As the almond harvest ramps up, some California growers are encountering problems with nut removal this year, partly due to drought-related irrigation issues and partly because of high humidity during hull split.
“There have been a lot of reports of poor removal of Nonpareil almonds,” said David Doll, a University of California (UC) pomology farm advisor in Merced County.
Doll said that variety, an industry mainstay, is particularly susceptible to hull rot, which can increase the number of what are called “stick-tights.”
He said poor removal can also be caused by uneven ripening, boron toxicity and lack of irrigation.
Information on managing those issues is available on the following websites:
http://thealmonddoctor.com/2014/07/12/hull-sampling-for-boron/ for boron toxicity.
http://thealmonddoctor.com/2015/07/01/pressure_chamber_almond_irrigation/ on using a pressure chamber to schedule irrigation in almonds.
While boron is a micronutrient for almonds and is required in the process of flower fertilization and deficiencies can lead to a reduced set, too much of it is not a good thing. It is toxic if it’s too highly concentrated.
UC’s Franz Niederholzer, farm advisor on orchard systems, points out that boron toxicity results in gummy nuts that may form stick-tights.
Doll said growers at a loss for surface water have relied more on groundwater which is more likely to contain higher levels of boron.
Niederholzer says hull sampling should be done to determine if an orchard is deficient in boron or if it’s showing toxicity from boron. Hulls accumulate the nutrient, he says, but leaf values are not effective in determining levels.
Doll said boron toxicity is becoming “a bit more common” with the expansion of trees onto lower quality land or irrigation with low quality water.
The gummy deposits that form at wounds or other plant openings may be light brown to clear, he says.
According to Doll, soils and water with boron levels over 0.5 mg/l are at risk.
Uneven ripening also figured into the problems in nut removal this year.
“There was a protracted long bloom and a long period of ripening,” Doll said. “The nuts were not ripening at the same time.”
He says growers shook trees for harvest early in order to avoid problems with Navel orangeworm. Doing so meant some nuts that were not fully ripe and adhered to the trees.
Doll said vigorous growing conditions can also delay ripening. Again, it’s a matter of too much of a good thing - more than adequate water and the use of nitrogen throughout the entire growing season.
“Often, this is observed in younger orchards as they are being ‘pushed’ along with increased water and nutrients,” Doll said.
“Not much can be done about the long bloom period, but properly timed irrigation and nitrogen applications in the spring (especially early spring) can help reduce excessive vigor.”
The hull rot challenges this year may be pegged to higher humidity in June and July in parts of the state and rare record-setting measureable rain in Fresno County and elsewhere.
“Once a hull is infected by Rhizopus or Monilinia, a toxin is secreted which leads to the death of fruit wood,” Doll said. “As this toxin kills tissues, it can cause them to gum - especially at the peduncle, effectively gluing the nuts to the spur.”
He said hull stick-tights can form when severe deficit irrigation is applied between hull split and harvest.
His advice to growers - “If possible, try and reduce severe stress as this will increase the occurrence of stick-tights.”
Doll recommends using a pressure chamber to determine the stress level on trees, taking note that the more negative the number on the reading taken, the greater the stress level.
“If utilizing regulated deficit irrigation, tree stress levels should be kept at less than -15 bars, if possible,” he said.