Desiccation

Desiccation is common practice in dry bean production for uniform dry-down and weed control, but it does not bring about or speed up maturity. See below for dry bean desiccation timing and pre-harvest weed control and desiccation products.

Timing 

Proper desiccation timing is critical to prevent yield and quality loss, and residue accumulation in the seed. Dry bean crops are ready for desiccation at 80% pod colour change and 80 to 90% leaf drop (Figure 1). Plants at that point are physiologically mature and seed moisture is <30%.

Below: Field view of dry beans at various stages of pod colour change (PCC). Total days elapsed is 10-14 days.

 

 

Products

Products available for desiccation in dry beans include Heat (saflufenacil), Reglone (diquat) and Valtera (flumioxazin), which can be used alone or in combination with glyphosate. Using tank mixes rather than glyphosate alone can improve weed desiccation and prevent glyphosate residue accumulation in the seed. However, some buyers have already made the decision to not accept dry beans sprayed with pre-harvest glyphosate. It is important to consult your local buyer and keepingitclean.ca/pulses before selecting a pre-harvest or desiccation product to avoid market risks.

Harvest Methods

Dry beans can be harvested by undercutting and windrowing, swathing or direct harvesting (i.e., straight combining). Cutting and windrowing is more common for row-cropped beans and vine-type varieties that pod low to the ground. Direct harvest or swathing with lifters prior to combining has been more common for solid-seeded beans and bush-type varieties that achieve greater pod heights.

Undercutting & Windrowing

More common in Manitoba, especially for pinto and specialty beans. It uses a long (~3ft) knife and requires a soil ridge to successfully cut plants. The ridge is often created by inter-row cultivation, relating weed control to harvest techniques. Plants can be pulled from the soil and windrowed as one operation, or they can be cut below the soil line and windrowed in two operations. Windrows are then combined. There is a risk with this harvest method that heavier soil and mud balls remain attached to the root if it is pulled out of the soil rather than cut.

Swathing

Used by some farmers in Manitoba. Swathing often occurs at an angle and occurs when minimal leaf material is left on the plant, due to the mould issues leaf material could cause in the swath. Dry bean crops that are swathed are not typically inter-row cultivated.

Direct Harvesting (i.e., straight-cutting)

Often used for navy and black bean crops and most row cropped beans in Manitoba. Other bean growers may also be interested, as this method is less labour-intensive. Desiccation is usually required to dry down green plant material and control weeds. Beans are then direct harvested 7-10 days later. Direct harvesting dry beans requires flat soil that has not been inter-row cultivated. When direct harvesting, there is a greater risk of loss at the cutter bar due to pod shatter and low pods that are left behind.

Research

MPSG-funded research has evaluated the impact of dry bean plant architecture on harvest losses associated with undercut vs. direct harvest methods. In this study, yield differences between the two harvest methods were compared across varieties.

Surprisingly, variety (i.e., plant architecture) had no impact on yield differences between harvest methods in three out of four years. In other words, the characterized plant architecture of dry bean varieties should not be the only factor that dictates which harvest method is chosen. In the year that significant varietal differences were observed (2014), undercutting of pinto beans was superior to direct harvest. Under the moist conditions of 2016, undercutting was superior to direct harvest for all varieties.

Overall, it is recommended to assess how the growing season impacts plant architecture and choose the best method of harvest accordingly (e.g., undercut if plants are lower to the ground, direct harvest if plants remain upright). It is also advised to select an upright variety for its yield potential, rather than suitability to direct harvest.

General Harvest Tips

• Dry bean harvest can begin at 16-18% seed moisture. This is when some pods are brown, but most pods are still yellow. If the timing is right and pods are very dry, aim to cut when there is dew to avoid shatter losses.
• Constant feeding into the header can reduce losses. Areas with less plant material may cause poor feeding into the header and therefore losses.
• High cylinder speeds and augers can inflict the greatest amount of seed damage. Set cylinder speeds as low as possible and to minimize seed damage.
• The maximum safe storage moisture for dry beans is 16%. Moisture content below 16% can increase the amount of split or cracked seed coats and shriveled beans. Beans above 17% moisture are at risk of heating and spoilage.
• Visit the Canadian Grain Commission for a list of bean grade determinants.

Additional Resources

Successful Desiccation Decisions in Peas and Beans – Pulse Beat (Issue 90) article by Cassandra Tkachuk, MPSG
The Science and Art of Dry Bean Desiccation – Crops and Soils Magazine (2016) article by Jeanette Gaultier and Rob Gulden
Edible Bean Harvest Methods by Variety – Pulse Beat (Issue 76) article, On-Farm Network
Manitoba Agriculture – Field Bean – Production – Harvest Management