Research was conducted to determine the effects of management practices and precipitation on herbicide loss in surface water runoff. A field runoff experiment was conducted in 1999 and 2000 in Manhattan, KS. Some plots received only natural precipitation, whereas others received natural precipitation plus additional precipitation from a rainfall simulator. Atrazine was applied at 0.9 and 1.8 kg ha−1, S-metolachlor at 0.7 and 1.4 kg ha−1, and isoxaflutole at 0.05 and 0.11 kg ha−1 to field corn grown under conventional tillage and no-till. Runoff volumes and herbicide concentrations were determined for each runoff event. Across all precipitation, tillage, and placement variables, atrazine, S-metolachlor, and isoxaflutole and diketonitrile (DKN) (soil metabolite of isoxaflutole), hereafter referred to as isoxaflutole/DKN, losses were similar at 5.0, 4.1, and 4.1% of applied, respectively. Additional precipitation increased runoff 2.5-, 2.2-, and 3.4-fold for atrazine, S-metolachlor, and isoxaflutole/DKN, respectively. Preplant soil incorporation reduced atrazine, S-metolachlor, and isoxaflutole/DKN losses in runoff by 67, 69, and 57%, respectively, compared with soil surface applications. Lower preplant rainfall in 2000 resulted in sharply reduced runoff losses despite postplant precipitation similar to that in 1999. These findings suggest that the best management practices for atrazine can be used to manage S-metolachlor and isoxaflutole/DKN loss in surface water runoff.

BACKGROUND: There is renewed interest amongst crop protection professionals and regulators in the adoption of spray hoods to further reduce pesticide off-target movement during applications. Although the benefits of sprayer hoods have been reported since the early 1950s, adoption has been relatively low among farmers and applicators. The objective of this study was to evaluate the effectiveness of spray hoods in reducing pesticide drift of spray solutions from nozzles typically used for herbicide applications in row crops with tolerance to dicamba or 2,4-D.RESULTS: Hooded applications substantially reduced spray drift potential across all treatment scenarios compared to conventional applications. Hooded applications using the AIXR nozzle without drift-reducing adjuvant (DRA) had a similar area under the drift curve (31.5) compared to conventional applications (open sprayer) using the TTI nozzle with DRA (27.7), despite the major droplet size differences between these treatments (D V50 = 447.5 and 985 ∼m, respectively).CONCLUSION: These results indicate that the adoption of spray hoods combined with proper nozzle selection, and the use of DRAs can substantially reduce spray drift potential during pesticide applications. The use of this technology can be complementary to other drift-reducing technologies.

Field experiments were conducted from 1996 to 2000 near Manhattan, KS, to determine the effects of application timing on atrazine loss in surface water runoff. In addition, Groundwater Loading Effects of Agricultural Management Systems (GLEAMS) was run to compare simulated loss with actual loss in the field. Atrazine treatments were fall plus preemergence (FALL + PRE), early preplant plus PRE (EPP + PRE), PRE at a low rate (PRE-LOW), and PRE at a full (recommended) rate (PRE-FULL). Ridge-till furrows served as mini watersheds for the collection of surface water runoff. Water runoff volumes and herbicide concentrations were determined for each runoff event. Across four sampling years, mean atrazine runoff loss was 1.7, 4.3, and 1.7% of applied for FALL + PRE, EPP + PRE, and the mean of the PRE treatments, respectively. Thus, actual average losses from FALL + PRE and EPP + PRE treatments were somewhat higher than that predicted by GLEAMS. For PRE treatments, actual average losses were significantly lower than that predicted by GLEAMS, with measured losses falling below the bottom of the graph in 3 of 4 yr. These findings suggest that in certain parts of the Great Plains, FALL + PRE split applications of atrazine offer acceptably low atrazine runoff loss potential; EPP + PRE is more vulnerable to loss than FALL + PRE; and the GLEAMS model may overestimate atrazine runoff potential for PRE applications.

The front cover image is based on the Research Article Hooded broadcast sprayer for particle drift reduction by Bruno Canella Vieira et al., https://doi.org/10.1002/ps.6770.