May/June 2024
Using resources, tools to help manage unwanted pest threats on the West Coast
In the heart of California’s nut-growing region, Jhalendra P. Rijal, area integrated pest management advisor for the University of California Cooperative Extension in Modesto, has experience in dealing with unwanted pests in tree nut crops. In a recent interview, he provided some insights into sustainable pest management strategies that focus on environmentally friendly practices.
Rijal delved into two notorious pests — the navel orangeworm (NOW) and the brown marmorated stink bug (BMSB) — and a new one, the Carpophilus beetle. He specializes in various applied entomology and pest management research focusing on major tree fruit and nut pests in California.
One of the priority areas of his research is invasive pests. In the last 10 years, Rijal has worked on high impact invasive pests that include BMSB, spotted wing drosophila (SWD) and, most recently, Carpophilus beetle (Carpophilus truncatus).
During a recent interview, he was asked about environmentally friendly or sustainable pest management strategies growers can integrate into their IPM plans and also about what pest threats are on top of the list for this year.
Tree nut grower challenges
Among the emerging challenges faced by growers, Rijal highlighted threats posed by economics, NOW, the Carpophilus beetle and BMSB. He also revealed concerns about threats on the horizon.
Economic trends
Rijal shared that with the downturn of crop prices across the industry, growers are faced with a reality of expenses versus revenue.
“If anything changes, it has to be economics. With low commodity price and higher input costs, growers are forced to tolerate more pest pressure and/or damage in general, but at the same time, don’t want to abandon pest management practices,” he said.
Despite the efficacy of these approaches, Rijal acknowledged the economic challenges growers face. “Economics is a significant factor,” he said.
With fluctuating crop prices, striking a balance between pest management costs and revenue becomes paramount. However, Rijal asserted that the long-term benefits of sustainable pest management outweigh the initial investment.
Navel orangeworm concerns
Regarding NOW, Rijal noted a concerning trend of high pressure in recent years. He emphasized the critical importance of cultural practices such as mummy sanitation and well-timed insecticide application during hull/husk split when the nuts become susceptible to NOW infestation. Failure to apply preventive measures at this stage can result in significant crop losses.
In 2022, NOW was a big deal, and he noted that California had a four times higher state average compared to normal years.
“We’d like to see mummy sanitation at a higher rate/ percentage,” he said. “It hasn’t improved much this year either. Mummy sanitation is the foundation of NOW management.”
“As soon as hull split happens, (it) becomes susceptible to NOW,” he said. “The timing is important to time the hull split spray. If you miss the timing by five to seven days, you miss a lot, as eggs can hatch within five days or so in July temperatures. Timing for the first spray at 1% hull split is critical. If economics makes sense, it is highly advisable to integrate mating disruption for long-term control of NOW. Mating disruption is the ‘green’ technology that fits well with the IPM practice.”
Battling Carphopolius beetles
The Carphopolius beetle is definitely a challenge, he also emphasized. “I know as I’m the person who is visiting growers that have the damage,” he said. He shared that he has visited 12 to 15 almond orchards with the beetle infestation.
“I was surprised at how much pressure these insects are causing,” Rijal said. “And it is the first season that we are dealing with this pest. As Extension personnel, we are definitely nervous about this pest.”
He said that the Carpophilus beetle has scavenger feeding habits and can survive on mummy nuts — the relatively humid environment at the soil/mummy nuts interface seems to be favorable for them to survive.
“One thing we know is that these beetles overwinter on mummy nuts, mostly ground mummies. Anything growers can do, especially when infestations are discovered, is to destroy the ground mummy nuts with effective flair mowing,” Rijal said. “This will help combat the Carpophilus beetle. Growers may need two passes to destroy the beetles.”
Winter sanitation is critical and also the fundamental way to manage NOW.
“There is nothing we currently know about insecticides to provide control as this is a very new pest for us,” he said.
Rijal and Wilson Houston, associate cooperative Extension specialist director at the UC Organic Agriculture Institute, Kearney Agricultural Research and Extension Center Department of Entomology, UC Riverside, are poised to conduct insecticide trials to determine any impact. Houston shared that he expects to have some results from Carpophilus beetle insecticide research by the end of the year to provide additional information for growers.
A majority of the orchards affected by this pest are almond orchards, but the beetle has damaged pistachios in central San Joaquin Valley and Rijal said that late last year, he found the first report in a walnut orchard in Stanislaus County.
“So, they can feed on other nuts,” he explained.
Increases in brown spot
Rijal shared that there is also an increase in brown spot, caused by piercing, mouth-sucking insects, such as the stink bug species and leaf-footed bug, which have increased pressure on crop production.
Based upon his research samples from the San Joaquin Valley, about 2% of crop damage was caused from stink bugs in 2023. He advised growers to pay close attention in the months of April through June when the insects are most active and cause the most damage. In the last several years, invasive BMSB has established populations and have been causing damage.
“During the third week of March, we started capturing BMSB in traps,” he shared.
Rijal is actively researching BMSB in almonds, which the Almond Board of California (ABC) is funding.
“When established in an area, they can cause significant economic damage by feeding seasonal nuts pretty much throughout the season and growers have to spray to reduce the damage,” he said.
He noted that in the southern San Joaquin County area, the pest is not spreading as rapidly. Rijal said that the difference in the spread of the pest may be related to a much drier environment and higher temperatures, and BMSB might have been acclimatizing.
Prepping for spotted lanternflies
Although California has no infestations of invasive spotted lanternfly yet, Rijal noted that he is “nervous about it,” as he knows of the rapid spread of this pest on the East Coast. In early April, he delivered a talk to grape growers about the spotted lanternfly concerns and what role we can play in keeping it out of California.
“They are not here yet, but several interceptions have occurred on the state border in the last two to three years, based upon reports,” he said. “It could be just a matter of time, and that we need to be prepared.”
Control efforts
Rijal advocated for a holistic approach to pest management, emphasizing cultural practices as a cornerstone.
“Winter sanitization and early harvest are two highly effective non-insecticidal practices,” Rijal said. “Early harvest is also a consideration — plan to harvest a few days earlier and growers will reduce the amount of damage.”
He noted that by implementing these control methods along with effective season-long monitoring of pests, growers and pest control advisers can understand the pest pressure in orchards, thereby mitigating damage caused by pests like NOW, Carpophilus beetle and BMSB.
For growers considering insecticide use, Rijal recommended a strategic approach.
“Along with other practices, one to two well-timed applications during hull split, based on monitoring data, can provide good control of NOW,” he advised.
In addition, mating disruption is a “green” technology with little or no impact on the environment and a proven method to reduce NOW damage when integrated with other practices. Implementing these multiple practices mentioned above can help achieve long-term management of NOW.
Additionally, ABC, Rijal and his UC colleagues are promoting NOW mating disruption tools and are fostering grower-to-grower communication and relationship to implement these innovative strategies in a more impactful way with a neighborhood (or areawide) approach.
“Use of mating disruption in the early part of the season,” Rijal recommended. His published work, tinyurl. com/28749vc8, detailed how if mating disruption is integrated into production practices, it can reduce the damage by about 50%.
For brown spot caused by stink bugs and leaf-footed bugs, depending on the time of the year and the pest population, insecticide applications may be warranted. The dilemma faced by growers is that broad-based insecticides can kill beneficials as well.
As the nut growing season progresses, Rijal’s expertise can assist growers navigating the complex landscape of pest management. By integrating sustainable practices and fostering collaboration, growers can safeguard orchards while ensuring environmental stewardship.
