggested buying from a local orchard instead.

“We have orchards in every county, especially Box Elder and Utah County, but you can find local fruit stands with local fruit starting in mid-July.”

Read more from the KSL Greenhouse show:

• UDAF offering grants to help create a more pollinator-friendly environment
• Container gardening: A space-efficient way to grow
• Planning on starting seeds this spring? You’ll need these 3 things

KSL Greenhouse is live Saturdays from 8 a.m. to 11 a.m. Follow the show on Facebook, Instagram, and YouTube. You can also find more gardening info on our linktr.ee.