Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu
The earliest processing lima beans will be planted starting in the next 10 days. May planted lima beans often have a lower yield potential than June and early July plantings due to a number of factors. Soil conditions may be cold and this delays germination and reduces stands. Minimum soil temperature for best germination is 65°F. Soil borne diseases, such as Rhizoctonia and Fusarium, can become established on plant roots, especially when they are growing slowly in cold soils. This can limit the later yield potential of these early planted lima beans. Also, heavy infestations of seed corn maggot can overwhelm seed treatments in cold, wet soils reducing stands.
The major limiting factor for early lima beans is the fact that they flower and set pods during summer conditions when day and night temperatures are high. Low lima bean yields in early plantings are associated with high levels of flower and pod drop. Hot, dry weather in July and August will lead to reduced pod set and retention. Day temperatures of 90°F or above reduces pollination and pod set and night temperatures in the 70s or higher will also adversely affect yields because higher levels of carbohydrates are consumed in night respiration, limiting the plants ability to set and retain pods. Plants may reflower when cooler conditions recur, leading to split sets.
Split set in lima bean
The following are some considerations for early lima bean plantings:
- Plant in fields with light soils that heat up quickly and where emergence will not be delayed. Conventional tillage is required for early plantings to speed this warming.
- Plant on a warming trend when soils are 65°F or higher.
- Consider using an additional fungicide treatment for Rhizoctonia control (Ridomil Gold PC or Quadris).
- Choose fields carefully. Fields closer to water bodies were temperatures are moderated by fog, heavy dew, high humidity, and cooling breezes during summer are good candidates.
- Irrigate early planted fields, paying particular attention to the flowering and early pod set period. Daytime irrigation can also help to moderate high temperature effects during hot summer periods. It is critical to keep early planted lima bean plants from being water stressed during this period. Do not plant early lima beans dryland.
Although success in early lima bean plantings can be improved by following these suggestions, if there are extended periods with day temperatures in the 90s and night temperatures in the high 70s, yields will still be limited.