Ways To Reduce Zinc Deficiency in Almond Crops

Faced with the challenge of zinc deficiency while trying to improve his almond trees’ long-term health and productivity, California-based grower Barat Bisabri required a dependable post-harvest nutritional solution.

“Zinc is very important to my nutrition program, and not only in almond production,” says Bisabri, the owner and Managing Partner of Shiraz Ranch in Newman, CA, which, in addition to nearly 600 acres of almonds, boasts 150 acres of pistachios and 600 acres of mandarins. “The variety of almonds that I grow are called ‘Independence’, which is very zinc dependent. So, any zinc deficiencies will be very prevalent in this variety, so we must go a little extra with zinc [in our nutritional program].”

Zinc deficiency is a significant yet common issue for almond growers based in California’s San Joaquin Valley, located in the southern half of the state’s Central Valley agricultural breadbasket. For decades, ‘Nemaguard’ has been the workhorse rootstock of the California almond trade due to its resistance to root-knot nematodes and its compatibility with most commercial almond varieties, including the ‘Independence’ variety.

“The majority of almonds in California are planted on ‘Nemaguard’ rootstock, and that rootstock is poor at mining zinc out of the soil,” Dylan Rogers, the Sales Account Manager for AgroLiquid in Southern California, says. “Therefore, a lot of orchards are zinc deficient.”

Zinc deficiency in almond production creates numerous concerns for growers. Long-term issues include reduced disease resistance, stunted growth, and susceptibility to drought stress.

In the near term, though, Rogers says zinc deficiency can delay the onset of budbreak and bloom, which significantly reduces crop yield due to increased susceptibility to late frosts, uneven fruit set, decreased pollination efficiency, and potential issues with nutrient transport and carbohydrate metabolism, both of which impact kernel weight and almond quality.

“As a grower, if you see these deficiencies show up in your trees, then you’re definitely going to lose some yield,” Rogers says. “So, you’ll want to get that zinc back into the tree at levels sufficient for next year’s crop. Unfortunately, the damage has been done to the current year’s crop. But you can get it turned around and get those leaves growing and maturing for the next season.”

To optimize plant health and productivity, growers commonly incorporate zinc and other essential nutrients into foliar spray programs alongside herbicide and fungicide applications throughout the growing season. However, Rogers says the best bang for a grower’s buck is a postharvest zinc application between October and early November.

“At that time, there’s still good foliage on the trees, and it’s very important to make that application when the leaves are still green and healthy,” he says. “If you get too late into the fall, those leaves will start to harden off and senesce, and you’re not going to get that nutrition into the tree.

“You want to get that zinc into the tree before it shuts down,” he adds. “Think of it this way: The leaves are 90-plus percent of the tree. If you wait until bloom to put that zinc on, you don’t have many — if any — leaves available to help with that uptake. Instead, you’re spraying directly on the wood and buds, and you don’t have the surface area you would have with all the leaves available to you post-harvest.”

A blanket, one-size-fits-all application rate is not practical when managing almond production, Rogers says. So, accurate diagnosis of zinc deficiency through soil and tissue analysis is critical. “Growers are pulling tissue samples multiple times throughout the year,” he says. “Those tissue samples, along with the fact that growers know their soil [composition] really well, factor into the decisions on application rates and what’s needed to get the job done.”

While numerous nutritional products apply zinc post-harvest, Rogers recommends that growers utilize a micronutrient blend with a heavy zinc concentration, such as AgroLiquid’s Micro500, providing a synergistic effect that assists the plant in nutrient uptake. In addition, nutritional products with chelation or encapsulation technology will keep those nutrients available to the plant, prevent them from getting tied up in the soil, and assist that efficacy once the zinc is in the plant.

Bisabri’s nutritional approach addresses his orchards’ zinc needs directly to the roots through fertigation and by foliar applications as part of his routine in-season sprays. He has settled on a nutritional product that offers him consistency, flexibility, and improved yield. In addition, Bisabri says it was important that the product avoided phototoxicity in young leaves, which is critical in his almond and citrus crops.

Bisabri applies the product at a rate of one quart per acre when making a foliar application and two to three quarts per acre when applied to the soil through irrigation. Post-harvest, and once the trees have been irrigated, Bisabri will follow up with a foliar application that includes zinc, boron, urea, and some nitrogen sources to help emerging buds weather the winter months and start strong in the spring.

“The importance of zinc is well known in the grower community,” he adds. “What’s important is finding a product that is compatible, is safer for the plant, and has the best zinc absorption. It’s important that this is a chelated product, too, which does a better job at getting [zinc and other micronutrients] from the soil and into the plant.”