Glyphosate-Resistant Weeds in Orchards – Recent UC IPM Publications

Last winter, I particpated in a series of seven half-day workshops in California, Oregon, and Washington on herbicide-resistant weeds.  These workshops were organized by Kassim Al-Khatib from the Univeristy of California Integrated Pest Management (IPM) Program and had a special focus on glyphosate-resistant weeds in tree and vine crops.

In preparation for these workshops, we wrote a series of extension publications that I wanted to share today.  The publications and resulting presentations were prepared by weed scientists from various Universities, Cooperative Extension, and USDA-ARS and included various aspects of herbicide resistance in permanent crops.  Even as somone who thinks about herbicide resistance every day, I found the bulletins and presentations to be tremendously informative.  These included:

Selection Pressure, Shifting Populations, and Herbicide Resistance and Tolerance by Brad Hanson, Albert Fischer, Anil Shrestha, Marie Jasieniuk, Ed Peachey, Rick Boydston, Tim Miller, Kassim Al-Khatib. PPT slide handouts available here:

Glyphosate Stewardship: Keeping an Effective Herbicide Effective by Tim Miller, Brad Hanson, Ed Peachey, Rick Boydston, Kassim Al-Khatib

Preventing and Managing Glyphosate-Resistant Weeds in Orchards and Vineyards by Ed Peachey, Rick Boydston, Brad Hanson, Kassim Al-Khatib

Managing Glyphosate-Resistant Weeds in Glyphosate-Resistant Crops by Kassim Al-Khatib, Brad Hanson, Tim Miller, Ed Peachey, Rick Boydston

These bulletins are being published by UC-IPM and the near-final versions are available right now  at this link.  Or at: http://www.ipm.ucdavis.edu/IPMPROJECT/glyphosateresistance.html.

Take care, Brad

Read more orchard weed management blog posts at UC Weed Science

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4 thoughts on “Glyphosate-Resistant Weeds in Orchards – Recent UC IPM Publications

  1. There are a number of new miniature hair sheep breeds (microsheep) that are in the breeding pipeline specifically for tree crops looking to ditch their herbicide dependence. We simply have little choice but to embrace these tot sized grazers in our weed management programs. At the end of the day, herbicide prices have one way and that is up for 2 reasons:
    1. The off patent generics have already enjoyed a very pleasurable deflationary period in prices. They simply can’t get any cheaper.
    2. New herbicide chemistries are generally covered by patent meaning they will not be cheap. the more you need them, the pricier they will be to use.


    1. Hello Aaron, Thanks for your comment. There have been several studies that have shown that grazing animals are effective vegetation managers and can be “trained” to eat only the unwanted vegetation, not the crop. The major issue, however, is the amount of animal waste that is created within the orchard system. Since almonds are shaken to the ground for drying and harvesting, this puts the food in contact with the animal excrement, and thus at a risk for contamination by pathogens that cause food-borne illnesses. Food safety better management practices indicate that having animals within the orchard is not a good practice for safe food and, more importantly, the health of the downstream consumer.


  2. Hi David, I would have thought that the risk of faecal contamination could easily be managed by careful planning of grazing timing. Sheep could be used over the winter period and into the growing season before being removed to allow droppings to break down prior to harvest. In any case, presumably there are other wild mammals in your environment that would deficate in the orchards all throughout the year so the contamination risk must be managed anyway.

    With the current shortage of glufosinate and price rises across the board in glyphosate, glufosinate and the bipyridyls, a warning shot is being sent across the bow of all tree crop managers who rely on these herbicides for weed control. An integrated approach is essential to a future where you have some control over the input cost base. Good luck.


    1. True, there would be a reduction of faecal contamination if grazing was limited to the winter and early spring months. The only issue is that our most problematic weeds are not “winter” weeds, but grow and flower during the summer months (including most glyphosate resistant weeds).

      Research within the area of using grazing animals for weed control has been conducted by the University of California – Morgan Doran has looked at multiple systems in which to graze sheep for weed control. He has found it to be effective in many systems.

      In other words, it’s not that it isn’t a feasible practice, but rather a practice that the marketers don’t recommend (as well as the Almond Board of California). Since they buy and sell the almonds, their concerns are quite valid.

      The argument about other wild animals is a bit of a red herring. Yes, there are things that you can’t control – but there are things that you can. Just because you can’t control one aspect about food safety doesn’t mean you should throw all good management practices out the window.


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