The new house came with two mature apple trees. Both were in desperate need of pruning, which they finally received this year. And as we found out last year, they were also in desperate need of dormant oil. Most of the apples had worms in them. (I somehow had the false belief [courtesy of my husband] that dormant oil controlled worms in apples. It doesn't.)
Determined not to lose the crop this year, I picked up some dormant oil at CAL Ranch a month or two ago. And at the same time I wondered what I’d do if I didn’t have dormant oil.
It never occurred to me that I might be able to make my own.
However, my inquisitive husband decided to read the label on the dormant oil bottle:
- Active ingredient: Mineral oil, 98%
- Emulsifier: 2%
Seriously, mineral oil? So I decided to do some research. After all, being able to protect apple and other fruit tree crops from bugs may become important.
Dormant oil refers to the season when the pesticide was traditionally applied—when the tree was dormant (which means the buds have not begun to swell yet). Now there are newer formulations that may be applied at different times throughout the year.
Commercially produced dormant oil is typically produced from refined petroleum products like mineral oil. The dormant oil is usually applied using a hose-end sprayer that will mix the dormant oil and water in the correct ratio for application. The dormant oil also contains an emulsifier so that the oil and water will mix and provide more complete coverage.
Dormant oil controls the following insects:
- Aphids
- Adelgids
- Caterpillar eggs
- Leafhoppers
- Mealybug
- Mites
- Scale
- Thrips
- Whiteflies
Again, dormant oil does not control codling moths.
Dormant oil is far more effective on young insects and much less effective on more mature insects, making timing and early treatment essential for best results.
It’s important to note that dormant oil needs to be applied when the conditions are right. Do not apply dormant oil when:
- It is sunny, because the oils can burn the leaves.
- Temperatures are freezing or close to freezing, because the emulsifiers don’t work as well and coverage will be uneven.
- A freezing trend is in the forecast within the next several days.
- Temperatures are expected to reach 90°F or more.
- Plants are stressed by drought.
- Conditions are humid—high humidity slows evaporation and can cause burning.
- Rain is in the forecast within the next 24 hours.
- Sulfur-based pest control has been used within the last 30 days.
Do apply dormant oil when temperatures are in the 40-70°F range, with temperatures expected to remain above 50°F for the next 24 hours. (Yeah, I’m not too sure how those of us in colder climates are supposed to pull this off, but that’s what the recommendation is.)
Dormant oil works to kill insects by suffocating them (the oil blocks the spiracles through which they breathe), disrupts the maturation of insect eggs, or interferes with the insects’ ability to eat, so they starve to death. Better them than me.
Of course, you can still buy dormant oil in stores. But you can also make your own that will be every bit as effective. Some are simple; others more complex. Most of the sites offering DIY recipes for dormant oil note how truly toxic petroleum based products are, and that mineral oil should never be used, yada, yada, yada. You’ll have to decide that one on your own. Do you want to go with perfectly good cooking oil that could be used for food? Or do you want to use mineral oil that isn’t food, that some people claim is toxic (but that the agricultural industry has used for decades)? Or do you want to do nothing and risk losing the fruit crop or having to eat wormy fruit? Also, while none of the resources I checked mentioned it, I believe this would be a great use for rancid cooking oil.
Recipes
Truly Dormant Oil Spray
1 cup vegetable oil
2 tablespoons liquid soap
1 gallon water
Combine everything, shake, and spray
Dormant Oil for Small Applications
1 cup vegetable or mineral oil
¼ cup dish soap or Murphy’s Wood Oil soap
Combine in a pint canning jar. This is your stock solution. Use 1 tablespoon per quart of water in a spray bottle. Do not use on hot and/or sunny days, as the oil may burn the leaves.
Other options (the directions are all the same—combine everything, shake well, and spray):
#1 (This one is good for killing those overwintering pests as well as controlling fungal diseases.)
2 tablespoons cooking oil
1 tablespoon baking soda
1 gallon water
#2 (This one also helps eliminate fungal spores and is a good option for spraying after pruning.)
2 tablespoons baking soda
5 tablespoons hydrogen peroxide
2 tablespoons castile soap (olive oil based)
1 gallon water
#3 All-Purpose (For killing soft-bodied insects like aphids, mealybugs, and mites, it works by smothering the insects, so be sure to spray generously.)
1 tablespoon canola oil
4 drops of dish detergent
1 quart water
After spraying, be sure to clean the sprayer out very well with warm water. Any oil that remains in the sprayer may harden and clog the mechanism.
As some of you more experienced gardeners know, dormant oil doesn’t actually protect apple trees from codling moths. That’s something I learned while writing and researching today. Now off to research what to do about those codling moths.
Links to related posts:
References:
https://thegoodearthgarden.com/effectively-use-dormant-oil/
https://farmhomestead.com/homemade-dormant-oil/
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/white-oil-insecticide.htm
https://www.hunker.com/12004024/homemade-dormant-oil-spray-for-fruit-trees
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