Tolerance of cranberry (Vaccinium macrocarpon Ait.) at different phenological stages to the postemergent broadleaf herbicide clopyralid (0.21 or 0.42 kg a.i./ha) was evaluated in Washington, New Jersey, Massachusetts, and Wisconsin. Tolerance varied among states, rates, and application times. Applications made during early shoot growth, especially at the high rate, usually resulted in the most crop injury (leaf cupping and epinasty and reduced yield); while applications at the low rate made after vegetative development occurred usually resulted in less or no injury. No phytotoxicity occurred when applications were made before shoot growth (Washington and New Jersey). Chemical name used: 3,6-dichloro-2-pyridinecarboxylic acid (clopyralid).
), black medic ( Medicago lupulina ), and cutleaf evening-primrose ( Oenothera laciniata ) can survive fumigant treatment and become mid- to late-season problems ( Mossler, 2010 ; Stall, 2008 ). Clopyralid has previously been shown to be a potential
both experiments, five different rates of glyphosate (Roundup Weathermax; Monsanto Company, St. Louis, MO), dicamba (Clarity; BASF Corp., Durham, NC), clopyralid (Stinger; Dow AgroSciences, Indianapolis, IN), quinclorac (Facet L and Facet 75 DF, BASF
to minimize damage to other desirable vegetation ( Bradley and Hagood, 2002 ; Senseman, 2007 ). Picloram and clopyralid belong to the pyridine family of herbicide mimics of indole-3-acetic acid. Picloram is labeled for broadleaf weed control in
Resistance to the auxin-like herbicide picloram has been reported in a yellow starthistle population growing in Washington. In addition, this population is cross resistant to clopyralid, another auxin-like herbicide. To understand the mechanism of resistance to clopyralid, studies were was conducted to determine uptake and translocation and to characterize clopyralid-induced ethylene production in the susceptible (S) and resistant (R) biotypes. R and S yellow starthistle plants were grown under ambient greenhouse conditions until full rosette stage and then transferred to a growth chamber (14-hour photoperiod, 25°C, 200 mol·m–2·s–1) 48 hours before treatment. Radiolabel solutions were prepared from 12C and 14C-clopyralid. Each treatment in the uptake experiment contained 0.009 Ci (20,000 dpm) and in the translocation experiment 0.225 Ci (500,000 dpm). Clopyralid 11.7 mm (420 g a.e./ha) solutions were applied as six 0.5-L droplets to the adaxial surface of completely expanded leaves using a microsyringe. Radioactivity was quantified by Liquid Scintillation Spectrometry. Uptake was determined at specified times after treatment. Almost all clopyralid uptake occurred within the first 2 hours, with no significant differences between the two biotypes. The amount of picloram translocated was 2.4%, 40.2%, and 50.7% of that absorbed at 2, 24, and 96 hours after treatment, respectively, but was not different between biotypes. Clopyralid induced about ten times greater ethylene production in S than in R. Ethylene production was followed by epinasty and chlorosis but appears to play only a small role in the resistance mechanism.
Broadleaf weed control with trifluralin, oxyfluorfen, pendimethalin, clopyralid, pyridate, and metolachlor in cabbage (Brassica oleracea L.) grown for seed was evaluated. No single herbicide controlled broadleaf weeds adequately, with the exception of pendimethalin at 1.92 and 3.84 kg a.i./ha. However, combinations of trifluralin + oxyfluorfen, pendimethalin + clopyralid, and oxyfluorfen + pyridate effectively controlled weeds and did not reduce seed yields. Herbicides caused slight to moderate injury symptoms to cabbage plants, with the greatest injury caused by pendimethalin and the least by trifluralin and metolachlor. However, plants recovered from these symptoms and appeared normal at the bud stage. None of the herbicides applied alone or in combinations adversely affected cabbage population, height, or flowering date. Chemical names used: 3,6-dichloro-2-pyridinecarboxylic acid (clopyralid); 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide (metolachlor); 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene (oxyfluorfen); N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin); O-(6-chloro-3-phenyl-4-pyridazin-yl)S-octylcarbonothioate (pyridate); 2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine (trifluralin).
With increasing pressure to reduce disposal of yard waste in landfills, many homeowners are seeking alternative methods for grass clipping disposal. When turf is treated with pesticides, the collected grass clippings become a potential source of injury to susceptible plants that come in contact with the clippings. In this study, grass clippings were collected at 2, 7, and 14 days after pesticide treatment from a turf treated with chlorpyrifos, clopyralid, 2,4-D, flurprimidol, isoxaben, or triclopyr. The clippings were used as a mulch around Lycopersicon esculentum Mill. (tomato), Phaseolus vulgaris L. (bush bean), Petunia ×hybrida Hort. Vilm.-Andr. (petunia), and Impatiens wallerana Hook. f. (impatiens). Beans were planted 4 weeks prior to mulching, whereas the other plants were grown in the greenhouse for 6 weeks and transplanted into the field 2 weeks prior to mulching. Clippings containing residues of clopyralid, 2,4-D, or triclopyr killed tomato, bean, and petunia plants when used 2 days after pesticide treatment (DAPT) and severely injured these same species when mulched 7 and 14 DAPT. Flurprimidol injured tomato, impatiens, and bean plants when present on mulch collected 2, 7, and 14 DAPT, but was not lethal. Flurprimidol slowed plant growth, caused darker green leaf color, and reduced flowering when mulched at 2 DAPT. Isoxaben injured tomato and bean plants when present on mulch used 2, 7, and 14 DAPT but was not lethal. Injury was not as severe in the second year of the study, indicating different environmental stresses and climatic conditions make predicting pesticide injury for all growing seasons difficult; however, grass clippings from a turf treated with herbicides or plant growth regulators should not be used for mulch around sensitive plants for at least 14 DAPT. Chemical names used: 0,0-diethyl O-(3,5,6-trichloro-2-pyridinyl) phosphorothioate (chlorpyrifos); 3,6-dichloro-2-pyridinecarboxylic acid, triethylamine salt (clopyralid); 2,4-dichlorophenoxyacetic acid, dimethylamine salt (2,4-D); α-(1-methylethyl)-α-[4-(trifluromethoxy)phenyl]-5-pyrimidinemethanol (flurprimidol); N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyl]-2,6-dimethoxybenzamide and isomers (isoxaben); 3,5,6-trichloro-2-pyridinyloxy acetic acid, triethylamine salt (triclopyr).
Hagood, 2002a , 2002b ). Plant growth regulating herbicides that mimic indole-3-acetic acid, like 2,4-dichlorophenoxyacetic acid and clopyralid, have generally provided poor mugwort control, even at high application rates ( Ahrens, 1976 ; Bingham, 1965
; Weaver, 1984 ). As with most minor crops, registered herbicides for use in cabbage are limited. Bensulide, clomazone, DCPA, oxyfluorfen, and trifluralin are registered for preplant incorporated application ( Zotarelli et al., 2016 ). Clethodim, clopyralid
The IR-4 program works to identify potential minor-use horticultural chemicals and evaluate them for phytotoxicity and efficacy. The objective of this experiment was to evaluate phytotoxicity and weed control of three unlabeled herbicides on field production of Hemerocallis spp. `Ming Toy'. Ten-cm pots of `Ming Toy' were planted into the field 16 July 2001. Each plot consisted of 3 plants per treatment with 6 replications in a completely random design. Each herbicide was analyzed as a separate experiment. Herbicide treatments consisted of clopyralid (0.14, 0.28, 0.56, or 1.1 kg·ha-1 a.i.), clethodim (125, 250, or 500 mL·L-1 a.i.), or bentazon (1.1, 2.2, or 4.4 kg·ha-1 a.i.). Data collected included weed number, percentage of weed coverage (% weed coverage), and phytotoxicity and foliar color ratings for `Ming Toy'. Clopyralid reduced total weed number 90 DAT although % weed coverage was similar or worse compared to the control treatment. Phytotoxicity 90 DAT was not significant for plants treated with clopyralid, but foliar color ratings were reduced. Application of clethodim to `Ming Toy' plots, regardless of rate, resulted in similar weed numbers compared to the control 49 DAT. Clethodim application, regardless of rate, reduced % weed coverage compared to the control treatment. Phytotoxicity 90 DAT was not significant, regardless of herbicide treatment, but foliar color ratings were lower for herbicide treated plants compared to the control. Bentazon, regardless of rate, reduced weed number and % weed coverage 49 DAT compared to the control. Phytotoxicity was similar to the control for plants treated with 1.1 kg·ha-1 a.i.