Optimizing Row Spacing and Seeding Rate for Improved Pinto Bean Agronomic Performance Under White Mold Disease Pressure

Planting pinto beans to narrow rows is known to maximize pinto bean yields in the absence of white mold, but worries about white mold have limited the adoption of narrow rows.

In 2019 and 2020, the plant pathology program at the Carrington Research Extension Center, in conjunction with the agronomists at the Robert Titus Research Farm in Oakes, evaluated the impact of seeding rate and row spacing on agronomic performance of pinto beans under white mold disease pressure. Testing was done with ‘Palomino’ and ‘Vibrant’ slow-darkening pinto beans. To assess the impact of row spacing and seeding rate under different levels of disease pressure, testing was done with no foliar fungicide, with a single fungicide application at early bloom (Topsin at 40 fl oz/ac), with two sequential fungicide applications (Topsin at 40 fl oz/ac followed by Endura at 8 oz/ac), or with pinto beans seeded into a rye cover crop terminated either 10-14 days before planting or 0-3 days after planting. Plots were 10 feet wide and 25 feet long, with the middle 5 feet by 20 feet harvested for yield. All studies were conducted with six experimental replicates. Overhead irrigation was applied as needed to create conditions favorable for white mold. White mold was assessed shortly before or at maturity. Within each plot, a third to half of the plants were individually assessed for white mold severity.

The row spacing that optimized pinto bean agronomic performance was contingent on white mold disease pressure (Figure 1).

Photo Credit:

Michael Wunsch

Figure 1. Impact of row spacing on white mold severity and yield in pinto beans. Data are from studies conducted in Carrington and Oakes, ND in 2019 and 2020 with no foliar fungicide, one or two fungicide applications, fallow ground, direct-seeded into winter rye terminated 10-14 days prior to planting, or direct-seeded into rye terminated 0-3 days after planting. Within-column means followed by different letters are significantly different (P < 0.05; Tukey procedure).

When white mold pressure was low to moderate (less than 20% in 30-inch rows), pinto bean yield was maximized in narrow (7.5- or 15-inch) rows. The yield gain associated with earlier canopy closure and the resulting increase in photosynthesis was greater than the reduction in yield associated with the modest increase in white mold pressure associated with narrower rows. When white mold pressure was high (more than 20% in 30-inch rows), pinto bean yield was similar across row spacings, and pinto bean agronomic performance was optimized in wide (30-inch) rows. Disease was lower in the 30-inch rows, and the reduction in white mold observed in wide rows reduced seed quality problems (primarily moldy seed and sclerotia contamination).

Planting pinto beans at 70,000 viable seeds per acre optimized agronomic performance under white mold pressure (Figures 2 and 3).

Photo Credit:

Michael Wunsch

Figure 2. Impact of increasing seeding rate from 70,000 to 120,000 viable seeds/ac on white mold severity and yield in pinto beans. Data are from studies conducted in Carrington and Oakes, ND in 2019 with no foliar fungicide, one or two fungicide applications, fallow ground, direct-seeded into winter rye terminated 10-14 days prior to planting, or direct-seeded into rye terminated 0-3 days after planting. Within-column means followed by different letters are significantly different (P < 0.05; Tukey procedure).

Photo Credit:

Michael Wunsch

Figure 3. Impact of increasing seeding rate from 70,000 to 90,000 viable seeds/ac on white mold severity and yield in pinto beans. Data are from studies conducted in Carrington, ND in 2020 with no foliar fungicide, one or two fungicide applications. Within-column means followed by different letters are significantly. different (P < 0.05; Tukey procedure).

Increasing seeding rate to either 90,000 or 120,000 viable seeds per acre had little impact on yield but was consistently associated with higher white mold disease pressure.

The research suggests that pinto bean seeding rate should be kept to 70,000 viable seeds/ac in fields where white mold is a concern. The optimal row spacing changes as disease pressure increases, with narrow (7.5 and 15-inch) rows optimal when white mold pressure is low to moderate and wide (30-inch) rows optimal when white mold pressure is high.

Research conducted by M. Wunsch, Thomas Miorini, Suanne Kallis and Jesse Hafner (NDSU Carrington Research Extension Center) and Kelly Cooper, Heidi Eslinger, and Seth Nelson (NDSU Robert Titus Research Farm in Oakes).

Michael Wunsch, Ph. D.
Michael.Wunsch@ndsu.edu
Plant Pathologist