A high-quality California almond crop is a year-round process which can increase grower returns, enhance food safety, and strengthen the industry’s environmental footprint.
University of California (UC) almond specialists Joe Connell and Bruce Lampinen, UC agricultural engineer Ken Giles, have a roadmap with directions to produce and harvest a safer and cleaner almond crop. The trio shared their findings during the Almond Industry Conference in Modesto, Calif., in December.
The year-long process starts in the winter months, says Connell, UC Cooperative Extension almond farm advisor in Butte County.
“Good orchard management is an ongoing process to ensure the orchard floors are in good shape at harvest,” said Connell who has 30 years of almond experience. “The first step toward a clean harvest is a good job of winter sanitation.”
Connell’s prescription for winter sanitation includes clean orchard strips through contact or pre-emergence weed control. Non-tillage strip weed control provides improved orchard access all year; a firm orchard floor with less dust and a weed-free surface for harvest; reduced tree trunk damage, crown rot, and compaction; improved water penetration in most soils; and higher leaf potassium levels.
“A pre-harvest herbicide application to the row middle helps keep the orchard floor clean and promotes rapid nut drying,” Connell explained. “A clean surface enhances food safety and nut quality.”
Organic weed control is more of a challenge. Propane flamers used down the strips work well with small weed seedlings only. The flame heat should kill the weed, not burn anything.
Another key to orchard sanitation is blowing mummies to the row middle and chopping up to reduce Navel orangeworm problems and avoid potential aflatoxin issues at harvest. Avoid making ruts in wet soil during the winter so harvest equipment can efficiently and effectively move across the orchard floor, Connell says.
Timely and proper brush removal is also important. Brush burning is not allowed in many areas of the San Joaquin Valley due to air quality issues. Chipping and shredding brush are effective.
Keeping vertebrae animals out of orchards also protects the crop. Growers should minimize animal entry into the field, Connell says. Controlling squirrels and other rodents removes reasons for the entry of animal predators including coyotes. Contamination by wildlife closer to harvest increases food safety risks. Consider the field proximity to livestock operations.”
Composted manure as a fertilizer in orchards is a sensitive issue. Connell advises against manure use in almond production. If manure is used, apply the manure in the fall after harvest with soil incorporation followed by watering with rainfall or irrigation. Make sure the manure is well composted. If non-tillage weed management is used, Connell says avoid manure use in the orchard.
Another clean and safe practice is to sanitize harvest equipment and the huller before harvest. Unused equipment draws varmints which can leave droppings and contamination behind. Also, know the source of surface irrigation water. Know where the water came from upstream. If there is any potential for contamination, a water test is a good idea that can help guide treatment if necessary.
A timely harvest helps ensure high nut quality and reduces food safety risks.
“When 100 percent of the lower interior nuts achieve hull split then get the nuts off the tree,”Connell recommended.
Nuts have achieved the maximum dry weight of oils and carbohydrates at 100 percent hull split. Maximum nut removal is possible at this time. Nuts dry faster on the ground than on the tree. Sticktights and shriveled kernel numbers are low. Foreign material plus chipped and broken kernels are minimal. A delayed harvest can increase kernel rejects and moldy kernel percentages.
Timely harvesting can also derail the third-generation egg-laying stage of the Navel orangeworm in mid-to-early August.
“A timely harvest to get the nuts off the tree, swept, picked up, and into stockpiles for later hulling or fumigation is recommended,” Connell said. “Covering the pile protects the nuts from rain.”
Connell is wary of harvesting almonds before 100 percent hull split. An early harvest can increase sticktights, curled hulls, foreign material, and kernel damage at the huller. Timely nut removal from the tree may require longer nut drying on the ground which can increase the risk of ant damage from the southern fire ant and pavement ant so any populations should be monitored.
Meanwhile, a late harvest can increase worm damage, aflatoxin potential, and rain delays. Nut drying is more difficult as the days get shorter and the sun angle in the sky is lower. Ant and worm damage increases.
“Do your best to harvest on time,” Connell concluded. “An on-time harvest preserves nut quality and keeps growers from the many problems associated with rains which were especially common during the harvest last fall.”
Bruce Lampinen, UC integrated orchard management specialist in almonds and walnuts, agrees that orchard management practices can impact food safety risks. Lampinen says heavily canopied orchards increase food safety risks due to wetter, cooler conditions on the orchard floor. Heavier canopies also make nut drying on the ground more difficult especially for late almond varieties.
Hedgerow planting can lead to dense shade under the tree row and increase food safety risks since the area gets less sunlight, Lampinen told the crowd. As the sun moves across the sky, very little light reaches the orchard floor in narrow hedgerows. More conventional tree spacing allows more varied light and temperature patterns across the orchard floor.
“Any orchard with production above 3,500 kernel pounds per acre or 70 percent or more light interception has an increased potential for food safety problems,” Lampinen explained.
Stockpiling excessively wet nuts also increases food safety risks. Stockpiling nuts with green pollenizer nuts can cause problems. Make sure the nuts are adequately dry before stockpiling. Sample the nut moisture content across the orchard before harvest.
“Do not stockpile if either the hull moisture content exceeds 13 percent or the kernel moisture content exceeds 6 percent,” Lampinen said. “This is equivalent to a sample water activity of 0.7 or a relative humidity of 70 percent.”
Choose appropriate tarp materials to minimize potential condensation.
Dust reduction in almond production was discussed by Ken Giles, UC Davis professor in the Department of Biological and Agricultural Engineering.
“We need to be concerned about harvest dust reduction, not just from the regulatory viewpoint but also from a stewardship and good neighbor standpoint, especially in areas near housing,” Giles said.
Giles’ equipment studies have measured visible and non-visible particulate matter dust in almond orchards, through collaborations with the Almond Board of California and Texas A&M University. The work has generated ways to help almond growers tweak the harvesting process to reduce dust emissions and even save money in the process.
Giles’ almond sweeper machine research has measured dust emissions from a sweeper operating with a standard head height compared to the emissions from a head placed one-half inch closer to the ground. Sweeper heads are often lowered one-half inch to gather the last nuts on the orchard floor which increases dust. An optical device in the tests measured the light penetration through the dust cloud.
“Sweeping one-half inch lower produces 33 percent more dust,” Giles’ research revealed. “The harder you work to get every nut the more dust is released.”
The same technical setup also measured the dust output from wire tines versus rubber tines on sweepers. Wire tines generated 35 percent less dust than the rubber tines.
Giles said, “These are all efforts growers can follow to make operations a little cleaner without large investments in time and money.”
Giles also conducted a random trial with newer reduced-path sweepers from several manufacturers; measuring the nut-sweeping efficiency, equipment field time, and fuel costs.
In the conducted tests, reduced-path sweepers were just as efficient as traditional sweepers in removing the nuts from the orchard, the research concluded. The sweepers also reduced the orchard sweeping time by 25 to 30 percent which meant more acres swept per hour and less generated dust. Hourly fuel consumption was higher but the reduced machine running time more than offset the fuel costs.