Dry beans can be planted from mid-May to early June in Manitoba. This later planting period protects seedlings from post-emergent frost damage, which can injure dry bean seedlings and reduce plant stand. According to MASC data from 1989-2008, the second, third and fourth weeks in May produce the greatest navy bean yields in Manitoba.
Recent planting date research in North Dakota has shown that typical late May to early June planting dates for all dry bean market classes remain appropriate for optimum yield potential and reduced frost risk. From 2012 to 2015, pinto, black and navy bean beans yielded similarly between early (May 11-24), normal (May 22-June 5) and late (June 5-18) planting dates (Table 1). A trend toward higher yields for normal and late planting dates was observed, although this was not significant.
Like other large-seeded crops (i.e., field peas, soybeans), dry beans can withstand greater seed depth than small-seeded crops (i.e., canola, cereals) to ensure they have adequate seed to soil moisture contact. The recommended seeding depth range is 0.75 inches to 2 inches, depending on the market class. Plant at a slower speed to minimize dry soil in the furrow and ensure adequate down pressure to achieve the desired depth.
Target Plant Stand and Seeding Rate
Target plant stands vary among dry bean market classes and row spacings. Calculate seeding rates (seeds/ac) to establish the target plant stands (live plants/ac) listed in Table 2. Factor expected seed survival into seeding rate calculations. Also consider economic factors such as seed cost, expected grain price and yield.
Conduct a soak test to assess seed damage:
Place 200 seeds in water and calculate the percentage of seed coats that slough off. Factor this percentage into seeding rate calculations. Seeds that lose their seed coats may produce a “bald head” seedling that emerges without cotyledons and does not produce a viable plant (Figure 1).
Research led by Dr. Rob Gulden lab at the University of Manitoba examining plant density and row spacing has shown that dry bean yield is relatively insensitive to changes in plant population. This result is from four years of testing. The study is ongoing to explain the lack of dry bean yield response and to identify optimal target plant stands of dry beans in Manitoba.
Dry bean plant stand can impact pest pressure. Beans are a poor competitors against weeds. Reducing plant populations below the recommended target plant stands can negatively impact the competitive ability of the crop. Low plant populations are more susceptible to weed pressure and weed management concerns. Dr. Gulden’s research has shown that high plant populations conversely increased white mould severity, even when a fungicide was applied.
Row spacing is another management tool that can assist with crop competition against weeds. Dry beans have traditionally been planted in wide rows to promote airflow in the crop canopy to prevent disease development (e.g., white mould). However, recent research conducted in Manitoba and Saskatchewan has pointed to yield benefits associated with narrow rows. This is due to faster crop canopy closure that out-competes later flushes of weeds and captures sunlight better.
Preliminary results from Dr. Gulden’s lab (U of M) have shown that the combined average yields of pinto and navy beans declined with wider row spacing. Row spacing of 7.5 inches yielded 1.8 times greater than the more common 30-inch rows. Similar results were reported by Jeff Ewen (Saskatchewan Ministry of Agriculture) who also conducted research comparing narrow- vs. wide-row beans. Under dry conditions, narrower rows may also provide the added benefit of moisture conservation. However, growers must also be aware of the increased risk of seed damage that can result from air seeders and seed handling.