California's almond harvest is over, and growers are turning their attention to 2001 with post-harvest management practices - orchard sanitation, irrigation and dormant sprays - all critical to next year's nut quality and yield potential.
"A lot of growers think they do a good job with some of these post-harvest activities, but in reality, they often miss some of the details that can make a huge difference in next year's crop," says Gary Osteen, an independent Pest Control Advisor in Kern County, Calif. "There's not a lot of room for mistakes. A little time invested now will definitely pay dividends next season."
According to Mario Viveros, Kern County University of California Cooperative Extension farm advisor, almond growers should be especially conscientious after harvest. "The first thing he needs to do is recognize the importance of irrigation after harvest," he says. "From the time harvest is finished until the trees lose their leaves, irrigation is extremely important. During that time, we'll lose about 9-10 inches of water in the soil profile. That represents about a third of the season's water use. Growers often don't understand this because it looks like the trees are shutting down."
Actually, the opposite is true, according to Viveros. Root activity increases significantly after harvest and continues throughout the winter months. Trees are beginning to store carbohydrates, nutrients and water that will be held in reserve until the following season. When spring finally arrives and the trees emerge from dormancy, those stored reserves are utilized for initial shoot growth and bloom. Fall irrigation also help relieve some of the pressure on irrigation during the subsequent growing season when the trees are actively growing.
Bob Gaddie another independent PCA who consults on almonds in Kern County says he encourages his growers to put enough water on the field to fill the soil profile down to five feet. "If they do that in the fall, then we can use subsequent irrigations during the growing season to replenish the top part of the profile as needed. Without enough fall irrigation, water management becomes very difficult during the next growing season."
Pruning is another important management practice that should be completed soon after harvest. "There are a lot of advantages to early pruning that are simply common sense," Viveros explains. "By getting to that job right after harvest, the pruners will be able to distinguish between dead wood and actively growing limbs. The ground is usually dry at that time, so the grower can push the debris out of the way so it won't interfere with dormant sprays later on in the winter. And it's just easier to find labor right after harvest."
Zinc sprays Zinc sprays are another consideration after harvest. Zinc deficiencies are fairly common in sandy soils and young, drip-irrigated orchards. While some growers opt to delay zinc sprays until the following season so they can piggyback them with other applications, Viveros says that it's a much better idea to apply zinc in the fall.
"It's important to get zinc on in the fall so the tree is not deficient in zinc for fruit set the following spring," he says. "Zinc is a very important micronutrient that optimizes fruit set."
A zinc application in the fall also provides other advantages. From mid-November until the first of January, almond trees need approximately 600 chilling hours, according to Viveros. That can sometimes be difficult to achieve in the southern part of the Valley.
"A post-harvest zinc application does more than just supply an important micronutrient," Viveros says. "By defoliating the trees and putting them into a dormant state earlier, it appears that we're allowing the trees to accumulate additional chilling hours. I think that's particularly important here in the southern end of the Valley where warmer temperatures often delay dormancy and limit the number of chilling hours that we get."
By defoliating the leaves with a zinc application, a grower also reduces disease problems the following season. "Defoliating the trees helps reduce the amount of inoculum that leads to diseases such as shot hole the following season," Osteen says. "It also helps improve the coverage a grower gets with dormant sprays because the leaves aren't in the way."
Shaking trees to remove mummies and stick-tight nuts is one of the most effective ways a grower has of controlling navel orangeworm. Larvae overwinter in mummies that remain on the tree after harvest. By removing mummies and destroying them during the winter, a grower can significantly reduce navel orangeworm infestations the following season. It's a monotonous job that isn't always carried out with enough consideration to how well the job is being done. Weather can also be a factor. Rain or fog is needed to loosen the mummies and stick-tight nuts so they can be shaken from the tree. In the absence of adequate moisture, it may become necessary to send a poling crew through the orchard to take care of what the mechanical shakers miss.
"After my growers have done their dormant shakes, I go back in and look at the trees," Gaddie says. "If I find an average of one mummy per tree, then I recommend they go back and do some more work."
Osteen agrees. "It's one of those practices that growers tend to rush through, and then they make matters worse by not looking close enough to see what kind of job they've done. It's not difficult to count mummies, but you have to get out there and walk around the entire tree."
Finally, dormant sprays are an integral component of a good winter management program. "Dormant sprays are important to control pests such as peach twig borer and San Jose scale," Osteen says. "Coverage is probably the most critical factor in the efficacy of a dormant spray. A grower should use adequate amounts of water or oil and make sure he's getting good, solid coverage throughout the orchard."
If a grower is going to use an organophosphate for a dormant spray, he should be careful not to delay the application beyond Jan. 15, according to Viveros. "OPs can be very harmful to bees, so you need to wait at least two weeks after an application before you move bee hives into the area," he says. "Other materials, such as Success, can also be harmful to bees, so a grower needs to be careful, remember what he's spraying and take the appropriate steps to avoid problems."
Post-harvest management practices aren't mysterious, nor are they particularly difficult. A little attention to detail and just plain common sense exercised this fall can make a huge difference in next year's crop.
"The guys that do a good job in sanitation after harvest, invariably have a good crop the following year," Gaddie says. "You see it year after year. It's not difficult. You just have to pay attention to what you're doing and understand why you're doing it."