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 canker, and 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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