Understanding Almond Set And Nut Drop
April 19, 2016 Questions about nut set are common for David Doll, University of California Orchard Nut Crop Farm Advisor.
In a recent blog post, Doll says anywhere from 15% to 40% of flowers on trees will actually set a nut, with most trees falling in the 20% to 30% nut set range.
A number of factors contribute to nut set percentage, including tree health, temperature, and flower density. Doll adds that spur density is a major contributor to flower setting ability. He cites research by Sergio Tombesi and colleagues that found fruiting spurs, if they’re given ample light, tend to be alternate bearing.
“These spurs may flower the year after cropping, but rarely set a nut. This is believed to be due to carbohydrate and nutrient depletion within the spur,” Doll writes.
The research also found spurs that double or triple crop will die. That means trees with a higher nut set percentage actually end up depleting the spur pool, which results a diminished nut set the next year.
Growers can play a key role in helping trees develop and maintain spurs. Practices such as proper irrigation, nutrition, and keeping potassium levels maintained can reduce spur death, according to Doll.
Weather also plays an important role in nut set. The ideal temperature range for pollen tube germination is between 50°F and 70°F. Colder or hotter temperatures can negatively impact development and decrease nut set.
Nut Drop Considerations
Doll also points to the three periods of nut drop as an important factor impacting nut set. After bloom, defective flowers will fall from the tree. About a month after bloom, another nut drop occurs, where pea-sized flowers that were likely never pollinated fall, as do some larger nuts that might not have been fertilized. Approximately 6 to 7 weeks post-bloom, some fertilized nuts drop due to resource competition, he explains.
The full blog post, including a figure describing fruit set in detail among various varieties, is available on the Almond Doctor’s website.
Subscribe Today For
