Mar 9, 2021
Weeds experts share guidance for growers, PCAs at TAC 2020

The opportune window to conduct spring monitoring for certain weed issues is right around the corner. And it’s not a time frame that growers want to miss. Uncontrolled weeds can compete with young trees for water and key nutrients in the soil and present problems at harvest in orchards of any age.

Fortunately, the process of monitoring for issues, identifying what’s happening in the orchard, and creating a management plan is not one that growers or even pest control advisers (PCAs) have to go alone.

At The Almond Conference (TAC) 2020, attendees of the session “Effective Weed Management Considerations” heard from Drew Wolter, senior specialist in pest management at the Almond Board of California (ABC), and Brad Hanson, a weed science specialist at University of California Cooperative Extension (UCCE), who broke down key weeds to monitor this crop year and offered research-backed management tips to support growers and PCAs as they strive to make strategic decisions.

Step one: identify the issue

Wolter and Hanson emphasized that the first step in addressing weed issues is to identify exactly what is in the orchard.

“You must determine what you’re up against,” advised Hanson, who mentioned that while some species may look similar, they can have drastically different management requirements. Accurately identifying weed species is therefore crucial because herbicide recommendations as well as mechanical and cultural control strategies vary depending upon the weed species.

“Lots of failures of weed management programs are failures of weed identification,” he noted.

Wolter recommended that growers perform weed scouting regularly, but especially at the beginning of the year and again post-harvest. Jumping on problems early in the crop year is vital to ensuring effective management.

“Most weed species are much more challenging to manage as they mature,” said Wolter, “so it’s better to nip them in the bud before they grow too large.”

Special considerations for young orchards

It is especially vital to identify and combat weeds in young orchards, Wolter said, because in those cases more sunlight can reach the ground as compared to mature orchards with a thicker canopy. More sun promotes greater species composition with several different grasses and broadleaves that need to be controlled by the few herbicides available for young orchards. He recommended applying a pre-emergent herbicide soon after young trees are planted and maintaining a weed-free strip at least 30 inches from the trunk on either side of the tree to prevent weeds from competing with new trees. He warned, however, to make sure the soil is settled so that herbicides don’t move into the root zone during irrigation.

Wolter also advised growers with young orchards to pay close attention to nozzle settings and angles and spray heights, and to be cautious of herbicide drift in windy conditions that can potentially harm young green bark on trunks and low-hanging branches.

Step two: get to know your foe

Once growers identify what weed/s they’re dealing with, the next step is to form an idea of how those weeds operate in the orchard. Hanson said growers should develop an understanding of the biology of the weeds – when they emerge, when they grow and when they produce seeds – “that will help you make decisions about how to time control strategies and interventions more appropriately,” he said.

Wolter directed growers and PCAs to the UC Integrated Pest Management website, where they will find a weed photo gallery to help them identify weeds, information on the makeup of those weeds and much more. Growers and PCAs also are encouraged to contact their local farm advisors for help in understand the basic biological framework for the weeds.

Step three: timely, thoughtful treatment

Once the weeds are identified and more is known about them, it’s time to determine appropriate treatment options. If an application is needed, before each spray growers are advised to consider the “four Rs” of herbicide use: right time, right place, right rate, and right rotation. Wolter said growers should keep detailed notes of their sprays – including the treatment list, weeds present in the orchard during scouting events and knowledge of the species that have been confirmed as resistant in the region – so they have record of which could develop resistance to the herbicides applied.

Though spraying pre- and post-emergent herbicides is the most common form of weed management, there are other ways to control them. For instance, some growers have found that cover crops planted between orchard rows can “out-compete” weeds, while others find most success in mowing and tilling.

Taking a more big-picture approach to weed management, Hanson challenged growers to honestly assess their tolerance for weeds and their need to eradicate them, particularly as it relates to reducing applications in the orchard and helping the industry move the needle toward its 2025 Goal of increasing the adoption of environmentally friendly pest management tools.

For instance, Hanson estimated that if spraying widths were narrowed by even a foot in the roughly 1.4 million acres of almonds in California, the amount of treated land could be reduced by 60,000 acres per application. With most growers spraying three or four times a year, Hanson said, that could mean 200,000 or more fewer acres being sprayed annually with herbicides.

“A relatively minor change could have significant impact across the industry,” he said, adding, “There are opportunities throughout the year to reduce intensity. Be very truthful and thoughtful about what your goals are and the best program to achieve them.”

Growers and PCAs seeking further guidance on weed issues are encouraged to contact the farm advisor/s in their area: Visit ABC’s Industry Directory at and select the “Education, Extension & Publications” resource category to see a list of UCCE staff throughout the growing region.

For more information on this TAC 2020 session, growers and PCAs are encouraged to visit to view the PowerPoint presentation used during the session. Those interested to view recordings from other sessions at TAC 2020 are invited to visit ABC’s The Almond Conference 2020 YouTube playlist.

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