Almond growers in California are facing significant challenges from persistent pest pressures, leading to increased reject rates and financial losses as nuts are delivered to handlers and processors statewide. Key pests like navel orangeworm (NOW), plant bugs and the emerging Carpophilus beetle are contributing to these issues. Industry experts stress that effective orchard sanitation and collaborative efforts among neighboring orchards are crucial strategies for managing these persistent challenges.

Mel Machado, vice president of member relations for Blue Diamond Growers, addressed a room of growers during an almond day hosted by UCCE in Merced in October, painting a picture of this season’s escalating reject rates.

This year’s infestations have led to some of the highest reject levels seen in decades, Machado said, with 2024 standing out as one of the worst years he recalls. While this season has been dominated by NOW and plant bugs, he expressed less concern about Carpophilus beetle, noting minimal significant damage by the beetle halfway through the receiving season. However, Machado noted that this is a “year of learning” regarding Carpophilus as growers in Australia have noted significant challenges in managing the beetle.

Highlighting the variability between northern regions like the Sacramento Valley and the southern San Joaquin Valley, Machado noted that in 2022, the Sacramento Valley experienced lower yields due to a freeze, which intensified pest pressures as fewer nuts meant a higher percentage of damaged nuts.

Gross revenue is another key factor, he explained. While price per pound often dominates conversations, it’s the combination of price and yield that ultimately impacts a grower’s bottom line. Costs per acre vary significantly, especially when considering factors like water prices, which fluctuate widely across regions. In some areas, variable costs might reach $3,000 to $4,000 per acre, putting additional pressure on growers in lower-yield areas, such as parts of the Sacramento Valley, to balance lower revenues against high production costs.

Sanitation and the Neighbor Effect

Humorously asking attendees at the almond day if they had a “crappy” neighbor or might be one themselves, Machado emphasized the influence that poor management practices are having on rising pest pressures.

“Without a doubt, the crappy neighbor has been an influence this year,” he said, noting low-input and non-input orchards as well as the forced deprivation of trees are all root causes of the NOW explosion.

Analyzing the population dynamics of NOW to reveal how easily infestations can spread throughout an almond orchard, Machado explained in a typical 2,500-pound crop with a 30-nut-per-ounce average, an acre can contain around 1.2 million almonds across 110 trees, spaced at an 18-by-22-foot planting pattern. Two mummies left on each tree amounts to approximately 220 mummies per acre, with each capable of sheltering overwintering NOW. If half of those mummies yield surviving female moths, the potential egg count can range from 60 to 200 eggs per female. He added during the first flight emerging from these mummies, infestation rates start around 0.1%. However, by the second flight, which targets highly susceptible varieties like Nonpareil and Independence, infestation levels can reach nearly 3%, underscoring the rapid escalation in pest pressure and the importance of effective NOW management practices.

But it was the third flight that did the most damage this year, Machado said.

“That third flight in the latter half of August hammered a lot of people,” he noted. “The math says you have a potential infestation of about 72%. Naturally, grower’s efforts keep the damage down much lower than that, but we still had growers who did all they could and still suffered reject levels in excess of 20%, all because of neighbor issues.”

If growers feel limited by their neighbors’ management practices, Machado encourages them to be extra mindful of their own sanitation efforts in the coming months. While he acknowledges the challenge of entering an orchard when soil is wet and the ground might be slippery, he emphasizes it’s not a step to skip this year.

“Sanitation will be the foundation of navel orangeworm control without a doubt,” he said. “When you’ve got that many eggs laid in a mummy, you know you’re going to have a problem.”

Jake Wenger, general manager of Salida Hulling, another Modesto-based handler, said while he actually feels reject rates have improved compared to last year, they still reflect ongoing pest pressures and indicate how financial constraints have led some growers to cut back on pest management efforts, impacting reject rates.

He also agrees with the “neighbor effect” and said that even with diligent pest control, nearby neglected orchards can increase overall pest pressures.

“Because of the pricing, you have some people that have made economic decisions for their farm, and they’ve had to cut some sprays out,” Wenger said. “But that doesn’t just affect them because bugs don’t know property lines.”

Operating since 1970, Salida Hulling is a mid-size co-op expected to process about 19 million pounds this season. Wenger noted an often-overlooked factor in pest management is how custom harvesting can influence pest pressures, sometimes leading to missed mummies that disrupt pest cycles. He explained optimizing shake timing can help reduce mummies left in the orchard, noting if nuts aren’t coming off easily, they may not be ready yet. Proper timing, he stressed, is essential for limiting overwintering pests.

“Are the shaker guys shaking the trees correctly and getting all the nuts off? Because if they’re not coming off, is the grower shaking at the appropriate time?” he said.

In addition to sanitation, Machado stressed mating disruption is one of the most effective tactics for controlling NOW. When combined with thorough sanitation practices, mating disruption can substantially reduce pest populations. However, he cautioned relying on any single method without prioritizing sanitation is like “fighting a no-go battle.” Instead, he urged growers to adopt a comprehensive approach, integrating multiple techniques to manage pest pressures effectively while ultimately supporting both yield and quality.

While damage from NOW remains a significant concern, Machado noted a significant increase in crop damage this year due to brown spot (deep blemishes on the kernel caused by the feeding of stink bugs or leaf-footed plant bugs).

“I saw more brown spot on Nonpareil this year than I’ve ever seen before,” he said. “As a percentage of the damage, it’s really elevated.”

Brown spot has particularly affected varieties like Independence, Price and Sonora, Machado said. Brown spot damage has been increasing over the past few years, adding to the financial losses growers have been enduring.

In addressing pest and disease control for the future, Machado emphasized the importance of industry collaboration by leveraging resources from The Almond Board of California and other industry experts. Integrated pest management strategies emphasizing a thorough understanding of the life cycle and development of each pest species will continue to be essential in sustaining California’s almond production amid ongoing challenges.