Written by Lynn Long, Extension Horticulturist, Oregan State University
Dr. Greg Lang of Michigan State University has found that late summer or autumn urea sprays increased the shoot hardiness of the cherries that he tested and produced up to 20% larger spur leaves in the spring. As a whole, throughout the growing season, the spur leaves are the most important leaves for supplying nutrients to developing fruit. Greg speculates that if the spur leaves are larger, than photosynthesis is increased and there are more carbohydrates being exported to the developing fruit.
In his trials, Greg applied two applications of low biurate urea as a foliar spray. An application on August 31 and a second application about one week later actually gave the best uptake of N into spur tissues and provided earlier acquisition of cold hardiness in the year that it was treated. However, application can be made up to leaf fall.
Each application should consist of 15 to 20 pounds of N/acre. In the past I stated that this was 15 to 20 pounds of actual N/acre, however, Greg actually used 15-20 pounds of urea product per acre. Local growers have used both rates, but those that used the higher rate have commented that they saw good effect and no phytotoxicity. I would encourage you to use the rate that you are most comfortable with.
In Greg’s trials he mentioned that dilute sprays of 250 gallons/acre are possible, but some leaf burn at the leaf margin could be possible with these dilute sprays. Concentrated sprays ranging from 25 to 75 gallons/acre showed less phytotoxicity when applied with a curtain-type sprayer (small volume, small droplet size). The reduced toxicity which was noted with the concentrated sprays is probably due to less pooling of the material along leaf margins and therefore less burning of the foliage.
Dr. Ashley Thompson
Fruit Tree Extension, Wasco & Hood River Counties
Oregon State University
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