Efficacy of Trifluralin Compared to Ethalfluralin Applied Alone and Co-Applied with Halosulfuron for Weed Management in White Bean

There are a limited number of herbicides registered for weed management in white bean production in Ontario, Canada. Five field experiments were com-pleted in Ontario from 2016 to 2018 to compare the efficacy of trifluralin and ethalfluralin applied alone and in combination with halosulfuron, applied preplant incorporated (PPI), for weed control efficacy and white bean tolerance and seed yield. At 2 and 4 WAE, there was no white bean injury from the herbicide treatments evaluated. Trifluralin applied PPI provided up to 32%, 99%, 13%, 99%, 27%, 99% and 99% control of velvetleaf, redroot pigweed, common ragweed, common lambsquarters, wild mustard, barnyardgrass and green foxtail, respectively. Trifluralin and ethalfluralin provide similar control of velvetleaf, redroot pigweed, barnyardgrass and green foxtail control, however, ethalfluralin is slightly more efficacious on common ragweed, common lambsquarters and wild mustard. Halosulfuron (35 g∙ai∙ha −1 ), applied PPI, provided as much as 76%, 98%, 96%, 96%, 100%, 19% and 23% control of velvetleaf, redroot pigweed, common ragweed, common lambsquarters, wild mustard, barnyardgrass and green foxtail, respectively. Trifluralin (600 or 1155 g∙ai∙ha −1 ) + halosulfuron (35 g∙ai∙ha −1 ), applied PPI, provided up to 88%, 100%, 98%, control. Trifluralin or ethalfluralin co-applied with halosulfuron can be safely used in white bean production for the control of common annual grass and broadleaf weeds in Ontario.


Introduction
Canada is one of the major dry bean (Phaseolus vulgaris L.) producing countries in the world [1]. White (navy) bean is the largest market class of dry bean grown in Canada [2]. Most of the white bean produced in Canada is grown in Ontario.
On an annual basis, white bean growers in Ontario harvest approximately 26,000 hectares and produce 58,000 tonnes of white bean with a farm gate value of $36,000,000 [2]. Weeds management is a critical component of successful white bean production as weed interference can reduce seed yield as much as 81% [1] [3] [4] [5] [6]. There are a limited number of herbicides registered for weed management in white bean production in Ontario [7]. New herbicides/tank mixes are needed to effectively control common annual grass and broadleaf weeds in white bean production.
aniline] is a Group 3 dinitroanaline herbicide that can control/suppress problematic grassy weeds such as barnyardgrass (Echinochloa crusgalli (L.) Beauv.), green foxtail (Setaria viridis L.), yellow foxtail (Setaria pumila L.), volunteer barley (Hordeum vulgare L.), volunteer wheat (Triticum aestivum L.) and wild oats (Avena sativa L.) [9] [10]. Ethalfluralin can also control/suppress broadleaf weeds such as kochia (Bassia scoparia subsp. densiflora), wild buckwheat (Polvgonum convolvulus L.), redroot pigweed and common lambsquarters [10] [11]. Ethalfluralin, a Group 3 herbicide, can be one component of a di-  [12]. Halosulfuron has been recently registered at 25 to 50 g•ai•ai•ha −1 for use in white bean production [7]. Ethalfluralin is not currently registered for use in any market class of dry bean in Ontario. Ethalfluralin has been reported to be a more active herbicide than trifluralin [10]. Ethalfluralin and trifluralin co-applied with halosulfuron can provide effective broad-spectrum control of common annual grass and broadleaf weeds in white bean production in Ontario. However, limited information is available on comparing the efficacy of trifluralin and ethalfluralin applied alone and in combination with halosulfuron for weed management in white bean under Ontario environmental conditions. The purpose of this study was to compare the efficacy of trifluralin and ethalfluralin applied alone and in combination with halosulfuron, applied PPI, on white bean tolerance and yield, and weed control efficacy.  Tables 1-8. The experimental plots were 3.0 m wide and 8 or 10 m long depending on lacation. White bean "T9905" was seeded approximately 4 cm deep at the rate of approximately 250,000 seeds ha −1 in rows that were spaced 75 cm apart in late May to early June.

Experimental Methods
Herbicides treatments were applied 1 -2 days before seeding and incorporated within one day with two passes of a field cultivator with rolling basket harrows in opposite directions. Herbicides were applied with a CO 2 -pressurized backpack sprayer calibrated to deliver 200 L•ha −1 at 240 kPa. The spray boom was 1.5 m       White bean yield was determined by harvesting the middle two rows of each plot with a plot combine at maturity. White bean yield was adjusted to 18% seed moisture content.

Statistical Analyses
The GLIMMIX procedure in SAS [13] was utilized for data analysis, with herbi-

Crop Injury
At 2, 4 and 8 WAE, there was no white bean injury from the herbicide treatments evaluated (data not presented). There was a delay in white bean maturity due to weed interference as indicated by increased seed moisture content at harvest (Table 1). Weeds interference decreased white bean seed yield 72% (Table 1). Generally, white bean yield reflected the level of weed control provided by the herbicide treatments evaluated. There was no difference in white bean seed yield between trifluralin and ethalfluralin. Weed presence decreased seed yield 44% -45% with trifluralin and 30% -41% with ethalfluralin (Table 1).
Weed interference with halosulfuron applied alone decreased seed yield 34% (Table 1). In contrast, decreased weed interference with trifluralin and ethalfluralin applied in combination with halosulfuron resulted in white bean seed yield that was similar to the weed-free control.

Conclusions
Trifluralin and ethalfluralin applied PPI alone or in combination with halosulfuron caused no visible injury in white bean at rates evaluated. There was delayed white bean maturity due to weed interference as indicated by increased seed moisture content at harvest. Weeds presence decreased white bean seed yield 72%. Generally, white bean yield reflected the level of weed control provided by the herbicide treatments evaluated. There was no difference in white bean seed yield between trifluralin and ethalfluralin. Decreased weed interference with trifluralin and ethalfluralin applied in combination with halosulfuron resulted in white bean seed yield that was similar to the weed-free control. Trifluralin and ethalfluralin applied PPI alone did not provide adequate control of velvetleaf, common ragweed and wild mustard, but provided good to excellent control of redroot pigweed, common lambsquarters, barnyardgrass and green foxtail. Trifluralin and ethalfluralin provide similar control of velvetleaf, redroot pigweed, barnyardgrass and green foxtail control, however, ethalfluralin is slightly more efficacious on common ragweed, common lambsquarters and wild mustard. Halosulfuron applied PPI alone provided inadequate control of barnyardgrass and green foxtail, fair control of velvetleaf and good to excellent control of redroot pigweed, common ragweed, common lambsquarters and wild mustard. Trifluralin and ethalfluralin applied PPI in combination with halosulfuron provided good to excellent control of velvetleaf, redroot pigweed, common ragweed, common lambsquarters, wild mustard, barnyardgrass and green foxtail. This study concludes that trifluralin or ethalfluralin co-applied with halosulfuron can be safely used for broad-spectrum control of annual grass and broadleaf weeds in white bean production in Ontario.