In the UK Seed Certification Scheme, seed is graded as Basic (B), Certified Seed of 1st Generation (C1), and Certified Seed of 2nd Generation (C2). Basic and C1 seed is generally grown for the production of further seed crops and C2 seed is used for commercial crop production. Basic seed is the most expensive and C2 the least expensive. Certified seed is required to meet a minimum germination of 80% and to achieve a standard of purity.
Seed-borne leaf and pod spot (Ascochyta fabae) and stem nematode (Ditylenchus spp.) can be very damaging to field beans. It is strongly recommended that seed is tested for Ascochyta. It is advised that Basic seed should not contain more than 0.2% infection, C1 seed should not contain more than 0.4%, and C2 seed should not contain more than 1% infection. It is also strongly recommended that seed is tested for the presence of stem nematode and only clean seed should be used. Seed tests are available from PGRO. There are currently no seed treatments available for use in field beans.
There is growing interest in direct drilling or minimum tillage drilling of both winter and spring beans. There is an advantage in the min-till system for spring beans where over- wintered stubble is part of the farm management scheme.
Winter beans can be broadcast or drilled onto the soil surface and then covered by shallow ploughing. However, both seed distribution and seedling emergence can be very uneven. Most winter beans are now drilled. Winter beans should not be sown too early - not before the second week of October. Crops which are too forward are more prone to disease and to the effects of severe winter weather. Sowing from mid-October to early November is usually the optimum time, but acceptable crops have been produced from early December drilling. Winter beans can be sown in the early spring. They should be treated as a spring bean, increasing the plant population to 36-40 plants/m2.
Spring beans are best drilled as early as possible from late February onwards provided soil conditions are satisfactory. Later sowing delays harvest and may subject beans to summer drought stress at flowering. Ploughing-in is not common nowadays as it is less successful for spring beans, and better yields are achieved where they are drilled conventionally. Sowing depth is important and the seed should be covered by a minimum of 3cm of settled soil where pre-emergence herbicides are used.
For spring beans, recent data from the Optibean project shows that maximum yields are obtained from 60-65 plants/m2. But when taking into account seed cost and produce value, the economic target population is 50-55 plants/m2. This is for soils/areas that produce typical bean growth. For fertile soils or areas that produce very vigorous growth, target populations should remain at 35-45 plants/m2. Field loss for winter beans is expected to be 15% and for spring beans 5%. PGRO has produced a seed rate calculator as part of the Optibean tool (Excel based spreadsheet) and is available from the PGRO website.
The seed rate can be calculated from the following formula: