Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
I have had very interesting conversations with growers, fieldmen, consultants, and extension staff about lima beans recently. There is a wealth of experience with this crop to be mined with the long history of production in the region.
One of the curiosities has been with how lima beans respond to cultivation. Growers have noted that after each cultivation lima beans really “jump”, going through a growth spurt. One of our consultants has noted that lima beans are one of the most responsive vegetable crops to cultivation. Yields are often increased by as much as 30% with cultivation. Is this related to plant responses to increased soil aeration, looser soil and better soil exploration by roots, or other factors? We don’t really know. We also do not know if some varieties are more responsive than others. However, this has implications for trying to grow high yielding lima beans in reduced tillage or no-till situations.
Past experience with no-till has shown that even with good weed control, yields are lower than conventional systems with cultivation, especially after small grain. Vertical tillage is also a common practice now and growers are interested in using these tools ahead of lima bean production in reduced tillage systems. However, the same problem applies, without cultivation, yield potential is lost. Use of cultivators designed for high residue and no-till situations can recover yield potential in such fields but you have now lost the advantage of no-till (reduced trips across the field, no soil disturbance). In addition, weed control can be a challenge in no-till and reduced tillage lima bean plantings.
A question we will be asking in our Extension and breeding programs and of growers is: Should we invest time and effort into testing breeding material for better adaptation to no-till and reduced till situations?
An additional curiosity with cultivation has been that late cultivation is often advantageous, even if some damage is done because it opens up the crop to better aeration and in varieties that produce runners, removes the runners, concentrating set on the upright part of the plant. Little if any yield is lost with late cultivations. While several of our newer varieties (Cypress, Meadow, Maestro) do not runner much others such C-elite Select and 184-85 do produce some runners. It is interesting to note that in the past with varieties with heavy runnering, the common practice was to cut the runners off with discs.
Another curiosity is how lima beans respond to irrigation. While highest yields have been obtained in irrigated production, lima beans can be very productive in dryland plantings. Over-irrigation or improper irrigation of lima beans has caused increased pod disease pressure and seed quality issues (brown beans). Lima beans respond best to less frequent, heavier irrigations and need a greater drying period than other crops for disease management. More frequent, light irrigations can actually reduce yield.
Another curiosity is the great ability of lima beans to regrow after a harvest. The potential for a two-harvest system is there if we can get a better adapted, heat tolerant, early maturing variety to work with.
A final curiosity that we have seen in May plantings most years and in June plantings in years with very hot July and early August temperatures is that lima beans will drop most if not all immature pods, flowers, and buds if day temperatures exceed the mid-90s and night temperatures are high. In some years, harvest is delayed by 2-3 weeks because the first sets have been dropped. In other years, severe split sets occur. We have a narrow genetic base in the varieties that are currently available and they are not well adapted to our heat. To address this, efforts are underway to cross and select with heat tolerant types from the Caribbean, and the southern and southwestern U.S.