In some cases, we saw better control with soybean oil and less phytotoxicity for some plant species. The spray mix consists of water, an emulsifier, and soybean oil. The researchers spray two to three gallons of the mixture on each tree. When the spray mixture is made with larger amounts of soybean oil, it's very effective at delaying bloom and thinning fruit in peach trees. Both impacts are useful to fruit growers, who often seek to delay bud development on trees to escape early season frosts.
Some buds die in the process, which thins the upcoming crop, bringing it to a manageable level.
The soybean spray thins fruit on trees more cost-effectively than hand thinning. While most of the research has been with peach trees, Deyton says the soybean oil-based spray could also work on apple trees.