Actually, tis almost past the season, and I sprayed the trees a week and a half ago, but four baby chicks have distracted my attention away from writing about fruit trees. Fruit tree care is one of Kelly’s many areas of expertise (I attempted unsuccessfully to sweet-talk her into writing this post and picked her brain extensively). This was the first year that I donned a surgical mask and my rattiest pair of corduroys and braved the copper and horticultural oil.
There are a number of reasons to spray some fruit trees with copper and oil. While the copper acts as a general fungicide, helping to prevent everything from peach leaf curl, to brown rot, to rust, to fire blight, oil serves as a spreader-sticker that also kills overwintering insects like wooly apple aphids.
Spraying before the trees bloom is important because copper is toxic to bees and other pollinators, and horticultural oil will smother them. For some diseases, however, you will have to spray while the tree is in bloom. Fire blight and brown rot are both examples. In this case, it is best to time your spray to hours of the day when foraging insects are most likely to have returned home.
As someone who had never sprayed anything other than fish emulsion before, I can assure you that I found the prospect somewhat daunting and that I only agreed to it because Kelly was out of town and I was afraid the flowers would open before she returned. As a newly minted “veteran sprayer,” I can say that it wasn’t all that bad, and I’ll even go out on a limb and say that anyone can do it. In that spirit, allow me to explain the process.
Trees to spray
Not every fruit tree should be sprayed with copper and horticultural oil, and trees that may benefit from spraying in one climate, don’t need to be sprayed in others. Persimmons, pomegranates, mulberries, and citrus are examples of trees that, at least in our San Francisco Bay Area climate, don’t need to be sprayed with copper and horticultural oil.
That being said, peaches, nectarines, plums, grapes, pears, and apples can all benefit from a dormant spray to help fight off fungal infections carried by the rain and overwintering insects.
Keep in mind that, although copper is used by organic growers, it is a heavy metal and will ultimately end up in your soil. Toxic build-ups are possible over time.
Spraying the trees
Spray on a dry day when the copper won’t be washed off by rain or diluted by fog for at least a few hours (a few days is preferable).
Mix up the liquid copper and horticultural oil in the sprayer, making sure to follow the directions carefully for both. In my case, Kelly’s horticultural oil and 27.15% copper solution called for 3 tablespoons of oil and four tablespoons of copper per gallon of water.
I used a Gilmour hose-end sprayer, available at many nurseries and hardware stores. The sprayer attaches to the end of a garden hose and mixes the water with the copper and oil solution.
Kelly’s sprayer has eight settings. The higher the number on the dial the more tablespoons of copper and oil are added per gallon of water. I used 8 tablespoons per gallon on the peach and nectarine trees and four tablespoons per gallon on the pear trees.
While dormant spraying is easy enough to do yourself, it’s worth exercising caution. Contact your local extension office and try to find knowledgeable nursery-folk to make certain that you are using the proper proportions and only spraying trees that really need it. Every time I visit the local hardware store, I am shocked and horrified at the number of chemicals available to anyone who feels like paying the price.
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