Glufosinate herbicide use has increased over the last year due to the increased supply and availability of generics, according to David Doll, University of California Cooperative Extension (UCCE) pomology farm advisor in Merced County.

Doll says glufosinate is very effective in controlling glyphosate-resistant weeds, including fleabane, goosegrass and marestail. It is also an important control product for orchard weeds.

Yet plant safety is one concern of glufosinate use at the trunk level, Doll notes. An accidental application to the trunk of one-to-three-year-old almond trees can result in slight trunk damage.

“The damage symptoms can include the origination of an irregular-shaped canker above the soil line and, in a similar location on multiple trees, the lack of a ‘sweet’ smell, and amber gumming,” according to Doll.

Although the damage appears severe, most damage seen is slightly smaller, misshapen trunks.

In field observations and studies by Brad Hanson, the University of California weed specialist says gumming and a sunken canker can occur three to five weeks after a herbicide application.

A glufosinate-caused canker is different from Phytophthora, bacterial canker and band canker. There is more consistency of symptoms across the field – a pattern in symptom occurrence.

Within a few years – and usually by the first harvest – Doll says affected areas appear compartmentalized by the enlarging trunk and are rarely visible.

“Tree loss has not been observed in normal drift incidences.”

Doll calls glufosinate a useful tool for postemergent weed control.

As with any herbicide, he recommends grower use with caution around young trees and to avoid sprays in windy conditions.

Use the right equipment and pressure to avoid spray drift.

Dr. David Doll is the University of California Cooperative Extension pomology farm advisor in Merced County. This information is from The Almond Doctor website and is used with Dr. Doll’s permission.