Sensitivity of Adzuki Bean ( Vigna angularis ) to Acifluorfen, Fomesafen, Bentazon, Imazethapyr and Halosulfuron-Methyl Applied Postemergence

New herbicide options are needed for postemergence 
(POST) broadleaf weed control in adzuki bean. A field study, of five experiments, was conducted 
over a three-year period (2014, 2015, 2016) in Ontario to evaluate the 
tolerance of adzuki bean to the POST application of acifluorfen (600 and 1200 g·ai·ha-1), fomesafen (240 and 480 g·ai·ha-1), bentazon (1080 and 2160 g·ai·ha-1), imazethapyr (100 and 200 g·ai·ha-1) and halosulfuron-methyl (75 and 150 g·ai·ha-1). 
Acifluorfen and fomesafen applied POST caused as much as 12% visible injury at 
the 1X rate and 20% visible injury at the 2X rate but had no adverse effect on 
adzuki bean population, shoot dry weight, height, maturity or yield. Bentazon 
caused as much as 23% visible injury at 1080 g·ai·ha-1 and 28% visible injury at 2160 g·ai·ha-1 but caused no adverse effect on adzuki bean population, shoot dry weight, 
height, maturity or yield at either rate, except at 2160 g·ai·ha-1 which reduced shoot dry weight 20% and height 12%. Imazethapyr caused as much 
as 22% visible injury at 100 g·ai·ha-1 and 34% visible injury at 200 g·ai·ha-1 but caused no adverse effect on adzuki bean population, shoot dry weight, 
height, maturity or yield at either rate except at 200 g·ai·ha-1 which delayed maturity slightly. Halosulfuron-methyl caused as much as 65% 
visible injury and reduced shoot dry weight, height and yield 64%, 41%, and 
28%, respectively. This research concludes that acfluorfen, fomesafen, 
bentazon, imazethapyr and halosulfuron at the rates evaluated can cause the significant injury in adzuki bean.


Introduction
Adzuki bean [Vigna angularis (Willd.)Ohwi & Ohashi] is a niche market class of bean that is popular with growers in south-western Ontario [1] [2].Most of the adzuki bean produced in Ontario is exported to Asia, in particular to Japan, where demand has been increasing steadily over the last few years [1] [2].Adzuki bean is a small, red, oval-shaped, sweet bean with a nutty taste, used mainly in sweet desserts in the orient [3].Adzuki bean is a legume crop with an indeterminate growth habit and has similar characteristics as edible dry bean (Phaseolus vulgaris L.) growing to heights of 40 -60 cm and maturing in 110 -220 days [4].Adzuki beans have slow early growth and consequently do not compete well with weeds which can cause substantial seed yield losses if not adequately controlled [4].Currently, few herbicide options are available for weed management in adzuki bean.New herbicide options must be found for the control of broadleaf weeds in adzuki bean.
nitrobenzamide} is another POST applied diphenyl ether herbicide with similar weed control spectrum as acifluorfen that is commonly used for broadleaf weed control in dry beans.Unlike acifluorfen, fomesafen has some residual activity in the soil which can help with season long control of some annual broadleaf weeds [5].Persistence in the soil is, in part, dependent on soil properties and environmental conditions [5] [6].
The purpose of this research was to ascertain the tolerance of adzuki bean to acifluorfen (600 and 1200 g•ai•ha −1 ), fomesafen (240 and 480 g•ai•ha −1 ), bentazon (1080 and 2160 g•ai•ha −1 ), imazethapyr (100 and 200 g•ai•ha −1 ) and halosulfuronmethyl (75 and 150 g•ai•ha −1 ) applied POST under Ontario environmental conditions.Herbicide treatments were applied using a CO 2 -pressurized backpack sprayer calibrated to deliver 200 L.ha −1 at 240 kPa.The boom was 1.0 m long with three ultra-low drift nozzles (ULD120-02, Hypro, New Brighton, MN) spaced 50 cm apart.All plots including the non-treated control were maintained weed free by inter-row cultivation and hand hoeing as required to eliminate the confounding effect of weed interference.Herbicides were applied 20 to 26 days after seeding when the adzuki bean was in the 1 -2 trifoliate leaf stage.

Materials and Methods
Adzuki bean injury was visually estimated on a scale of 0 (no injury) to 100% (complete plant death) at 1, 2 and 4 weeks after herbicide application (WAA).
Plant stand (population) and shoot dry weight were determined 3 WAA by counting the number of bean plants in 1 m of row, cutting them at the soil surface and drying at 60˚C to a constant moisture and then the weight was recorded.Average plant height was determined 6 WAA by measuring the height of 10 randomly selected plants per plot and recording the average.Adzuki bean was harvested at maturity with a small plot combine, weight and moisture were recorded and yields were adjusted to 14% moisture.
Data were analyzed as an RCBD using PROC MIXED in SAS 9.4 [7].Herbicide treatment was considered a fixed effect, while environment (year-location combinations), the interaction between environment and herbicide treatment, and replicate nested within environment were considered random effects.Significance of the fixed effect was tested using a F-test and random effects were tested using a Z-test of the variance estimate.The UNIVARIATE procedure was used to test data for normality and homogeneity of variance.The untreated control was excluded from the analysis for crop injury data; however, the means were compared independently to zero to evaluate which treatments differed from the untreated control.Plant stand, shoot dry weight, height and yield were converted to a percent of the untreated control for analysis.Shoot dry weight and seed moisture content were log transformed to satisfy the variance analysis assumptions.Treatment comparisons were made using Fisher's Protected LSD at P < 0.05.Data compared on the transformed scale were back transformed for presentation.

Results and Discussion
Statistical analysis of the data on visible adzuki bean injury, plant population, shoot dry weight, plant height, seed moisture content (maturity) and seed yield showed that the random effects of location, year, year by location and interactions with treatments was not significant.Therefore, data were pooled and averaged over years and locations (Table 1).

Acifluorfen
Acifluorfen, applied POST, caused 12%, 12% and 5% visible injury at 600 g•ai•ha −1 and 20%, 20% and 12% visible injury at 1200 g•ai•ha −1 evaluated 1, 2 and 4 WAA, respectively (Table 1).There was no effect of acifluorfen, applied POST at 600 and 1200 g•ai•ha −1 , on adzuki bean population, shoot dry weight, height, maturity or seed yield (Table 1).Results are similar to those reported by Stewart et al. [8] who found up to 7% visible injury in adzuki bean with no adverse effect on plant height or seed yield when treated with acifluorfen applied POST at 600 or 1200 g•ai•ha −1 .

Fomesafen
Fomesafen, applied POST, caused 9%, 8% and 4% visible injury at 240 g•ai•ha −1 and 18%, 17% and 10% visible injury at 480 g•ai•ha −1 evaluated 1, 2 and 4 WAA, respectively (Table 1).Fomesafen, applied POST at 240 and 480 g•ai•ha −1 , caused no adverse effect on adzuki bean population, shoot dry weight, height, maturity or seed yield (Table 1).The results from this study are similar to Powell et al. [9] who found 14% to 28% injury in adzuki bean with no adverse effect on final seed yield and Stewart et al. [8] who found 8% visible injury in adzuki bean with no adverse effect on plant height or seed yield of adzuki bean with fomesafen applied POST at 240 or 480 g•ai•ha −1 .In studies with Phaseolus vulgaris such as black and cranberry bean, injury was minimal and transient with fomesafen applied POST at 240 or 480 g•ai•ha −1 alone or tankmixed with other herbicides [10].

Bentazon
Bentazon, applied POST, caused 19%, 23% and 20% visible injury at 1080 g•ai•ha −1 and 25%, 28% and 28% visible injury at 2160 g•ai•ha −1 evaluated 1, 2 and 4 WAA, respectively (Table 1).Bentazon, applied POST at 2160 g•ai•ha −1 , did not adversely affect adzuki bean shoot dry weight and height, but at 2160 g•ai•ha −1 , it reduced shoot dry weight 20% and height 12% compared to the untreated control (Table 1).Adzuki bean population, seed moisture content and seed yield were not adversely affected by either rate of bentazon (Table 1).In other studies, bentazon caused higher injury in adzuki bean.Stewart et al. [8] found that bentazon applied POST at 1080 or 2160 g•ai•ha −1 caused as much as 66% visible injury and reduced biomass 90%; height 27% and seed yield 57% in adzuki bean.Effect of bentazon on Phaseolus vulgaris species has been variable.VanGessel et al. [11] found that bentazon applied POST caused as much as 20% visible injury in dry bean but Soltani et al. [10] found less than 3% injury in dry bean.Also, Wall [12] found 21% seed yield reductions in dry bean but Blackshaw et al. [13] and Burnside et al. [14] found no seed yield reduction with bentazon applied POST in dry bean.

Imazethapyr
Imazethapyr, applied POST, caused 22%, 21% and 15% visible injury at 100 g•ai•ha −1 and 31%, 34% and 27% visible injury at 200 g•ai•ha −1 evaluated 1, 2 and 4 WAA, respectively (Table 1).Imazethapyr applied POST at 100 and 200 g•ai•ha −1 had no adverse effect on adzuki bean population, shoot dry weight, height, seed moisture content or seed yield except for seed moisture content which was increased 0.9% at 200 g•ai•ha −1 compared to the untreated control indicating that adzuki bean injury from imazethapyr delayed maturity (Table 1).Results are similar to those found by Stewart et al. [8] who reported as much as 23% visible injury in adzuki bean with no adverse effect on plant height or seed yield of adzuki bean with imazethapyr applied POST at 100 or 200 g•ai•ha −1 .However, Powell et al. [9] found 4% injury in adzuki bean with no adverse effect on final seed yield with imazethapyr.

Conclusion
Results from this research show that acifluorfen (600 and 1200 g•ai•ha −1 ), fomesafen (240 and 480 g•ai•ha −1 ), bentazon (1080 and 2160 g•ai•ha −1 ), imazethapyr (100 and 200 g•ai•ha −1 ) and halosulfuron (75 and 150 g•ai•ha −1 ) applied POST cause the significant injury in adzuki bean.Injury with acifluorfen and fomesafen was not as severe and persistent as bentazon, imazethapyr or halosulfuronmethyl.Further studies are needed to determine if lower rates of these herbicides will result in less visible injury but still provide the effective control of annual broadleaf weeds in adzuki bean under Ontario environmental conditions.

Five
field experiments were conducted in southwestern Ontario over a threeyear period (1 in 2014, 2 in 2015 and 2 in 2016).Locations included the University of Guelph, Huron Research Station, Exeter, ON (2014, 2015 and 2016) and University of Guelph, Ridgetown Campus, Ridgetown, ON (2015 and 2016).The soil at the Exeter location was a Brookston clay loam and at Ridgetown was a Brookston loam soil.Seedbed preparation included moldboard plowing in the fall followed by two passes with a field cultivator with rolling basket harrows in the spring prior to seeding adzuki bean.The field experiments were arranged in a randomized block design with treatments replicated four times.Treatments consisted of a non-treated control, acifluorfen at 600 and 1200 g•ai•ha −1 , fomesafen at 240 and 480 g•ai•ha −1 (plus a nonionic surfactant at 0.25 v/v), bentazon at 1080 and 2160 g•ai•ha −1 , imazethapyr at 100 and 200 g•ai•ha −1 (plus a nonionic surfactant at 0.25 v/v and 2 L.ha −1 of 28% urea ammonium nitrate) and halosulfuron-methyl at 75 and 150 g•ai•ha −1 (plus a nonionic surfactant at 0.25 v/v) representing once and twice the maximum labelled use dose in dry bean or soybean in Ontario.Each plot was 1.5 m wide and consisted of two rows of "Erimo" adzuki bean, spaced 0.75 m apart in rows that were 10 m long at Exeter and 8 m long at Ridgetown.Adzuki bean was seeded in early June at a rate of 175,000 seeds ha −1 .

Table 1 .
Percent visible adzuki bean injury 1, 2 and 4 WAA, plant stand, dry weight, height, seed moisture content (maturity) at harvest and yield (as percent of untreated control) for adzuki bean treated with various POST herbicides at Exeter and Ridgetown, ON from 2014 to 2016.Means followed by a different letter within a column are significantly different according to Fisher's Protected LSD at P < 0.05.a a Plant stand, dry weights, height and yield analyzed as a percent of the untreated check.Abbreviations: POST, postemergence; WAA, weeks after herbicide application.b Included non-ionic surfactant at 0.25% v/v.c Included 28% UAN at 2 L ha −1 .