Metolachlor and metribuzin loss in runoff was determined in three soybean tillage systems with and without a 4 by 2 m tall fescue vegetative filter strip. Soil erosion plots were 4 by 22 m with 3% slope. Regression analysis was used to describe herbicide concentration in runoff, and to determine if vegetative filter strips reduced herbicide concentration. Analysis of covariance indicated no difference in concentration of metolachlor or metribuzin in runoff from the three tillage systems within any vegetative filter strip treatment. Metolachlor loss in 1991 was highest from the no-till monocrop without a vegetative filter strip, and it was 65g ha−1 or approximately 2% of the amount applied. In 1992 and 1993, the no-till doublecrop had a total loss of 120 and 147 g ha−1, respectively, approximately 4% of the amount applied. Similar results were noted with metribuzin, but total loss was as high as 46 g ha−1 or 11 % of the amount applied in 1993 from a no-till doublecrop system without a vegetative filter strip. When a vegetative filter strip was present, losses of metribuzin and metolachlor were reduced over 85% in 1993, and totaled 1.2 and 0.5%, respectively, of the amount applied. The vegetative filter strip reduced herbicide and suspended solids from runoff produced by a conventional-till production system to levels equal to or lower than a no-till doublecrop system.

Tall fescue vegetative filter strips 0.5 to 4.0 m wide were evaluated for their ability to reduce losses of metolachlor, metribuzin, and runoff (water and sediment) in conventionally tilled soybean. Differences in the parameters studied were significant between filter and no filter strips, regardless of filter strip width. Two days after treatment, metribuzin concentration in runoff from the unfiltered treatment was 231 ng ml−1; filter strips reduced this amount to 119 ng ml−1 or less. Similar trends were observed with metolachlor, with concentrations of 1,009 ng ml−1 from the unfiltered, whereas filter strips of any width reduced this to 523 ng ml−1 or less. Metribuzin loss during the growing season was 41 g ai ha−1, or 9.8% of the amount applied when no filter strip was present. The addition of a filter strip, regardless of width, reduced cumulative metribuzin losses to 11 g ha−1 or less. Similar results were noted with metolachlor. Filter strips, regardless of width, reduced cumulative runoff and sediment loss at least 46 and 83%, respectively.

Absorption and translocation of 14C-ethalfluralin (N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine) were measured in cucumber plants in the field and greenhouse. In field enclosures, cucumbers treated with 1.68 or 3.36 kg ai/ha preemergence soil-surface applications of 14C-ethalfluralin accumulated significantly more 14C in leaves than in petioles, stems, or fruits. In greenhouse studies, 14C-ethalfluralin vapor was absorbed by both cucumber seedling stems and cotyledons. Seedlings absorbed 14C-ethalfluralin from a nutrient solution and translocated 14C into all plant parts. Cucumber absorbed 14C-ethalfluralin topically applied to the stem and translocated 14C acropetally, while only limited basipetal translocation occurred. Although cotyledons absorbed 14C-ethalfluralin, very little 14 C moved out of the treated tissue.

Surface microrelief and agrichemical placement influence agrichemical movement through soil. This study determined if anhydrous ammonia shank placement influenced atrazine movement in a ridge tillage system. Atrazine and Br− were broadcast over the plot or banded on the ridge while N fertilizer was Injected into the ridge or valley. Rainfall (17 cm) was applied and leachate was collected incrementally from grid lysimeters placed 75 cm below the soil surface. Amounts of atrazine and Br− in leachate and postrainfall soil atrazine distribution were determined. The injection slot created by fertilizer application influenced chemical movement. When atrazine and the fertilizer injection slot overlapped, atrazine movement through the soil was enhanced. These data suggest that herbicide applications and fertilizer injection slots that are not covered should not overlap due to increased potential for movement.

Two lettuce cultivars exhibiting differential levels of tolerance to thiobencarb in soil and nutrient solution assays were examined. Seedlings of ‘Dark Green Boston’ (BOS), a susceptible cultivar, were found to show significant inhibitions in foliar growth compared to the tolerant ‘Great Lakes 366’ (GLA). Reductions of 57% occurred in BOS leaf dry weights at rates of 3 μM thiobencarb as soon as 4 days after treatment. In addition, growth abnormalities including fused leaves were observed in the BOS cultivar, indicating inhibition early in leaf development at the meristem. Twenty-nine and 22% of applied 14C-thiobencarb was absorbed from nutrient solution by BOS and GLA, respectively. This difference is probably due to BOS having a 50% greater root system at the time of treatment. Greater absorption and accumulation of radioactivity in the leaves, as well as significantly greater amounts of parent 14C-thiobencarb in the foliage of BOS compared to GLA (30 and 19%, respectively) may account for the selectivity observed. Metabolism of 14C-thiobencarb occurred within 1 day in both cultivars, with the apparent production of herbicide conjugates accounting for more than 90% of the extracted radiolabel 12 days after treatment. A thiobencarb sulfoxide metabolite was not identified in these studies, indicating sulfoxide production is not a mechanism of selectivity in lettuce.

Preplant-incorporated (PPI) applications of 280 g ai/ha of imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} had significantly greater persistence than preemergence surface (PES) applications throughout the growing season in 1985. In 1984 there was no statistical difference in imazaquin remaining between PPI and PES treatments. Very little imazaquin was detected below 10 cm in the soil profile for all sampling dates each year. Imazaquin dissipated rapidly both years during the first 30 days following PPI and PES applications. A subsequent decrease in the dissipation rate occurred in the next 120 days of the growing season. Spring tillage had no significant effect on injury to corn (Zea mays L.) planted into the field the year following imazaquin application. Corn planted in 1986 into imazaquin-treated plots of 1985 had no growth reduction when compared to corn grown in plots where zero imazaquin had been applied. However, corn planted in 1985 into imazaquin applications of 1984 had significant injury. Greatest injury occurred where imazaquin had been incorporated, and injury increased as imazaquin rate was increased.

Field observations indicate that wheat (Triticum aestivum L.) is considerably more tolerant to soil residues of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} than barley (Hordeum vulgare L.). The basis for relative differences in tolerance was investigated by measuring herbicide dose response, uptake, movement, and metabolism using ‘Clark’ barley and ‘Marberg’ wheat. Barley root fresh and dry weights were significantly reduced when roots were exposed to nutrient solution containing 35 mM chlorsulfuron for 1 day. Wheat roots similarly exposed for 3 days to 1.1 mM chlorsulfuron displayed no growth reduction. The small differences in uptake and movement of chlorsulfuron detected in wheat and barley are inadequate to explain the large response difference between the two species. Both species rapidly metabolize chlorsulfuron in 1 day and there is no significant difference in the level of parent compound remaining in barley compared to wheat. A factor other than uptake, movement, or metabolism must account for barley roots greater sensitivity to root-applied chlorsulfuron.

Three soybean production systems coupled with conventional tillage (CT) or no-tillage (NT) were evaluated for metolachlor and metribuzin loss in water from runoff. Metolachlor and metribuzin concentrations were similar in runoff from CT or NT soybean following winter wheat, with stubble burned, and CT or NT monocrop soybean. However, metolachlor and metribuzin concentrations were higher in runoff water from the CT doublecrop soybean planted into winter wheat stubble than NT. In all 3 yr of the study, the majority of total losses occurred in the first three runoff events. Total loss of metolachlor in runoff from the doublecrop system with winter wheat stubble present was 0.6% in 1991 to 1.1% in 1990 from CT, and 0.2% in 1990 to 0.6% in 1991 from the NT. Similar results were observed from the CT and NT doublecrop with burned winter wheat stubble and the monocrop systems. Metribuzin loss patterns were similar to metolachlor, but the fraction lost was slightly higher. Multi-variate regression was used to describe and predict herbicide losses, and R2values ranged from 0.66 to 0.98 for both metolachlor and metribuzin.

Pesticide leaching experiments using widely spaced sampling sites may not adequately characterize chemical leaching behavior such as nonuniform flow between sampling points. We conducted this study to determine the three-dimensional variability of atrazine and chloride movement within a small volume of soil (2,700 cm1) under field conditions. A 1-m2area of Williamson silt loam (coarse-silty, mixed, mesic, Typic Fragiochrept) was sprayed uniformly with atrazine (1.1 kg ai/ha) and chloride (80 kg/ha). We used the Leaching Estimation and Chemistry Model (LEACHM) to simulate chemical movement. After 6.5 cm of rainfall during a 29-d period, we sampled 36 squares (5 by 5 cm) in the central 30- by 30-cm portion of the treated area at six depth increments (0 to 2, 2 to 5, 5 to 10, 10 to 15, 15 to 21, and 21 to 30 cm) and determined atrazine and Cl−concentrations. We recovered 26% of the applied atrazine and 138% of the applied chloride. Low atrazine recovery may have been due to leaching beyond 30 cm and/or degradation while excess chloride recovery is attributed to high background concentrations. Coefficients of variation (CVs) for atrazine significantly increased with depth and ranged from 26 to 353%, while CVs for Cl−were independent of depth and ranged from 32 to 66%. Derived atrazine concentration isograms illustrated highly nonuniform herbicide transport. Although LEACHM overestimated atrazine movement in the upper 15 cm, it was fairly accurate in the lower 15 cm. The overall trend in Cl−flow was adequately predicted, even though the predicted Cl−concentrations were underestimated. LEACHM could not accurately predict nonuniform flow or the variability in solute concentrations between points. However, its prediction of the atrazine center of mass (about 4.7 cm) agreed well with the derived isograms. These findings demonstrate that localized nonideal solute transport may be missed in larger sampling schemes and in simulation models.

Concern has been raised that herbicides often used to control perennial ryegrass in warm-season turf could move laterally or “track” and injure neighboring cool-season grasses. Rimsulfuron was applied at 17.5 or 35 g ai/ha to perennial ryegrass in the afternoon. The following morning, while dew was still present, a greens mower was driven through the perennial ryegrass and across the adjacent creeping bentgrass. When evaluated 5, 10, and 25 d after treatment, visible track length and creeping bentgrass injury were greatly reduced by irrigating perennial ryegrass 2 h after treatment or by irrigating both perennial ryegrass and creeping bentgrass prior to simulated mowing. Visible injury of tracked turfgrass persisted for 36 d after treatment when irrigation was not applied and for as few as 5 d when both perennial ryegrass and creeping bentgrass were irrigated. Irrigation had no effect on perennial ryegrass control. Gibberellic acid at 0.12 kg ai/ha and foliar iron at 1.3 kg ai/ha, applied when tracks first appeared, did not improve the recovery of injured creeping bentgrass. Our results suggest that when applying rimsulfuron near susceptible bentgrass, the lowest effective rate should be applied and that the bentgrass should be irrigated at least 2 h after treatment to prevent nontarget injury.

The Sheyenne National Grassland (SNG) is a native tall grass and mixed grass prairie located in southeastern North Dakota. Approximately half of the SNG has been invaded by leafy spurge (Euphorbia esula L.) and control methods have been limited. Many herbicides cannot be utilized at the SNG due to sandy soils (> 80%) and shallow groundwater, nor can they be applied near the western prairie fringed orchid (Platanthera praeclara Sheviak and Bowles), a federally listed threatened plant found on the SNG. Quinclorac and aminocyclopyrachlor were considered for use on the SNG but potential to enter the groundwater was unclear. Movement of quinclorac and aminocyclopyrachlor was evaluated in 70 cm soil columns that simulated field conditions from five ecological sites. Quinclorac leached further following the heavy rainfall event of 15 cm in 48 h compared to the annual precipitation of 51 cm applied over 9 wk. Quinclorac leached approximately 45 cm into the soil profile averaged over all soil types and both precipitation events but never exceeded 65 cm regardless of soil type. Aminocyclopyrachlor leaching was greater than quinclorac and moved through all soil types into the leachate following both watering regimes. Desorption of both herbicides was incomplete. Approximately 10 and 32% of applied aminocyclopyrachlor and quinclorac, respectively, remained in the top 5 cm of soil regardless of soil type or watering regime. Quinclorac but not aminocyclopyrachlor was considered suitable for use at the SNG to control leafy spurge and has the added benefit of not harming the western prairie fringed orchid.

Amicarbazone and indaziflam are relatively new herbicides that provide effective control of important weed species in turfgrass. A concern for golf course superintendents and turfgrass managers is the lack of information about runoff risk of these two herbicides, which is a limitation to their proper and safe use. The objectives of this research were (1) to compare lateral movement in surface soil of amicarbazone and indaziflam to other commonly used PRE herbicides in turfgrass (i.e., dithiopyr, prodiamine, pronamide, simazine) and (2) to determine whether incorporating the herbicide with irrigation before a simulated storm event reduces lateral movement. Herbicides were applied at full label rates in two locations (Jay and Milton, FL) with 14% slope, and lateral movement was evaluated using perennial ryegrass and annual bluegrass as bioindicators. Incorporating PRE herbicides with irrigation a few hours before a major simulated storm event did not reduce lateral movement of any of the herbicides evaluated. All herbicides moved outside the treated area regardless of the presence of a simulated storm event. Herbicide lateral movement varied from 61 to 153 cm in Jay, and from 5 to 103 cm in Milton. The Milton location had higher sand content and lower organic matter content than Jay, which favored water infiltration. No herbicide effects were observed 210 cm downslope from the treated area. On the basis of our results, the ranking from highest to lowest lateral movement was pronamide > simazine ≥ indaziflam > amicarbazone ≥ dithiopyr > prodiamine. The difference in lateral movement was approximately 60 to 80 cm between pronamide and prodiamine depending on location and evaluation timing for the 14% slope at the study sites. The results of the present study provide guidance for golf course superintendents and turfgrass managers to determine buffer zones in sensitive areas.

Several field observations and limited research have confirmed that sulfonylurea herbicides commonly used in warm-season turf can laterally relocate via turf equipment and injure neighboring cool-season grasses. This phenomenon is referred to as ‘tracking’ among turf managers and often occurs when mowers traverse treated areas and adjacent creeping bentgrass putting greens, fairways, and tee boxes while foliage is wet with dew. Tracked flazasulfuron and metsulfuron at 9 and 42 g/ha, respectively, caused little injury to creeping bentgrass. Flazasulfuron at 26 and 53 g/ha, and foramsulfuron at 28 g ai/ha tracked while dew was present 20 h after treatment (HAT) resulted in the most noticeable creeping bentgrass injury when tracked. Flazasulfuron at higher rates and foramsulfuron tracked 20 HAT on dew-covered turf reduced turf color compared to nontracked turf. When the mower traversed dry turf at 6 HAT and wet turf at 68 HAT, turf color was reduced less than wet turf tracked 20 HAT. Length of track and creeping bentgrass injury decreased with flazasulfuron rate. When using flazasulfuron at rates between 9 and 53 g/ha, a 1.5- and 4.5-m border, respectively, around creeping bentgrass would eliminate most injury from tracked herbicide.

Diuron, simazine, and terbacil were applied in field plots annually from 1981 to 1995. Soil was sampled at selected times after herbicide application in 1993, 1994, and 1995 to determine herbicide residue changes with time and soil depth. Diuron residues were found mainly in the upper 20 cm of soil; residue concentration decreased exponentially with time. Less than 1% of the initial concentration after application in summer was present the following spring. Terbacil residues were found in soil below the upper 20 cm. Terbacil degraded more slowly than diuron, and residues in spring were less than 30% the level of the previous summer. Simazine plus hydroxysimazine soil residues were present in all depths to 100 cm and were higher than diuron or terbacil at these depths. Simazine plus hydroxysimazine residues in spring were nearly 40% the level of the previous summer. With all three herbicides, soil residues were greatest in the upper 20 cm of soil during 2 to 3 wk following application. Data confirmed that diuron did not leach, whereas simazine can migrate through the soil. Terbacil migrated intermediately in depth relative to diuron and simazine. After 15 annual applications, herbicide residues were present but were not accumulating.

Herbicide soil/solution distribution coefficients (Kd) are used in mathematical models to predict the movement of herbicides in soil and groundwater. Herbicides bind to various soil constituents to differing degrees. The universal soil colloid that binds most herbicides is organic matter (OM), however clay minerals (CM) and metallic hydrous oxides are more retentive for cationic, phosphoric, and arsenic acid compounds. Weakly basic herbicides bind to both organic and inorganic soil colloids. The soil organic carbon (OC) affinity coefficient (Koc) has become a common parameter for comparing herbicide binding in soil; however, because OM and OC determinations vary greatly between methods and laboratories, Koc values may vary greatly. This proposal discusses this issue and offers suggestions for obtaining the most accurate Kd, Freundlich constant (Kf), and Koc values for herbicides listed in the WSSA Herbicide Handbook and Supplement.