Metribuzin is tough on chickpeas
Two weeks after metribuzin treatment, chickpea mortality was 25% at the full label rate, and 56% for the 2X rate. Accumulated chlorosis and necrosis were similar for the control and 1/2X rate. The 1X rate significantly reduced pod production by 75% and was similar to the pod reduction after three weeks of water stress (90%).
An emerging plant health issue developed on chickpea in Saskatchewan in 2019. Following rainfall events around flowering to early podding, apical wilting and chlorosis affected secondary growth on the main branches. Additional symptoms included chlorosis and necrosis of leaf margins and white spots on the leaves. These symptoms occasionally occurred with rainfall following drought stress.
One of the factors that was considered was whether the application of metribuzin could be contributing to the plant health issue. A greenhouse study at the Saskatoon Research and Development Centre, AAFC was conducted to evaluate the effect of metribuzin dose and short-term water stress on chickpea health, growth and pod production.
Metribuzin was applied at 4 rates of 0, 103, 206, and 413 g ai/ha. The full dose label rate is 206 g ai/ha. Metribuzin was applied when plants reached the 1- to 3- aboveground node stage according to label recommendation. Chickpea was 2.4 inches (6 cm) tall and had 2 compound leaves.
CDC Leader chickpea was planted for the first run on Nov 24, 2021 with water stress treatment running from Dec 29, 2021 to January 24, 2022 with one watering on January 13, 2022. The second run was planted March 21, 2022 with water stress from April 26 to May 17, 2022, with supplemental watering on April 29 and May 6.
Data collected included wilting, accumulated chlorosis and necrosis, longest branch length, pod number at harvest, and the leaf area at harvest.
Twenty-five per cent mortality
Measured at 2 weeks after treatment, the 1X metribuzin label rate caused 25% chickpea mortality and the 2X label rate caused 56% chickpea mortality.
At the 1/2X rate, accumulated chlorosis and necrosis was measured at 21%, and was similar to the control at 15%. However, the label rate caused increased necrosis measured at 56% and the 2X rate caused 73% necrosis.
Measurements at 4 weeks after treatment (WAT) found the lowest accumulated chlorosis and necrosis at 36%, which was similar to 1 WAT at 42% and 2 WAT at 37%. However, measurements at 6 WAT (45%) and 8 WAT (49%) indicates that chickpea recovery from metribuzin application had occurred by 4 WAT and then was followed by increased necrosis at later growth stages.
Drought stress did not affect accumulated chlorosis and necrosis.
Chickpea pod production was reduced by 75% with the label metribuzin rate and 90% with the water stress regime.
Effect of metribuzin dose and irrigation regime on chickpea pod production while grown in a greenhouse in Saskatoon, SK in 2021–2022
Source: Sharpe et al. 2024
Overall, the labelled rate of metribuzin or drought significantly and negatively affected chickpea plant health, but the half-dose rate often used by chickpea growers caused mild symptoms. However, the risk of herbicide-resistance developing in weeds when the one-half rate is used is a concern. This greenhouse research highlighted the impact of metribuzin and drought on chickpea health, but neither were consistent with the emerging chickpea health issue in Saskatchewan.
Research funding was provided by the Saskatchewan Pulse Crop Development Board and the Saskatchewan Ministry of Agriculture.
Shaun M. Sharpe, Jeff Schoenau, Michelle Hubbard, Impact of metribuzin dose and water stress on chickpea plant health, Crop Protection, Volume 174, 2023, 106391, OPEN ACCESS https://doi.org/10.1016/j.cropro.2023.106391
Photo by Shaun Sharpe. Leaf margin chlorosis on chickpea caused by metribuzin one week after application.
