Weed Management in White Bean with Variable Doses of S -Metolachlor and Halosulfuron Applied Preemergence

Five experiments were conducted in Ontario, Canada from 2016 to 2018 to determine how doses of S-metolachlor and halosulfuron applied preemergence (PRE) should be adjusted to control specific weed species in white bean. S-metolachlor, halosulfuron, and S-metolachlor + halosulfuron caused minimal (1% to 4%) injury in white bean. Weed interference reduced white bean yield 54%. On average, weed interference with S-metolachlor and halosulfuron decreased yield 34% and 29%, respectively. In contrast, white bean seed yield was similar to the weed-free control with the S-metolachlor + halosulfuron tankmixes. S-metolachlor applied alone controlled A. theophrasti, A. retroflexus, A. artemisiifolia, C. album, E. crus-galli and S. viridis 0% to 3%, 78% to 93%, 0% to 9%, 5% to 15%, 97% to 99% and 96% to 98%, respectively. Halosulfuron applied alone controlled A. theophrasti, A. retroflexus, A. artemisiifolia, C. album, E. crus-galli and S. viridis 39% to 87%, 93% to 99%, 64% to 88%, 34% to 59%, 10% to 30% and 13% to 35%, respectively. S-meto-lachlor + halosulfuron tankmixes controlled A. theophrasti, A. retroflexus, A. artemisiifolia, C. album, E. crus-galli and S. viridis 47% to 94%, 98% to 100%, 78% to 94%, 37% to 78%, 94% to 98% and 91% to 96%, respectively. Weed density and biomass reductions with the herbicides evaluated followed the same pattern as visible weed control assessments. Results from this study in-dicate that doses of S-metolachlor and halosulfuron, when applied as a tankmix, should be adjusted based on a weed species composition in each indi-vidual white bean field.


Introduction
Dry bean (Phaseolus vulgaris L.) is popular legume crop grown in Ontario. Approximately 80% -90% of dry bean harvested in Ontario is exported out of the province [1]. White bean has been produced in the province since the early 1900's and over the years has become the most popular dry bean market class grown [1]. In 2018, approximately 63,000 tonnes of white beans were produced from 22,000 ha in Ontario with a value of nearly $49 million [2]. Controlling weeds is one of the most important concerns for white bean production in On-  [3]. These problematic weeds generally germinate early in the season and are fast growing thereby outcompeting the slower growing white bean plants for irradiance, moisture and nutrients resulting in substantial yield losses [4]. White bean seed yield losses have been reported to be 68% to 81% in white bean from weed interference [5]- [12]. There are currently few herbicide choices that producers can choose from to control these problematic weed species in white bean.
Halosulfuron is a recently registered sulfonyl-urea herbicide for broadleaved weed control in white bean in Ontario (OMAFRA 2018). Major weeds controlled with halosulfuron includes A. theophrasti, C. album, S. arvensis, P. persicaria, A. retroflexus and X. strumarium, including biotypes that are resistant to Group 5 (triazine) herbicides [13] [14]. There is little activity with halosulfuron against grass weed species at doses registered in white bean (OMAFRA 2018). Therefore, halosulfuron needs to be used along with a graminicide to provide broadspectrum control of problematic weeds in white bean [3].
S-metolachlor (the active of isomer of metolachlor) is a chloroacetanilide herbicide that is registered in white bean to control of key weeds in Ontario including Echinochloa spp., Setaria spp., Panicum spp., Digitaria spp., Solanum spp. and Amaranthus spp. [15]. S-metolachlor tank mixed with halosulfuron can control troublesome grass and broadleaved weeds (including Group 5 resistant biotypes) in white bean. The S-metolachlor label has a dose range of 1050 to 1600 g•ai•ha −1 and the halosulfuron label has a dose range of 25 to 50 g•ai•ha −1. Earlier research has primarily focused on halosulfuron at 35 g•ai•ha −1 for weed control in white bean [6] [9] [10] [16]. Limited information exists on the effect of S-metolachlor plus lower doses of halosulfuron particularly at the lowest labelled dose of 25 g•ai•ha − The purpose of this research was to evaluate how doses of S-metolachlor and halosulfuron should be adjusted to control specific problematic weeds in white bean production.

Materials and Methods
Field experiments (total of 5) were established at the University of Guelph Re- The GLIMMIX procedure in SAS [17] was used to analyze the data. In the analysis, herbicide treatment was the fixed effect and environment (year-location combinations), replicate within the environment and the environment-treatment interaction were the random effects. The best distribution and associated link function for each parameter was chosen by comparing fit statistics, residual plots and the Shapiro-Wilk statistic among the potential distributions. LSMEANS were calculated by using the inverse link function, and pairwise comparisons were subjected to Tukey's adjustment before determining treatment differences at P < 0.05. The Gaussian distribution and identity link were used for percent visible white bean injury 2 and 4 WAE, percent visible weed control of A. theophrasti and C. album 8 WAE, E. crus-galli dry weight and white bean yield.
Percent visible weed control of all remaining weed species at 2 and 4 WAE were analyzed using arcsine square root distribution and identity link. Weed density and weed shoot dry weight were analyzed using the lognormal distribution and identity link. The weedy control (assigned a value of 0 for injury and weed control) and weed-free control (assigned a value of 0 for injury, weed density and biomass, or 100 for weed control) were excluded from the analysis due to zero variance. Comparisons were still possible between the other treatments and the value zero using the LSMEANS output and differences were identified. Arcsine square root and lognormal distributions were back-transformed for presentation of results.

White Bean Injury and Yield
Visible white bean injury from the herbicides evaluated was minimal. S-metolachlor, halosulfuron, and S-metolachlor + halosulfuron, applied PRE, caused < 5% injury in white bean 2 and 4 WAE ( Weed interference delayed maturity (as indicated by seed moisture content at harvest) and reduced white bean seed yield 54%. Interference from weeds with

Weed Control
Weeds selected for analysis needed to be present in at least 2 out of the 5 environments. Major weed species present on study sites included A. theophrasti, A. retroflexus, C. album, A. artemisiifolia, E. crus-galli and S. viridis.

Chenopodium album
S-metolachlor applied alone at the doses evaluated provided poor (5% to 15%) control of C. album (Table 5). Halosulfuron alone at doses evaluated controlled C. album only 34% to 59%. S-metolachlor + halosulfuron at doses evaluated also provided less than adequate control (37% to 78%) of C. album. Increasing the Table 4. Percent visible control 4 and 8 WAE, density and dry weight of Ambrosia artemisiifolia treated with S-metolachlor and halosulfuron applied PRE at Exeter (2017) and Ridgetown (2016-2018) a,b .  dose of S-metolachlor or halosulfuron did not significantly increase the control of C. album. S-metolachlor, halosulfuron, and S-metolachlor + halosulfuron reduced C. album density as much as 73%, 94% and 97%, respectively. However, shoot weight was not different than the weedy control with all herbicide treatments except for S-metolachlor (1600 g•ai•ha −1 ) + halosulfuron at 37.5 and 50 g•ai•ha −1 which reduced C. album dry weight 86% and 85%, respectively (Table 5).
Halosolfuron alone at doses evaluated did not reduce S. viridis density or dry weight (Table 7). However, S-metolachlor and S-metolachlor + halosulfuron reduced S. viridis density as much as 89% and 86% and S. viridis dry weight as much as 94% and 93%, respectively (Table 7).
For fields with A. theophrasti, there was a trend for improved control with the higher doses of halosulfuron. For fields with A. artemisiifolia, there was a trend for improved control with the higher doses of halosulfuron when applied as a tankmix with the low dose of S-metolachlor, however, there was no need to increase the halosulfuron dose when applied as a tankmix with the high dose of S-metolachlor. For fields with A. retroflexus species, E. crus-galli and S. viridis, a tankmix of S-metolachlor + halosulfuron at the low dose was sufficient to provide excellent weed control. Using this information, white bean producers can maximize crop yield and reduce input costs while reducing unnecessary loading of herbicides into the environment by adjusting herbicide doses depending on weed species present in their land.