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TNFP1003-tim-hearden-weed-mgmt_BT_Edits.jpg Tim Hearden
A well-maintained almond orchard blooms near Yuba City, Calif., in 2018. Advisors say post-harvest weed management is a critical step for tree nut growers.

Post-harvest weed management a critical step

Growers urged to ‘really know’ the weeds they’re trying to control

When it comes to effective weed management in the orchard, most experienced tree nut farmers are familiar with the level of weed pressure they will experience each year and the types and varieties of troublesome invasive plants that will challenge their annual weed management plan.

But as most farmers know, familiarity with challenges on the farm doesn’t always guarantee a positive or desired outcome.

In addition to the possible introduction of new types of weeds in an orchard system in any given year, there is also the growing problem of weed resistance.  

“If I could make one critical point for growers and PCAs (Pest Control Advisors) making weed control decisions in tree nut systems, I’d encourage them to really know the weeds they are trying to control and understand the strengths, weaknesses, and risks of the control strategies at their disposal,” said Dr. Brad Hanson, extension weed specialist and Vice Chair of Outreach and Extension at the University of California, Davis.

He warns there are no “one size fits all” approaches to orchard weed management.

“Weed spectrum, orchard age and irrigation system, soil types, and manager expectations all play into weed management decisions,” he added.

Fall weed management starts with equipment prep

By the numbers, good post-harvest weed management starts with equipment that is well-tuned and ready for efficient use.

“The key to effective weed management is to make certain that your equipment is ready to go,” advises Kurt Hembree, University of California Cooperative Extension weed management advisor in Fresno County. “If you have your own equipment, the most critical thing is to make certain your pump is working properly, and your spray nozzles are clean and ready to go.”

Hembree says at this point fall rains are nearly a month or so away and if a burn down is necessary following harvest, late Sept. or early Oct. is a good time to get that accomplished.

He says once the rains start, growers in his region can expect to see the emergence of weeds like filaree, annual sowthistle, malva, horseweed and hairy fleabane. Early identification of those weeds is important in knowing what tools to use to avoid an outbreak before it gets started.

“You can always ask your PCA, farm advisor or chemical rep to aid in identification if you see something you’re not familiar with. There is also lots of information available online to help identify weeds,” he said.

Another good resource is the University of California integrated pest management website that provides photos of weed varieties.

“The preferred method of weed control is to apply a combination of soil-residual, or preemergent herbicides, followed by timely foliar, or post-emergent sprays, when weeds emerge later,” he recommends.

Hembree advises your weed “to do” list should take into consideration appropriate herbicide selection, the use of at least two modes of action on weeds, proper sprayer calibration and appropriate sprayer pressure.


  • Use the highest label rate of herbicide(s) for difficult weeds to control.
  • Add buffering agents, surfactants, or other additives as required on the label.
  • Treat when the weeds are best controlled, according to the label.
  • Select nozzles and a spray pressure that provides good spray coverage.
  • Spray under favorable environmental conditions to minimize spray drift.
  • Have the person spraying monitor the application closely and resolve problems as they occur.

Hembree warns glyphosate is weak on some types of weeds and reminds growers that weed resistance is a growing problem that demands attention.

Avoiding over-treatment

“Given the intensity of our tree nut cropping systems, at times, I think we’re as likely to over treat as we are to under treat some of our orchards which can bring in economic, crop safety, environmental, and regulatory challenges,” adds Hanson.

“From an herbicide perspective, tree nut growers have quite a few good tools at their disposal and it’s up to us as weed managers to use them effectively and safely.  I think the answer to many of our weed problems is not necessarily more herbicide, but more thoughtful and timely use of herbicide programs that are based on an understanding of weed biology and herbicide action,” he added.

For more news on tree nuts as reported by growers and farm advisors, subscribe to the Tree Nut Farm Press e-newsletter.

TAGS: Weeds
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