Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu
Both early planted processing baby lima beans and market garden pole lima beans are showing signs of nitrogen deficiency now across the state, even with adequate N being applied. This is likely a result of excessive N leaching during the wet spring periods in May and early June in many fields, especially on very sandy soils. Pole lima beans commonly show N deficiencies later in mid-summer as pod set and development progresses; however this year, yellow plants are being seen much earlier.
Severe N deficiency in lima beans will be seen as an overall yellowing of plants with lower leaves often dropping off as N is mobilized from the oldest leaves to support the new growth at growing tips. Less severe N deficiency will be seen as a lighter green color than normal with lowest leaves most affected. Tissue tests can be used to confirm N deficiencies. Take the uppermost fully expanded leaves to send off for analysis. There are other potential causes for yellowing in lima beans including low pH leading to magnesium deficiencies and excessively high pH leading to micronutrient deficiencies, most commonly manganese.
It is important to apply additional N as soon as possible in N deficient lima beans. General recommendations are to sidedress 30-40 lbs of N, 3-5 weeks after emergence in baby lima beans and at early pod set in pole lima beans. In fields that have suffered heavy leaching losses, this may need to be increased slightly. However, remember that too much N can lead to excessive vine growth and delay flowering and pod set. Deficient pole lima beans will need an early sidedress application now and will likely need an additional sidedressing of N in August during pod development.