The field study is being conducted at the NDSU Carrington Research Extension Center with support from the ND Soybean Council and Northarvest Bean Growers Association. Study objective is to evaluate soybean, pinto bean and sunflower plant growth and seed yield response based on timing of planting following application of preplant, low-dose soil rate of dicamba with or without water activation. Experimental design was a randomized complete block with a split-plot arrangement (main plot=crop; split plot=herbicide; and split-split plot=planting date) and four replications. The irrigated trial was established with field pea as prior crop on conventional-till Heimdal-Emrick loam soil with 3.9% organic matter, 7.6 pH, 41 ppm P, 312 ppm K, 2.01 ppm Zn, and 0.45 mmho/cm soluble salts (0- to 6-inch depth). Dicamba (Clarity at 4 fl oz/A [0.125 lb ai/A]) was soil applied with a CO2-hand-boom plot sprayer delivering 17 gal/A at 35 psi through TJ Turbo 02 nozzles to the center 6.7 ft of 10- by 25-ft plots on May 13 with 44 F, 63% RH and 5 mph wind to wet soil surface. Planting dates were May 19 and June 1; 6 and 19 days, respectively, following application of dicamba. Crop cultivar and targeted stands: soybean - Peterson Farms Seed ‘19B04’ and 150,000 plants/A; pinto bean - ‘ND Palomino’ pinto bean and 70,000 plants/A; and sunflower - Mycogen ‘8N270CLDM’ and 20,000 plants/A. Crops were planted in 30-inch rows. Irrigation and rainfall totaled 0.08 inch between application of dicamba and the first planting date; and 2.16 inches between application of dicamba and the second planting date; and 22.5 inches June 1-Sept. 29. Seed harvest with a plot combine occurred on the following dates: pinto bean = Sept. 9 (plants hand-pulled and placed in swathes Sept. 7); soybean = Oct. 4; and sunflower = Nov. 1.
Soybean plant stand (trial average=119,500 plants/A) was similar among treatments (Table 1), though the density tended to be reduced with early planting following application of dicamba. Plant development, height and canopy closure generally were not impacted by dicamba. Plant injury with early planting after application of dicamba was 32-43% when evaluated during the first 4 weeks after plant emergence but declined over time. Minimal (4-5%) or no plant injury was observed with the late planting date following application of dicamba. Seed yield was excellent and did not differ among treatments. Seed test weight and count also were not negatively impacted by dicamba.
Pinto bean plant stand, averaging 77,500 plants/A, was similar among treatments (Table 2). Plant development, height and canopy closure were not impacted by dicamba. Plant injury with early planting after application of dicamba was 14-28% when evaluated during the first 4 weeks after plant emergence but declined over time. Minimal (7%) or no plant injury was observed with the late planting date following application of dicamba. Seed yield, test weight and count were not negatively impacted by dicamba.
Sunflower plant stand, averaging 25,900 plants/A, was similar among treatments (Table 3). Plant development, height and canopy closure generally were similar among treatments. Plant injury was essentially absent following application of dicamba. Also, seed yield and test weight were similar among treatments.
