Planning for your summer tree nut weed control

Written by: Kurt Hembree, UCCE Farm Advisor, Fresno County

Winter weeds were abundant this year, thanks to the high amount of rainfall we had. Hopefully you found time between storms and were able to get into your orchards and treat for weeds. Given moist soil conditions and warming temperatures close at hand, summer weed growth is also expected to be high. So, are you ready to go with your summer weed control program?

Hopefully you already know what weeds you’ll be up against. If not, look to see if there are new ones emerging in recently-watered orchards or after the last rainfall. Note specific weeds so herbicide(s) can be selected accordingly. When it comes to herbicide selection, make sure you’re using products that are effective against your specific weeds, which often vary from field to field. Also, select herbicides and rates that are appropriate for the soil type; lower rates of preemergent products are often needed on sandier soils than heavier soils. Consider using sequential treatments where appropriate if rainfall occurs in April, which can help extend control through summer.

Remember to add postemergent products to the tank if weeds are already up and growing when you treat. If glyphosate-resistant horseweed, hairy fleabane, junglerice, or ryegrass are present, and you still want to use Roundup or a similar material, be sure to add another burn-down material that is effective on those weeds. Combining Treevix or Rely 280, Lifeline, or similar product with Roundup has worked well on these and a wide variety of weeds. Be sure to treat when the weeds are small for optimum control. Don’t wait to spray when weeds are large, droughty, or dense, or herbicide coverage and performance may suffer. Use spray tips, a spray volume, and spray pressure that adequately wets the weeds, while minimizes spray drift.

To make your tree nut weed control efforts the most effective and efficient they can be, consider these important measures before treating:

  • Make sure spray equipment is functioning properly and has been recently calibrated. You should have ample spray equipment and labor available to ensure treatments are timely.
  • Select herbicides and rates based on the specific weeds present or expected. Each orchard may have different weeds, so adjust herbicide mixes accordingly.
  • Use spray nozzle tips, a spray pressure, and a travel speed that is adequate for the desired coverage of the herbicide type(s) (contact, systemic, and preemergent) being used. Use drift-reducing spray tips and/or spray shields where possible to help mitigate spray drift concerns.
  • Make sure postemergent materials are applied to small, succulent weeds within two to three weeks after emergence. Preemergent materials need to be applied within 14-21 days of rainfall or irrigation.

Evaluate the performance of each treatment and adjust the next treatments accordingly.

It is also very important to rotate or tank-mix herbicides with different mode of actions (MOA) whenever possible to reduce the risk of herbicide-resistant weed development and preserve herbicide effectiveness. Following is a list of registered herbicides in California perennial tree nut crops, along with their specific MOA group numbers and sites of action. To rotate and/or tank-mix herbicides effectively, simply select specific herbicide products for your specific nut crop type with different active ingredient MOA group numbers. Herbicides and their mode of actions registered in tree nuts in California.

MOA (group) MOA

(site of activity)


(active ingredient)


(product example)

1 Acetyl CoA carboxylase fluazifop



Fusilade DX

Select Max


2 Acetolactate synthase flazasulfuron


penoxsulam (2) + oxyfluorfen (14)


Matrix FNV

Pindar GT

3 Microtubule assembly oryzalin



Surflan A.S.

Prowl H2O

Treflan HFP

4 Synthetic auxin 2,4-D amine Orchard Master
5 Photosystem II simazine Princep
7 Photosystem II diuron Direx
8 Lipid synthesis EPTC Eptam
9 EPSP synthase glyphosate Roundup
10 Glutamine synthase glufosinate Rely 280, Lifeline
12 Carotenoid biosynthesis norflurazon Solicam
14 Protoporphyrinogen oxidase carfentrazone










21 Cellulose biosynthesis isoxaben Trellis
22 Photosystem-I-electron diversion paraquat Gramoxone Inteon
27 Hydroxyphenylpyruvate dioxygenase mesotrione Broadworks
29 Cellulose biosynthesis indaziflam Alion
This is not an endorsement for any of the trade names listed, nor does the omission of specific trade names reflect the view of the author. Refer to your local chemical dealer or manufacturer for specific herbicide products available. Consult the manufacturer’s labels for specific crop and treatment recommendations.

Kurt Hembree, UCCE, Fresno County. November 2015. (

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