American Journal of Plant Sciences, 2011, 2, 835-840 doi:10.4236/ajps.2011.26098 Published Online December 2011 (http://www.SciRP.org/journal/ajps) Copyright © 2011 SciRes. AJPS 835 Response of Eight Market Classes of Dry Bean (Phaseolus vulgaris L.) to Pendimethalin Nader Soltani 1* , Robert E. Nurse 2 , Christy Shropshire 1 , Peter H. Sikkema 1 1 University of Guelph Ridgetown Campus, Ridgetown, Canada; 2 Agriculture and Agri-Food Canada, Harrow, Canada. Email: * nsoltani@ridgetownc.uoguelph.ca Received October 5 th , 2010; revised November 8 th , 2011; accepted November 20 th , 2011. ABSTRACT There is little information on the tolerance of dry bean to pendimethalin. Field studies were conducted in 2007 to 2009 at Exeter, Ontario and in 2008 and 2009 at Ridgetown, Ontario to evaluate tolerance of black, cranberry, kidney, otebo, pink, pinto, Small Red Mexican (SRM) and white bean to pendimethalin applied preplant incorporated (PPI) at 1080 and 2160 g·a.i·ha –1 . Pendimethalin PPI caused minimal injury in most market classes of dry bean at 1 and 2 weeks after emergence (WAE). There was no injury in various market classes of dry bean with the low dose at 1 and 2 WAE. However, at the high dose there was 0 to 4% injury at 1 WAE and 0 to 7% injury at 2 WAE in black, cranberry, kidney, otebo, pink, pinto, SRM and white bean. Pendimethalin PPI was more injurious in white bean than in black, cranberry, kidney, otebo, pink, pinto and SRM bean. Pink and SRM bean exhibited the most tolerance to pendimethalin applied PPI at 1080 g·ai·ha –1 or 2160 g·ai·ha –1 . Pendimethalin caused no adverse effect on plant height, shoot dry weight, seed moisture content and seed yield of black, cranberry, kidney, otebo, pink, pinto, SRM and white bean. Based on these results, there is an adequate margin of crop safety for pendimethalin applied PPI at the proposed dose of 1080 g·ai·ha –1 in black, cranberry, kidney, otebo, pink, pinto, SRM and white bean in Ontario. Keywords: Black Bean, Cranberry Bean, Kidney Bean, Otebo Bean, Pendimethalin, Pink Bean, Small Red Mexican Bean, Phaseolus vulgaris L., White Bean 1. Introduction Dry bean (Phaseolus vulgaris L.) is an important crop grown in southern Ontario since the 1940’s [1]. The Ontario white bean and Ontario coloured bean industry include about 1000 growers that plant approximately 95,000 ha and produce approximately 77,000 MT of dry bean with annual farm-gate value of about $70,000,000 [2]. Dry bean is an alternative high-value crop that producers can grow in rotation with wheat (Triticum aestivum L.), field corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] in southwestern Ontario. Major market classes (same geographic origin, gene pool, seed size and seed color) of dry bean grown in Ontario include black, cranberry, kidney and white (navy) bean. In recent years other speciality market classes of dry beans such as otebo, pink, pinto and Small Red Mexican (SRM) bean are also produced as farmers diversify their production and pursue new global markets, especially those in Asia. Weed control is one of the most critical problems facing growers as dry bean is a poor competitor with weeds. Weeds compete with dry bean for moisture, nutrients and light and can cause significant seed yield and seed quality losses if not adequately controlled [3-7]. Ontario dry bean producers have a limited number of herbicide op- tions available to them for grass and broadleaf weed control. More research is needed to identify herbicides that provide consistent annual grass and broadleaf weed control and are safe to use on dry bean. Pendimethalin is a dinitroaniline selective herbicide used to control most annual grasses and certain broadleaf weeds in field corn, soybean, rice, potatoes, lettuce, stone fruit, cotton, peanuts, sunflowers and berry fruits in- cluding strawberry [8]. Pendimethalin is primarily ab- sorbed by root. It inhibits cell division and cell elon- gation. Susceptible plants die shortly after germination or following emergence from the soil [8]. Pendimethalin can be used preplant incorporated (PPI), preemergence (PRE), and early postemergence (EPOST) [8,9]. Pendi- methalin controls annual grasses such as barnyardgrass (Echinochloa crusgalli (L.) Beauv.), smooth crabgrass (Digitaria ischaemum (Schreb) Muhl.), large crabgrass (Digitaria sanguinalis (L.) Scop), fall panicum (Panicum dichotomiflorum Michx.), giant foxtail (Setaria faberii