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Control of Biennial Wormwood in Dry Bean
April 15, 2002

By George O. Kegode, Department of Plant Sciences, North Dakota State University and Brian M. Jenks, North Central Research and Extension Center, Minot, N.D.

Biennial wormwood is now considered an established weed in many copping systems in North Dakota, Minnesota, and South Dakota. However, a majority of the biennial wormwood populations have been associated more with dry bean and soybean production systems. Biennial wormwood first appeared in these cropping systems in the early 1990s but was routinely misidentified as common ragweed. Consequently, herbicides that were applied to treat these infestations did not adequately control biennial wormwood. Research was conducted in 2000 and repeated in 2001 to identify the best control options for biennial wormwood control in dry bean using registered and experimental herbicides. Results presented are for research conducted in 2001.

A study was conducted on a site that had a history of biennial wormwood infestation at the North Central Research Extension Center farm, Minot, ND over the summer of 2001. The study was initiated on June 2 with the application of preplant incorporated (PPI) herbicides. "Maverick" pinto bean was seeded on June 2 at 60 lb/A. Preemergence (PRE) treatments were applied on June 2 and postemergence treatments were applied on July 9 (POST) and July 23 (POST 2). Control of biennial wormwood as well as kochia, because of high populations of both species, was evaluated on July 5 and August 15. The study included Spartan, Valor, Python, Broadstrike + Dual, and Raptor that were not registered for use in dry beans as of late 2001.

With the exception of Treflan, all treatments provided fair to excellent control of biennial wormwood. Increasing the rate of Spartan from 2.67 to 10.66 oz/A resulted in increased biennial wormwood control at the August 15 evaluation (Table 1). However, due to differences in soil pH among replicates at the study site, whereby the first replicate had higher soil pH, Spartan caused significant injury to dry bean that that resulted in lower yields (Table 2). In comparison, the second and third replicates had lower soil pH and, consequently, there was less injury to dry bean. Sencor and Valor also provided good to excellent control of biennial wormwood (Table 1) and also caused significant injury to dry bean that probably was related to soil pH (Table 2). Basagran, Broadstrike + Dual, and Python provided good to excellent control of biennial wormwood and no injury to dry bean.

Spartan, Sencor, Valor, and Basagran provided good to excellent kochia control. Despite having provided excellent control of biennial wormwood, Broadstrike + Dual, Python, and Treflan provided little or control of kochia (Table 1) therefore, follow up herbicide applications would be necessary where biennial wormwood and kochia both are problematic. The higher use rates of Spartan as well as Sencor at 0.33 lb/A gave excellent control of both weed species but producers need to be wary of potential dry bean injury from these herbicides if soil pH is high.


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