Objectives
The objective of this study was to determine the rates at which flax tolerates sulfentrazone in different soil and climatic conditions as well as to determine rates required to provide control of broadleaf weeds such as redroot pigweed, kochia, and wild buckwheat.
Project Description
Sulfentrazone is a Group 14 herbicide that inhibits the protoporphyrinogen oxidase (PPO) enzyme, which is important in the synthesis of chlorophyll. Sulfentrazone is a soil-applied herbicide that requires soil moisture for activation and root uptake.
Tolerance and weed control efficacy studies were conducted in 2006 and 2007 at six locations across the Prairies: Lethbridge, AB; Scott, SK; Goodale farm, Saskatoon, SK; Kernen farm, Saskatoon, SK; Melfort, SK; Indian Head, SK; and Brandon, MB.
Tolerance of flax was evaluated at all locations by applying a range of sulfentrazone rates from 35 to 560 g ai/ha. Flax exhibited good tolerance to sulfentrazone at rates up to 280 g ai/ha over all sites and years. There were some locations where the highest rate (560 g ai ha) rate of sulfentrazone did not injure the crop. However, Scott, Kernen, Lethbridge, Brandon and Melfort locations had unacceptable tolerances at the high rate in at least one of the visual ratings. The only site where yields were reduced by the high rate of sulfentrazone was at Scott in both 2006 and 2007. As a 2x rate of safety is required for PMRA registration, the 1x rate will need to be lower than 280 g ai/ha.
To summarize weed control data, redroot pigweed was present in 11 site years (5 site years with 210 g ai/ha rate). Rates of 35, 70, 140, 210, 280 and 560 g ai/ha provided greater than 80% control of redroot pigweed 9%, 45%, 64%, 80%, 91% and 91% of the time, respectively. Wild buckwheat was present in ten site years (3 site years with 210 g ai/ha) and rates of 35, 70, 140, 210, 280 and 560 provided >80% control 0%, 20%, 60%, 100%, 100% and 100% of the time, respectively. Kochia was present in 7 site years (5 site years with 210 g ai/ha rate) and rates of 35, 70, 140, 210, 280 and 560 g ai/ha provided > 80% control 14%, 50%, 100%, 100%, 100% and 100% of the time, respectively.
At sites where sulfentrazone provided efficacious weed control, flax was tolerant at the rates required for weed control. In soils such as those at Scott, Lethbridge, and the Goodale and Kernen Farms, a rate of 140 g ai/ha should be adequate to control redroot pigweed, wild buckwheat, and kochia and provide a 2x rate margin of crop safety. Data generated from chickpea efficacy studies can be used to supplement the flax data and further refine rates. The high organic matter soils at Melfort are a concern since control of redroot pigweed was generally not satisfactory at any rate applied. Based on the Melfort results, further investigation in the Red River Valley of Manitoba is warranted to determine if sulfentrazone can provide efficacious weed control in flax on high organic matter, fine-textured soils.
