Skip to main content
ARS Home » Midwest Area » St. Paul, Minnesota » Plant Science Research » Research » Publications at this Location » Publication #370149

Research Project: Enhanced Alfalfa Germplasm and Genomic Resources for Yield, Quality, and Environmental Protection

Location: Plant Science Research

Title: Roundup ready alfalfa injury

item GETTS, TOM - University Of California
item WILSON, ROB - University Of California
item GIULIANO, GALDI - University Of California
item LOVELAND, CHET - University Of California
item Samac, Deborah - Debby
item CREECH, EARL - Utah State University

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/19/2019
Publication Date: 11/19/2019
Citation: Getts, T., Wilson, R., Giuliano, G., Loveland, C., Samac, D.A., Creech, E. 2019. Roundup ready alfalfa injury[abstract]. Proceedings of the Western Alfalfa and Forage Symposium. November 19-21, 2019, Reno, Nevada. p. 1.

Interpretive Summary:

Technical Abstract: Since the second release in 2011, the Roundup Ready (RR) alfalfa technology has given growers an excellent tool, allowing control of difficult weeds while increasing the flexibility of herbicide application timing. Initial screening of the technology provided excellent crop safety at all application timings. In 2014, there was an initial observation of injury to Roundup Ready alfalfa after glyphosate application was followed by frost. Symptomology observed included necrosis of individual stems, as well as stunting of the crop. Replicated field trials in 2015, 2016 and 2017 confirmed these same symptoms regularly occur when glyphosate is applied to RR alfalfa followed by frost in Northern California. The field trials also documented first cutting yield was reduced up to 0.8 ton/acre compared to the untreated control at multiple sites. Yield reduction was greatest when glyphosate was applied to alfalfa between 8 and 10 inches tall, while yield reduction was minimized when the crop was treated before it grew four inches tall after dormancy. Lower rates of glyphosate (0.77 lb ae/acre- 22oz Roundup Powermax) generally caused less injury and yield loss compared to higher rates tested (1.54 lb ae/acre- 44oz/acre Roundup Powermax). In 2019, a multi-state researcher team evaluated this phenomenon at multiple locations in California and Utah to better determine which management practices minimize crop injury from glyphosate. Another objective was to investigate a hypothesis that the crop injury is caused by Pseudomonas syringae (bacterial stem blight).