Absorption and Translocation of Aminocyclopyrachlor and ... - naldc

Weed Science 2010 58:96–102

Absorption and Translocation of Aminocyclopyrachlor and Aminocyclopyrachlor-Methyl Ester in Canada Thistle (Cirsium arvense) Bekir Bukun, R. Bradley Lindenmayer, Scott J. Nissen, Philip Westra, Dale L. Shaner, and Galen Brunk* Laboratory studies were conducted using 14C-aminocyclopyrachlor (DPX-MAT28) and its 14C-methyl ester formulation (DPX-KJM44) to (1) determine the adjuvants’ effects on absorption, (2) compare the absorption and translocation of aminocyclopyrachlor free acid with the methyl ester, and (3) determine the rate at which aminocyclopyrachlor-methyl ester is metabolized to the free acid in Canada thistle. Canada thistle plants were grown from root cuttings and treated in the rosette growth stage. The effect of different adjuvants on absorption was determined by treating individual leaves with formulated herbicide plus 14C-herbicide alone or with methylated seed oil (MSO), crop oil concentrate, or nonionic surfactant with and without urea ammonium nitrate and ammonium sulfate. Plants were harvested 96 h after treatment (HAT). For absorption and translocation experiments, plants were oversprayed with aminocyclopyrachlor or its methyl ester at a rate of 0.14 kg ae ha21 in combination with 1% MSO. Formulated herbicide plus 14C-herbicide was then applied to a protected leaf, and plants were harvested 24 to 192 HAT. Plants were harvested and radioactivity was determined in the treated leaf and in aboveground and belowground tissues. Metabolism of aminocyclopyrachlor-methyl ester to the free acid was determined 2, 6, and 24 HAT. All aboveground biomass was analyzed by high-performance liquid chromatography to establish the ratio of methyl ester to free acid. MSO applied with either herbicide formulation resulted in the highest absorption compared with no surfactant. Significantly greater aminocyclopyrachlor-methyl ester was absorbed, compared with the free acid, which was reflected in the greater aboveground translocation for the methyl ester. Both formulations had similar amounts of translocation to the roots, with 8.6% (SE 6 3.3) for the methyl ester compared with 6.2% (SE 6 2.5) for the free acid. Approximately 80% of the methyl ester was converted to the free acid at 6 HAT. Based on this conversion rate, aminocyclopyrachlor translocated as the free acid in Canada thistle. Nomenclature: Aminocyclopyrachlor (6-amino-5-chloro-2-cyclopropyl-4-pyrimidinecarboxylic acid); aminocyclopyrachlor-methyl ester (6-amino-5-chloro-2-cyclopropyl-4-pyrimidin methyl ester); Canada thistle, Cirsium arvense L. CIRAR. Key words: DPX-MAT28, DPX-KJM44, translocation, absorption, metabolism.

Canada thistle has reproductive strategies that allow it to invade and persist in a variety of habitats (Mesbah and Miller 2005; Slotta et al. 2006), including cropland, pasture, range, and riparian environments. Riparian areas are especially vulnerable because Canada thistle invasion can take advantage of higher soil-moisture levels and proliferate. In addition, riparian corridors are among the most biologically diverse environments in the western United States and represent important wildlife habitat (DiTomaso 1998). Controlling Canada thistle in riparian areas has always been difficult because of registration restrictions for several effective herbicides. These herbicides are not labeled for use near water, or they have groundwater advisories that limit use in riparian environments (Bukun et al. 2009). That situation recently changed with the introduction of a new herbicide, aminopyralid. Aminopyralid provides Canada thistle control equivalent to picloram and clopyralid (Enloe et al. 2007), and it can be used in riparian areas. Aminopyralid’s commercialization represents one of only a handful of instances when a new herbicide was made available for noncrop uses before it was introduced for use in a major commodity. DuPont (Wilmington, DE) is continuing this trend with the introduction of a new active ingredient, aminocyclopyrachlor (Figure 1a). Aminocyclopyrachlor, previously known as DPXMAT28, and the methyl ester formulation, previously known as DPX-KJM44 (Figure 1b), are in development for rangeland, pasture, noncropland, and natural areas to control many weedy DOI: 10.1614/WS-09-086.1 * First author: Department of Plant Protection, Harran University, 63100 Sanliurfa, Turkey; second, third, fourth, and sixth authors: Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO 80523; fifth author: U.S. Department of Agriculture–Agricultural Research Service, Water Management Research Unit, Fort Collins, CO 80526. Corresponding author’s E-mail: [email protected]

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broadleaf species, including Canada thistle. DuPont and university researchers report broad-spectrum activity on several species in the Asteraceae, Fabaceae, Chenopodiaceae, Convolvulaceae, Solanaceae, and Euphorbiaceae families (Armel et al. 2009; Blair and Lowe 2009; Bukun et al. 2008; Claus et al. 2008; Evans et al. 2009; Gannon et al. 2009; Montgomery et al. 2009; Roten et al. 2009; Turner et al. 2009; Westra et al. 2008a,b; Wilson et al. 2009). This herbicide also has the potential to control several acetolactate synthase–, protoporphyrinogen oxidase–, triazine-, and glyphosate-resistant species (Claus et al. 2008; Montgomery et al. 2009; Wilson et al. 2009). Aminocyclopyrachlor is the first pyrimidine carboxylic acid herbicide. It has structural similarities to the pyridine carboxylic acid herbicides, picloram, clopyralid, and aminopyralid (Sensenman 2007). However, aminocyclopyrachlor has one additional nitrogen atom in the heterocyclic ring and a cyclopropyl side chain (Figure 1). Amimocyclopyrachlor’s mode of action has not been disclosed or is unknown. Commonly observed symptoms on a number of broadleaf species are leaf and stem epinasty, which is indicative of an auxinic mode of action (Bukun et al. 2008; Sensenman, 2007; Westra et al. 2009). Aminocyclopyrachlor acid has a dissociation constant (pKa) of 4.65, which is similar to other phloem mobile herbicides (Hsu and Kleier 1996). Research with other weak acid herbicides has indicated that this is an ideal pKa to promote plasma membrane transport and long-distance phloem translocation (Devine et al. 1987; Kleier 1988). Although aminocyclopyrachlor’s log octanol–water partition coefficient (log Kow) increases from 22.48 to 21.12 when the pH of the aqueous solution is lowered from pH 7 to 4 (Finkelstein et al. 2008), the un-ionized form of the molecule remains highly water soluble. The additional nitrogen of the pyrimidine ring

placed in a growth chamber1 for 10 d at 20/10 C day/night temperatures, instead of 24/15 C day/night temperatures. Second, the pots2 with emerged shoots were kept in the same growth chamber for 45 d before herbicide application and were not grown outdoors, as previously described.

Figure 1. Chemical structures of (A) aminocyclopyrachlor and (B) aminocyclopyrachlor-methyl ester.

may impart sufficient polarity to the molecule that neutralizing the charge associated with the carboxylic acid does not result in a molecule that is lipophilic (denoted by a positive log Kow). This could have significant effects on translocation of the aminocyclopyrachlor free acid. Based on the model of phloem mobility proposed by Hsu and Kleier (1996), the log Kow of aminocyclopyrachlor is too low to promote phloem translocation, even with a pKa in the optimal physiological range. Compared with the free acid, aminocyclopyrachlor-methyl ester is lipophilic (log Kow 1.87). Herbicides are commonly formulated as methyl or ethyl ester, even though the active form of the molecule is the free acid (Bravin et al. 2000; Davidonis et al. 1980; Dayan et al. 1997; Devine et al. 1993; Douglas et al. 1985). We hypothesize that the lipophilic nature of the ester will allow for rapid cuticle penetration, and then esterase activity in the cuticle and epidermal cell walls will rapidly release the free acid. This rapid conversion to the free acid would promote a strong concentration gradient across the cuticle, whereas the free acid is physiologically suited to long-distance phloem transport. Carfentrazone-ethyl ester, fluazifop-P butyl ester, and various auxinic herbicide esters are just a few examples of herbicides applied as proherbicides, which require plant esterase activity for bioactivation to produce the herbicidal free acid (Thompson and Nissen 2000). There is little information about the absorption and translocation of these new molecules in any plant species; therefore, the objectives of these laboratory studies were to (1) determine the effects of different adjuvants on absorption, (2) compare absorption and translocation of aminocyclopyrachlor free acid with the methyl ester, and (3) determine the rate at which aminocyclopyrachlor-methyl ester is metabolized to the free acid in Canada thistle. Understanding the behavior of these new molecules will provide valuable information about the advantages and disadvantages of each formulation and may help to explain differences in biological activity observed in the field (P. Westra, personal communication). Canada thistle was selected as the test species to make relative comparisons with previously published research evaluating clopyralid and aminopyralid absorption and translocation in the same species (Bukun et al. 2009). Materials and Methods

Plant Materials. Root collection and transplanting methods were consistent with Bukun et al. (2009) with two exceptions. First, root segments were wrapped in moist paper towels and

Adjuvants. The effect of adjuvants on aminocyclopyrachlormethyl ester and aminocyclopyrachlor absorption were evaluated using methylated seed oil3 (MSO), crop oil concentrate4 (COC), nonionic surfactant5 (NIS), NIS plus ammonium sulfate (AMS), and NIS plus urea ammonium nitrate (UAN). Solutions were 1% MS0 (v/v), 1% COC (v/v), 0.25% NIS (v/v), 0.25% NIS plus 1.2% AMS (wt/v), and 0.25% NIS plus 1% UAN (v/v) combined with formulated product at a rate of 0.14 kg ae ha21 of aminocyclopyrachlormethyl ester6 or aminocyclopyrachlor.7 Treatment solutions were prepared by adding 5 kBq of aminocyclopyrachlor-methyl ester (2-14C pyrimidyl, specific activity of 3.722 3 108 kBq mmol21) or 5 kBq of aminocyclopyrachlor (pyrimidine 2-14C, specific activity of 3.50 3 108 kBq mmol21) to 0.5 ml of the each adjuvant combination. These treatment solutions were used to treat individual leaves with 20, 0.5-ml drops (96 Bq plant21) of application solution. Plants were in the rosette growth stage at the time of treatment. Plants were grown with a 12 h photoperiod (approximately 200 mE m22 s21). Treated leaves were harvested 96 HAT and placed in 20-ml scintillation vials. Treated leaves were shaken for 20 min in 5 ml of a solution containing 90% water, 10% methanol, and 0.25% NIS. Treated leaves were removed from the vial, 10 ml of scintillation cocktail8 were added, and the radioactivity was determined by liquid scintillation spectroscopy9 (LSS). The percentage of aminocyclopyrachlor-methyl ester or aminocyclopyrachlor absorbed was determined as the difference between total radioactivity applied and radioactivity remaining in the leaf wash, divided by the total applied radioactivity. The experiment was a randomized completeblock design with four replicates for each application solution and was repeated. Absorption, Translocation, and Root Exudation. Plants in the five- to six-leaf, rosette stage were treated according to methods previously described (Bukun et al. 2009). The youngest, fully expanded leaf on each plant was covered with aluminum foil to protect it from the overhead application. Formulated aminocyclopyrachlor and aminocyclopyrachlormethyl ester were applied at 0.14 kg ae ha21 with 1% v/v MSO using a single-nozzle, overhead track sprayer,10 calibrated to deliver 187 L ha21 at 206 kPa. Following foliar herbicide applications, the protected leaves were treated with 20, 0.5-ml droplets of a solution containing formulated herbicide, as previously described, plus radiolabeled herbicide. Each plant was treated with 4.2 kBq of radiolabeled aminocyclopyrachlor-methyl ester or the free acid and 1% v/v MSO. Plants were grown as described above following the treatments. Plants were harvested 24, 48, 96, and 192 h after treatment (HAT). At harvest, plants were separated into treated leaf and aboveground and belowground tissue. Plant parts were ovendried at 60 C for 48 h and combusted in a biological oxidizer.11 Radioactivity was trapped with 10 ml of 14C trapping cocktail.12 Sand used as rooting medium was processed and sampled as previously described (Bukun et al.

Bukun et al.: Aminocyclopyrachlor absorption and translocation

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2009). Radioactivity in all plant parts and root exudates was measured using LSS. This experiment was a randomized complete-block design with three replications and was repeated. Herbicide absorption was calculated as the total amount of 14C applied, minus the radioactivity recovered in the leaf wash. Herbicide translocation from the treated leaf was calculated by measuring the total radioactivity recovered in all plant parts other than the treated leaf, then dividing that by the total radioactivity applied. It should be noted that the above and below, treated, leaf shoot material were combined and referred to as aboveground plant parts. Radioactivity exuded from the roots was also included in total translocation to the root. Metabolism. To determine the conversion rate of aminocyclopyrachlor-methyl ester to aminocyclopyrachlor, radiolabeled aminocyclopyrachlor-methyl ester was applied to Canada thistle plants as previously described. All aboveground plant material was harvested at 0, 2, 6, and 24 HAT and was prepared as reported in Bukun et al. (2009). Highperformance liquid chromatography13 (HPLC) was used to determine whether the radioactivity in each sample was the intact methyl ester or the free acid of aminocyclopyrachlor. HPLC parameters were the same as those previously described (Bukun et al. 2009). This experiment was a randomized complete-block design with three replications and was repeated. Data Analysis. Data from all experiments were subjected to Levene’s test for homogeneity of variance to determine whether the data from repeat experiments could be pooled (SAS 2004). ANOVA was then performed on data sets for each experiment, and treatment means for the surfactant experiment were compared using Fisher’s Protected LSD test (P # 0.05). Data for all time-course experiments were analyzed using nonlinear regression in SigmaPlot14 version 9. Results and Discussion

Adjuvants. Levene’s test for homogeneity of variance indicated that experiments could be combined (P , 0.05). When applied without adjuvant, aminocyclopyrachlor-methyl ester had significantly greater absorption than the free acid (Figure 2). This result was not unexpected because the two molecules have very different log Kow values, with aminocyclopyrachlor-methyl ester being more lipophilic than the free acid. Aminocyclopyrachlor-methyl ester and the free acid had significantly greater absorption when combined with certain adjuvants, especially MSO and COC. Oil-based adjuvants are thought to increase herbicide diffusion by increasing the fluidity of cuticular components (Santier and Chamel 1998). Nalewaja and Skypczak (1986) also found a correlation between wax solubilization and herbicide penetration with MSO. The addition of NIS to the treatment solution significantly increased absorption of aminocyclopyrachlor-methyl ester and the free acid, however, not to the same extent as the COC or the MSO. Cuticular hydration by NIS may enhance foliar absorption of water-soluble herbicides (Coret and Chamel 1993); however, when aminocyclopyrachlor was combined with NIS alone, there was significantly less absorption than with either MSO or COC (Figure 2). These results could be 98

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Figure 2. Foliar absorption of 14C-aminocyclopyrachlor-methyl ester (AMCPME) and aminocyclopyrachlor (AMCP) with different surfactant and adjuvant combinations. These data are based on the amount of radioactivity recovered in the leaf wash. Surfactants were methylated seed oil (MSO), crop oil concentrate (COC), nonionic surfactant (NIS) alone and applied in combination with ammonium sulfate (AMS), and NIS in combination with urea ammonium nitrate (UAN). Letters are the result of Fisher’s Protected LSD test (P , 0.05).

confounded by both MSO and COC containing about 15% NIS, which means that the free acid could benefit from the combined interaction of the oil and the NIS because a 1% solution of MSO or COC contains a similar amount of NIS as a 0.25% solution of NIS alone. Aminocyclopyrachlor-methyl ester absorption when combined with NIS plus AMS or with NIS plus UAN was not statistically different than the water control, whereas the combination of the free acid formulation and NIS plus AMS provided significantly better absorption than NIS alone (Figure 2). In a study comparing aminopyralid behavior in Canada thistle, absorption was consistent with the idea that NIS would be the most appropriate surfactant for a water-soluble herbicide (Bukun et al. 2009). NIS, NIS plus AMS, and NIS plus UAN provided the greatest absorption, whereas absorption with MSO and COC were not significantly different from the water-only control. Unlike aminopyralid, the absorption of the water-soluble free acid, aminocyclopyrachlor, was enhanced by MSO and COC more than with NIS. This current research clearly indicates that MSO was the most appropriate adjuvant for use with both aminocyclopyrachlor-methyl ester and the water-soluble free acid. Because most field evaluations have included MSO as the adjuvant, improving field-level biological activity by manipulating the spray solutions with other adjuvant combinations seems unlikely. Absorption, Translocation, and Root Exudation. Levene’s test for homogeneity of variance indicated that experiments could be pooled for analysis (P , 0.05). In these experiments, 78% (6 2.2%) and 80% (6 2.2%) of the total 14Caminocylcopyrachlor-methyl ester and free acid were recovered, respectively (data not shown). This recovery is less than what has been reported in previous research (Bukun et al. 2009), but it is within acceptable levels considering losses during plant harvest, and drying and recovery efficiencies during sample oxidation.

Figure 3. Foliar absorption of 14C-Aminocyclopyrachlor-methyl ester (AMCPME) and aminocyclopyrachlor (AMCP) during a 192-h time course. These data are based on the amount of radioactivity recovered in the leaf wash. Formulated herbicide plus radiolabeled herbicide was combined with 1% methylated seed oil (MSO). Data points are means and standard errors. AMCP-ME regression (P , 0.0001): y 5 83.7(1 2 e20.3x ). AMCP regression (P , 0.0001): y 5 56.6(1 2 e20.3x ).

Both herbicides achieved maximum absorption 24 HAT, and absorption remained unchanged up to 192 HAT (Figure 3). Aminocyclopyrachlor-methyl ester absorption was 27% greater than the free acid absorption 24 HAT at 84% (6 9.4) compared with 57% (6 14.6), respectively. This difference in absorption is explained by comparing the log Kow values for aminocyclopyrachlor-methyl ester and the free acid. As previously mentioned, aminocyclopyrachlormethyl ester has greater lipophilicity than the free acid does, resulting in significantly greater cuticle penetration. Although not comparable statistically, previous research with clopyralid and aminopyralid absorption in Canada thistle has shown several similarities with the current study (Bukun et al. 2009). Aminocyclopyrachlor-methyl ester and clopyralid show similar rates and maximum absorption levels (84% compared with 78%, respectively), whereas aminocyclopyrachlor and aminopyralid have different absorption rates, reaching nearly identical maximum absorption levels (approximately 57%). Aminocyclopyrachlor-methyl ester aboveground translocation from the treated leaf was significantly greater than the free acid (Figure 4a) when calculated as a percentage of applied radioactivity. The greater translocation of aminocyclopyrachlor-methyl ester was due to the more efficient absorption of the ester formulation, which created a stronger concentration gradient, which resulted in greater movement out of the treated leaf. Aminocyclopyrachlor-methyl ester had significantly greater foliar absorption, translocation from the treated leaf, and accumulation in aboveground plant parts than the free acid; however, both forms of the herbicide had similar translocation patterns to Canada thistle roots (Figure 4b). The amount of herbicide accumulating in Canada thistle roots was 8.6% (SE 6 3.3) and 6.2% (SE 6 3.5) when the herbicide as applied as the methyl ester and free acid, respectively. Aminocyclopyrachlor-methyl ester translocation reached a maximum at 96 HAT, whereas translocation of the free acid reached a maximum much later at 192 HAT (Figure 4b). Aminocyclo-

Figure 4. (A) Total translocation of 14C-aminocyclopyrachlor-methyl ester (AMCP-ME) and aminocyclopyrachlor (AMCP) in the plant as a percentage of the applied herbicide during the 192-h period. Data points are means and standard errors. AMCP-ME regression (P , 0.0001): y 5 37.5(1 2 e20.04x ) AMCP regression (P , 0.0001): y 5 26.1(1 2 e20.03x ). (B) Translocation to aboveground and belowground tissues of AMCP-ME and AMCP as a percentage of the applied herbicide during the 192-h period including the treated leaf. Data points are means and standard errors. AMCP-ME aboveground regression (P , 0.0001): y 5 29.7(1 2 e20.03x ), belowground regression (P , 0.0001): y 5 8.6(1 2 e20.06x ). AMCP aboveground regression (P , 0.0001): y 5 20.2(1 2 e 20.02x ), belowground regression (P , 0.0001): y 5 6.2(1 2 e 20.9x ).

pyrachlor-methyl and the free acid translocation were modeled best with a nonlinear equation. The amount of radiolabeled herbicide translocating to Canada thistle roots was similar to chlorsulfuron (5%) translocation, but much less than the amount of clopyralid (29%) recovered from Canada thistle roots 144 HAT (Devine and Vanden Born, 1985). In a previous study, comparing clopyralid and aminopyralid translocation in Canada thistle, clopyralid and aminopyralid translocation were similar to aminocyclopyrachlor-methyl ester and its free acid, respectively (Bukun et al. 2009). The relatively low translocation to belowground tissue could be attributed to poor phloem mobility or to the young growth stage of the plants used in this study. Interestingly, the amount of radioactivity remaining in the treated leaf 192 HAT was different for the two formulations. When aminocyclopyrachlor-methyl ester was applied, 11.1% (SE 6 5.1) of applied radioactivity remained in the treated leaf, compared with 2.8% (SE 6 0.5) when radioactivity was applied as the free acid. Several previous studies have demonstrated that not all the herbicide translocation to the root system of herbaceous


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Figure 5. Conversion of aminocyclopyrachlor-methyl ester (AMCP-ME) to aminocyclopyrachlor (AMCP) during a 24-h period. Data points are means and x{1 standard errors. AMCP-ME (P , 0.0001): y~82:6|e{eð{ 0:63 Þ . AMCP regression (P , 0.0001): y 5 29.4x(20.26).

perennial weeds is retained. In leafy spurge for example, a significant percentage of the radioactivity from picloram and imazapyr applications that translocated to the root system was in the rooting media (Lym and Moxness 1989; Nissen et al. 1995). For aminocyclopyrachlor and its methyl ester, the amount of applied radioactivity recovered from the rooting media was 4.5% (SE 6 1.2) and 3.6% (SE 6 1.2), respectively. Similar amounts of root exudation were previously reported for clopyralid and aminopyralid in Canada thistle (Bukun et al. 2009). Metabolism. HPLC analyses of plant extracts indicated that aminocyclopyrachlor-methyl ester was rapidly metabolized to the free acid. By 2 HAT, 65% (SE 6 6.0%) of the radioactivity found in the plant extracts was aminocyclopyrachlor and at 6 HAT, 82% (SE 6 10.1) of the methyl ester had been metabolized to the free acid (Figure 5). Herbicides are frequently formulated as inactive, proherbicidal, carboxylic esters to facilitate their passage through the waxy cuticles of plant leaves (Gershater and Edwards 2007). Once the ester has passed through the cuticle, carboxylesterases metabolize the ester to form the phytotoxic free acid. The best-known examples of this hydrolytic bioactivation are the esters of 2,4-dichlorophenoxyacetic acid (2,4-D) and the aryloxyphenoxypropionates (Gershater and Edwards 2007); however, this conversion is not limited to auxin or acetyl-CoA carboxylase herbicides. The protoporphyrinogen oxidase inhibitor, carfentrazone ethyl ester, was reported to be almost totally metabolized to the phytotoxic free acid 2 HAT in velvetleaf (Abutilon theophrasti Medik.) (Thompson and Nissen 2000). Recent studies have also shown that specific enzymes, such as AmGDSH1, localized in the apoplast, hydrolyzed 2,4-D methyl ester to release the phytotoxic acid 2,4-D (Gershater et al. 2007). The main advantage of aminocyclopyrachlor-methyl ester appears to be more-rapid initial absorption when compared with the free acid. When the amount of radiolabeled herbicide translocated from the treated leaf was calculated as a percentage of the absorbed radioactivity, there was no difference between aminocyclopyrachlor-methyl ester and the free acid (Figure 6). This observation, combined with 100

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Figure 6. Aminocyclopyrachlor-methyl ester (AMCP-ME) and aminocyclopyrachlor (AMCP) translocation out of the treated leaf as a percentage of the absorbed herbicide during the 192-h period. Data points are means and standard errors. AMCP-ME regression (P , 0.0001): y 5 45.5(1 2 e20.04x ). AMCP regression (P , 0.0001): y 5 46.6(1 2 e20.03x ).

the rapid metabolism of the methyl ester to the free acid, suggests that it is the free acid that is phloem mobile. The percentage of applied radioactivity translocating to Canada thistle roots was the same with both formulations, providing additional evidence that the herbicide translocates as the free acid. In summary, MSO maximized absorption of both formulations, even for the water-soluble free acid. Because MSO has been the recommended adjuvant for field evaluations, data collected from these experiments should provide an accurate assessment of the herbicide’s biological activity. Aminocyclopyrachlor-methyl ester was absorbed more by the leaves than the free acid, which resulted in greater aboveground translocation but not in greater translocation to Canada thistle roots. This is consistent with field observations where aminocyclopyrachlor-methyl ester has provided more-rapid foliar injury than the free acid; however, Canada thistle control 1 yr after treatment appears to be equivalent with both formulations (P. Westra, personal communication). Most of the applied aminocyclopyrachlormethyl ester was metabolized to the free acid at 6 HAT, which is similar to other herbicides applied as pro-herbicidal methyl and ethyl esters (Gershater and Edwards 2007; Gershater et al. 2007; Thompson and Nissen 2000). Bukun et al. (2009) demonstrated that the auxin herbicide aminopyralid had less translocation to Canada thistle roots than clopyralid, although aminopyralid provides greater Canada thistle control at lower use rates (Enloe 2007). These researchers speculated that aminopyralid may have greater biological activity compared with clopyralid. Our current research indicates that aminopyralid and aminocyclopyrachlor have similar patterns of absorption and translocation. Although aminocyclopyrachlor’s absorption appears to be more rapid than aminopyralid, both herbicides reach a maximum absorption of approximately 60% during a 192-h time course. The amount of herbicide translocated to Canada thistle roots was also similar for aminopyralid and aminocyclopyrachlor (Bukun et al. 2009). Based on this information, it seems reasonable to suggest that aminocyclopyrachlor, like aminopyralid, may have greater biological activity than many

other auxin herbicides, perhaps because of more-favorable binding kinetics at the site of action (Bukun et al. 2009). The one parameter that has yet to be determined for these new auxin herbicides is the importance of soil residual activity for long-term weed management.

Sources of Materials 1

Conviron Controlled Environments Ltd. (model 15), Winnipeg, MB Canada. 2 Deepot cones, Stuewe and Sons, Inc., Corvallis, OR 97333. 3 MSO concentrate with LECI-Tech, Loveland Industries, Inc., Greeley, CO 80537. 4 Maximizer crop oil concentrate, Loveland Industries, Inc., Greeley, CO 80537. 5 Activator 90 nonionic surfactant, Loveland Industries, Inc., Greeley, CO 80537. 6 Aminocyclopyrachlor-methyl ester, DuPont, Wilmington, DE 19898. 7 Aminocyclopyrachlor, DuPont, Wilmington, DE 19898. 8 Ultima Gold LLT (6013371), Perkin Elmer Life and Analytical Sciences, Inc., Waltham, MA 02451. 9 Packard Tri-Carb (model 2500 TR), Packard Instrument Co., Meriden, CT 06450. 10 DeVries Manufacturing Corp., Hollandale, MN 56045. 11 OX-500, R. J. Harvey Instrument Co., Tappan, NY 10983. 12 OX-161, R. J. Harvey Instrument Co., Tappan, NY 10983. 13 Hitachi Instruments, Inc., San Jose, CA 95134. 14 Systat Software, Inc., San Jose, CA 95110.

Acknowledgments The authors would like to thank DuPont Crop Protection for partial financial support and the Scientific and Technological Research Council of Turkey (TUBITAK) for partial postdoctoral support of the first author.

Literature Cited Armel, G. R., W. E. Klingeman, P. C. Flanagan, G. K. Breeden, and M. Halcomb. 2009. Comparisons of the experimental herbicide DPX-KJM44 with aminopyralid for control of key invasive weeds in Tennessee. Abstract 410 in Proceedings of the 49th annual WSSA meeting in Orlando, FL. Champaign, IL: Weed Science Society of America. Blair, M. and Z. Lowe. 2009. Evaluation of KJM-44 for marestail (Conyza canadensis) and total vegetation control. Abstract 406 in Proceedings of the 49th annual WSSA meeting in Orlando, FL. Champaign, IL: Weed Science Society of America. Bravin, F., G. Zanin, and C. Preston. 2000. Resistance to diclofop-methyl in two Lolium spp. populations from Italy: studies on the mechanism of resistance. Weed Res. 41(5):461–473. Bukun, B., T. A. Gaines, S. J. Nissen, P. Westra, G. Brunk, D. L. Shaner, B. B. Sleugh, and V. F. Peterson. 2009. Aminopyralid and clopyralid absorption and translocation in Canada thistle (Cirsium arvense). Weed Sci. 57:10–15. Bukun, B., S. J. Nissen, P. Westra, G. Brunk, D. Shaner, and T. Gaines. 2008. Absorption and translocation of 14C DPX-KJM44 and DPX-MAT28 in Cirsium arvense (Canada thistle). Page 277 in Proceedings of the 5th International Weed Science Congress. Vancouver, BC: International Weed Science Society. Claus, J., R. Turner, G. Armel, and M. Holliday. 2008. DuPont Aminocyclopyrachlor (proposed common name)(DPX-MAT28/KJM44) herbicide for use in turf, IWC, bare-ground and brush markets. Page 277 in Proceedings of the 5th International Weed Science Congress. Vancouver, BC: International Weed Science Society. Coret, J. M. and A. R. Chamel. 1993. Influence of some nonionic surfactants on water sorption by isolated tomato fruit cuticles in relation to cuticular penetration of glyphosate. Pestic. Sci. 38:27–32.

Davidonis, G. H., R. H. Hamilton, and R. O. Mumma. 1980. Metabolism of 2,4-dichlorophenoxyacetic acid (2,4-D) in soybean root callus: evidence for the conversion of 2,4-D amino acid conjugates to free 2,4-D. Plant Physiol. 66:537–540. Dayan, F. E., S. O. Duke, J. D. Weete, and H. G. Hancock. 1997. Selectivity and mode of action of carfentrazone-ethyl, a novel phenyl triazolinone herbicide. Pestic. Sci. 51:65–73. Devine, M. D., H. D. Bestman, and W. H. Vanden Born. 1987. Uptake and accumulation of the herbicides chlorsulfuron and clopyralid in excised pea root tissue. Plant Physiol. 85:82–86. Devine, M., O. S. Duke, and C. Fedtke. 1993. Physiology of Herbicide Action. Englewood Cliffs, NJ: P.T.R Prentice–Hall. Devine, M. D. and W. H. Vanden Born. 1985. Absorption, translocation, and foliar activity of clopyralid and chlorsulfuron in Canada thistle (Cirsium arvense) and perennial sowthistle (Sonchus arvensis). Weed Sci. 33:524–530. DiTomaso, J. M. 1998. Impact, biology, and ecology of saltcedar (Tamarix spp.) in the southwestern United States. Weed Technol. 12:326–336. Douglas, D. B., B. A. Swisher, and O. C. Burnside. 1985. Behavior of 14Chaloxyfop-methyl in intact plants and cell cultures. Weed Sci. 33:291–299. Enloe, S. F., R. G. Lym, and R. Wilson, et al. 2007. Canada thistle (Cirsium arvense) control with aminopyralid in range, pasture, and noncrop areas. Weed Technol. 21:890–894. Evans, C. C., D. P. Montgomery, and D. L. Martin. 2009. Musk thistle control on Oklahoma highway rights-of-way with DPX-KJM44. Abstract 420 in Proceedings of the 49th annual WSSA meeting in Orlando, FL. Champaign, IL: Weed Science Society of America. Finkelstein, B. L., G. R. Armel, and S. A. Bolgunas, et al. 2008. Discovery of aminocyclopyrachlor (proposed common name) (DPX-MAT28): a new broad-spectrum auxinic herbicide. Abstract 19 in Proceedings of the 236th ACS National Meeting in Philadelphia, PA. Washington, DC: American Chemical Society. Gannon, T. W., F. H. Yelverton, L. S. Warren, and C. A. Silcox. 2009. Broadleaf weed control with aminocyclopyrachlor (DPX-KJM44) in fine turf. Abstract 394 in Proceedings of the 49th annual WSSA meeting in Orlando, FL. Champaign, IL: Weed Science Society of America. Gershater, M. C. and R. Edwards. 2007. Regulating biological activity in plants with carboxylesterases. Plant Sci. 173(6):579–588. Gershater, M. C., I. Cummins, and R. Edwards. 2007. Role of a carboxylesterase in herbicide bioactivation in Arabidopsis thaliana. J. Biol. Chem. 282(29):21,460–21,466. Hsu, F. C. and D. A. Kleier. 1996. Phloem mobility of xenobiotics, VIII: a short review. J. Exp. Bot. 47:1265–1271. Kleier, D. A. 1988. Phloem mobility of xenobiotics, 1: mathematical model unifying the weak acid and intermediate permeability theories. Plant Physiol. 86:803–810. Lym, R. G. and Y. D. Moxness. 1989. Absorption, translocation, and metabolism of picloram and 2,4-D in leafy spurge (Euphorbia esula). Weed Sci. 37:498–502. Mesbah, A. O. and S. D. Miller. 2005. Canada thistle (Cirsium arvense) control in established alfalfa (Medicago sativa) grown for seed production. Weed Technol. 19:1025–1029. Montgomery, D., C. Evans, and D. Martin. 2009. Control of kochia with DPXKJM44 along Oklahoma highway rights-of-way. Abstract 493 in Proceedings of the 49th annual WSSA meeting in Orlando, FL. Champaign, IL: Weed Science Society of America. Nalewaja, J. D. and G. A. Skrzypczak. 1986. Absorption and translocation of fluazifop with additives. Weed Sci. 34:572–576. Nissen, S. J., R. A. Masters, W. M. Thompson, and R. N. Stougaard. 1995. Absorption and fate of imazapyr in leafy spurge (Euphorbia esula). Pestic. Sci. 45:325–329. Roten, R. L., R. J. Richardson, and A. P. Gardner. 2009. Responses of selected woody plants to DPX-KJM44. Abstract 418 in Proceedings of the 49th annual WSSA meeting in Orlando, FL. Champaign, IL: Weed Science Society of America. Santier, S. and C. Chamel. 1998. Reassessment of the role of cuticular waxes in the transfer of organic molecules through plant cuticles. Plant Physiol. Biochem. 36(3):225–231. Sensenman, S. A. 2007. Herbicide Handbook 9th Edition. Lawrence, KS: Weed Science Society of America. SAS Institute Inc. 2004. SAS OnlineDoc 9.1.3. Cary, NC: SAS Institute. Slotta, T.A.B., J. Rothhouse, D. P. Horvath, and M. E. Foley. 2006. Genetic diversity of Canada thistle (Cirsium arvense) in North Dakota. Weed Sci. 54:1080–1085. Thompson, W. M. and S. J. Nissen. 2000. Absorption and fate of carfentrazoneethyl in Zea mays, Glycine max, and Abutilon theophrasti. Weed Sci. 48:15–19. Turner, R. G., J. S. Claus, E. Hidalgo, M. J. Holliday, and G. R. Armel. 2009. Technical Introduction of the new DuPont vegetation management herbicide


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aminocyclopyrachlor. Abstract 405 in Proceedings of the 49th annual WSSA meeting in Orlando, FL. Champaign, IL: Weed Science Society of America. Westra, P., S. Nissen, D. Shaner, and T. Gaines. 2008a. Invasive weed management and plantback crop response with the new herbicide KJM-44. Page 303 in Proceedings of the 5th International Weed Science Congress in Vancouver, BC, Canada. International Weed Science Society. Westra, P., S. Nissen, D. Shaner, B. Lindenmayer, and G. Brunk. 2009. Invasive weed Management with Aminocyclopyrachlor in the central great plains. Abstract 407 in Proceedings of the 49th annual WSSA meeting in Orlando, FL. Champaign, IL: Weed Science Society of America.

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Westra, P., R. Wilson, and M. Edwards. 2008b. Agronomic crop response to KJM-44 herbicide. Abstract 155 in Proceedings of the 60th WSWS annual meeting in Anaheim, CA. Las Cruces, NM: Western Society of Weed Science. Wilson, M. J., J. K. Norsworthy, S. Bangarwa, G. Griffith, J. Still, and R. Scott. 2009. Effect of rate and timing on broadleaf weed control in rice with DPXKJM44. Abstract 332 in Proceedings of the 49th annual WSSA meeting in Orlando, FL. Champaign, IL: Weed Science Society of America.

Received May 15, 2009, and approved December 3, 2009.