PPDL Picture of the Week

February 8, 2016

Sub-lethal Glyphosate Injury in Ornamentals

Kyle Daniel, Nursery and Landscape Outreach Specialist, Department of Horticulture and Landscape Architecture

Glyphosate is one of the most commonly used herbicides in the nursery and landscape.  The combination of the various attributes, such as limited soil activity, broad spectrum of weeds controlled, systemic activity, ease of use, very low volatility, and others make glyphosate a common tool for nursery and landscape weed control.  Though the glyphosate herbicide has been on the market for many years, it wasn’t until glyphosate went off patent that the various carriers and new surfactants were incorporated in the newer glyphosate products.  Because of these newer, more effective products, glyphosate is not safe to spray on the bark of trees, whether deliberately or via drift. 

 

Some signs and symptoms of glyphosate damage in ornamental plants include:

·       Bark cracking

·       Witches broom

·       Chlorosis

·       Necrosis

·       Dieback

·       Stunting

·       Loss of apical dominance

·       Epinasty

·       Clubbed roots

·       Death

 

To prevent glyphosate damage in ornamentals plantings use a preemergence herbicide in the spring and fall, use a shield when applying glyphosate around ornamental plants, never use glyphosate as a sucker removal product, and reduce the amount of glyphosate used around ornamentals.


Click to enlarge image


 

Figure 1. Glyphosate injury when applied to the bark of this tree 

 

Figure 2. A crack in the bark that does not heal properly after glyphosate was applied to the bark with a pruning injury.



Figure 3. Redbud stems after freezing and applying a glyphosate product (Roundup Original Max) to a temperature of -6 degrees F.