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Breaking Out of the Navel Orangeworm Cycle

Almond acres continue to increase, summer temperatures are trending up and, seemingly, so should the navel orangeworm (NOW) threat. Right?

Not the case during the 2020 season, which saw a drop in NOW population and damage, allowing almond growers to catch their breath. But one down year doesn’t mean a downward trajectory for NOW should be expected in the ensuing seasons.

Navel Orangeworm Populations Observed Through Adult Trapping
Dr. Joel Siegel, 2017-2020

Almond data
While overall population of NOW pressure in 2020 appears to have decreased over previous years, data shows an increased number of NOW emergences. This increased number of NOW emergences is suggestive of their ability to continually adapt to align with key almond vulnerability periods throughout the season.


It’s more important than ever heading into the 2021 season to stay on top of and be proactive against NOW. The outcome of the 2020 season has created an opportunity for growers to gain a step on the pest. Being diligent with a management strategy will be key to continuing to minimize the effects of NOW this season and beyond.

The foundation of a successful NOW management strategy starts with the sanitation of trees, followed by the removal and destruction of mummy nuts in the fall and winter. These fundamentals proved impactful in suppressing populations in 2020.

Impact of Mummies on Future NOW Populations*

Growers with more than one mummy per tree can expect severe reject levels at harvest.

Mummies Per Tree Mummies Per Acre Eggs/a Spring Eggs/a in June/July Eggs/a in August with hull split spray Eggs/a in August (no hull split spray)













*Blue Diamond Growers Almond Facts, November-December 2020.

Unfortunately, this first line of defense is often not enough. A spring insecticide spray in mid to late April may be necessary to take out eggs and hatching larvae. The University of California recommends a reduced risk product (non-pyrethroid) to prevent secondary pest outbreaks. In addition, selecting a single active ingredient (A.I.) product that can be rotated to other single A.I. insecticide applications aligns with industry IPM best practices.

From Nick Gilliam’s perspective, Altacor® insect control powered by Rynaxypyr® active (Group 28) checks all those boxes. As a pest control advisor for Helena Agri-Enterprises based in Kerman, Calif., he recommends Altacor insect control because of its unique mode of action and ability to rotate well with other chemistries.

“Altacor [insect control] couples unmatched residual control with adult mortality and only presents one active ingredient, one mode of action. This is a feature unmatched by other chemistries in its class, which allows me flexibility to effectively manage resistance and pests,” Gilliam says.


Timing is everything when managing for NOW. That’s why Joel Siegel, Ph.D., research entomologist with the USDA Agricultural Research Service and coordinator of the USDA NOW Research Program, proposes using Altacor insect control at early hull split (the most effective single spray is at the initiation of hull split) to take advantage of its long residual control.

“Our recommendation is to use Altacor insect control for that key early hull split application. It is highly toxic to larvae when ingested, has good activity against NOW eggs and also has activity on adults. In addition, growers can make two Altacor insect control sprays 10 days apart to protect newly exposed, vulnerable nut tissue,” Siegel says.

Siegel notes that when making back-to-back sprays 10 days apart, apply at at the full 4.5 oz./A rate. He also recommends growers never skip a row and spray at a speed of 2 mph.


As almond bearing acres are expected to reach 1.26 million acres in 2021 and thousands of acres inching toward maturity, the threat of NOW will only heighten and worsen unless regimented action is taken. Solutions like Altacor insect control are proven tools that pay long-term benefits to an orchard and play an intricate role in stemming the pest’s presence today and in the future.

Always read and follow all label directions, precautions and restrictions for use. Some products may not be registered for sale or use in all states. FMC, the FMC logo, Altacor and Rynaxypyr are trademarks of FMC Corporation or an affiliate. ©2021 FMC Corporation. All rights reserved. 21-FMC-0145 01/21