Garden Detective

When to spray fruit trees? It depends

Thrips are tiny insects, usually 1/20th inch long. Shown here is the onion thrips (Thrips tabaci), left, and the slightly larger western flower thrips (Frankliniella occidentalis).
Thrips are tiny insects, usually 1/20th inch long. Shown here is the onion thrips (Thrips tabaci), left, and the slightly larger western flower thrips (Frankliniella occidentalis).

Experts tackle readers’ garden questions.

Q: I had a helluva time with thrips in 2017, but I also did not know what they were at the time and did not spray for them either – other than my typical two- to three-time dormant spray with copper and horticultural oil. I live in San Jose and have around 35 fruit trees in my backyard orchard: cherries, peaches, apricots, pluots, apples, pears, guavas, pomegranates and citrus. I covered my backyard with weed fabric last year and it has a 3- to 4-inch layer of mulch, so virtually all of the weeds have been kept at bay (knock on wood). I can already see that several peach trees have swollen buds and bloom should start in a week or less.

I purchased this organic 3-in-1 spray made by a company called Organic Laboratories Inc. and plan to use it; the spray is also a fungicide. The question is when to spray! From what I’ve read, it sounds like I should spray at 10 percent bloom, maybe 50 percent bloom, and 90-plus percent bloom, and then after June drop. What are your recommendations? Is that too much spraying? From what I’ve read, it sounds like spraying at bloom is the most important time!

Can all my fruit trees be sprayed, including cherries and citrus, or is this really a peach and apricot problem?

Mike McGee, San Jose

Bee garden writer Debbie Arrington: First, are you sure it was thrips?

“Thrips usually aren’t a big problem except for nectarines, on which they cause russetting,” said Chuck Ingels, farm adviser for the UC Cooperative Extension in Sacramento County.

Thrips are itty-bitty insects (less than 1/20th of an inch long) with narrow bodies and long, thin fringed wings. They range in color from translucent white to black. They damage plants by puncturing the outer layer of cells, then sucking out the contents.

“Did he sample for and find the insects, or is he just going by symptoms?” Ingels said. “If they’re on all his fruit trees, it’s probably something else.”

Thrips also are a common pest on roses, particularly light-colored varieties. But there are an estimated 6,000 species of thrips with specific preferences for what they like to eat, from avocado to toyon.

The problem with spraying for thrips is that honeybees can be collateral damage. Bees are needed to pollinate your fruit trees. Some thrips also eat bad bugs and are actually a good insect.

“A bloom-time spray of spinosad is best; follow the label closely and ensure good spray coverage,” Ingels said. “It is most effective when sprayed twice, a week apart. I usually try to time it for early-mid bloom and petal fall, but it is essential to not spray during the period when bees are flying, since it kills bees – even though most formulations are organic. Spray early morning or late afternoon only, or just wait for the second application until the very tail end of bloom.

“No other timings will control thrips,” Ingels added, “and unless it has been a pest in the past, there is probably no need to control it. These and other thrips species are actually beneficial in that they kill spider mites and other pests. But of course, as a nectarine pest, they’re often devastating!”

For more on thrips and how to control them, see Pest Note 7429, “Thrips,” on the UC integrate pest management website,

The Bee’s Debbie Arrington is a consulting rosarian and lifelong gardener;, @debarrington, 916-321-1075.

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