Glufosinate Trunk Injury of Young Almond Trees

Glufosinate (Rely 280 and other trade names) usage has increased over the past year due to the increase supply and availability of generics. This herbicide has been shown to be very effective in controlling glyphosate resistant weeds, including fleabane, marestail, and goosegrass and has an important role in orchard weed control.

Glufosinate drift can cause trunk damage to young almond trees. Photo courtesy of Brad Hansen, UC Davis

Glufosinate drift can cause trunk damage to young almond trees. Photo courtesy of Brad Hanson, UCCE Weed Specialist

One concern of glufosinate usage is plant safety. Accidental applications of glufosinate to the trunk of one to three year old almond trees can cause damage. Field observations and studies by Brad Hanson (UC Weed Specialist) have shown that gumming and a sunken canker can occur three to four weeks post herbicide application. This canker is distinctively different from Phytophthora, band cankerand bacterial canker as there is more consistency of symptoms across the field (i.e. a pattern in symptom occurrence). Within affected trees, symptoms include origination of the irregular shaped canker being above the soil line and in a similar location on multiple trees, the lack of a “sweet” smell, and amber gumming.

Gumming of the tree trunk caused by experimental glufosinate application. Photo courtesy of Brad Hansen.

Gumming of the tree trunk caused by experimental glufosinate application. Photo courtesy of Brad Hanson.

Although the damage appears to be a severe issue, most observed damage has resulted in slightly smaller, mis-shaped trunks. Within a few years – and usually by the first harvest -affected areas appear to be compartmentalized by the enlarging trunk and are rarely visible. Tree loss has not been observed in normal drift incidences.

Glufosinate is a useful tool for post-emergent weed control. As with any herbicide, its use should be used with caution around young trees. Avoid spraying in windy conditions and use the right equipment and pressure to avoid drift.

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4 thoughts on “Glufosinate Trunk Injury of Young Almond Trees

  1. We looked at this problem 6 years ago on 3rd leaf trees. My recommendation has always been to refrain from usage unless there is calised bark or a tree protector present.

    1. Thanks for your comment, Mark!
      I agree, this problem was quite common several years ago when glufosinate was readily available in CA. Once it became scarce, it was no longer an issue. Now that generics are hitting the market, use within orchards has increased and damage is being found.

      Keeping on the tree protectors do help protect the trunk. Having them on for multiple years, however, does increase the chance of other issues – especially when soil and debris begin to fill the protector.

      I usually suggest keeping them on through the summer of the second year as it provides protection for the late spring burn down while still giving an opportunity to remove them before debris and tree growth makes it more difficult.


    1. Sara,
      I am unsure of the rates, but my guess is that it is a small proportion of the treated acreage. The issue was severe enough, however, to establish a research project to prove that glufosinate can cause damage. I feel that many farmers are mis-interpreting the information. Instead of viewing it as a problem that can prevented through the proper use of herbicide, it is perceived that the product shouldn’t be used. My perpspective, rather, is that people should be aware that spraying this material on the trunk of their trees will have an impact and thus should be avoided.

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