Bean plants grow during the warm summer months, and are popular for home gardens. Most bean varieties prefer light to sandy well-drained soil. Garden grown bean plants typically have hearty growth of 24 to 30 inches tall. However, maintenance issues, soil quality, and diseases can cause yellowing of bean plants, given the right conditions.
According to the Soil Science Education website operated by NASA, plants lacking sufficient nitrogen levels have yellowish-green leaves, thin stems, and stunted growth. Nitrogen, vital for plant growth, is one of the primary macronutrients found in soil and fertilizer. Nitrogen helps plants with cell division and leafy green growth. University-based or private labs can test nitrogen levels in soil to determine the proper application of fertilizer.
Underwatering and overwatering of bean plants can cause yellowing and blossom and pod drop. According to Purdue University, bean plants need 1 inch of water per week in well-drained soil. Overwatering can cause misshapen bean pods, crop loss, and disease susceptibility. However, yellowing of the bean plant occurs when the plant does not absorb enough water.
Bean rust, caused by the bacterium Uromyces phaseoli var. typica, is a serious bacterial infection that affects many bean plant varieties. The bacteria thrive in humid, moderate temperatures and can cause substantial crop loss, states the University of Connecticut. The rust turns infected bean plants a yellow to brown color, and can cause defoliation. Chemical defoliant is the most common solution, but greatly reduces crop yield, because it kills all foliage on the plant.
Bean Yellow Mosaic Virus
The bean yellow mosaic virus (BYMV) is one of the most common diseases in all bean plant varieties. BYMV spreads from aphids, a small plant-eating insect also known as plant lice. A leaf mosaic with contrasting yellow areas identifies the virus. BYMV typically does not reduce crop yield, but can reduce the number of seeds in each bean pod. BYMV is not a seed-borne virus and can be controlled with chemical pesticides that target aphids before infection occurs.
Bacterial Bean Blight
Bacterial bean blight, caused by the bacterium Xanthomonas phaseoli, is a common bacterial infection in bean plants. The bacteria thrives and reproduces in warm, humid conditions, states the Cornell University Department of Plant Pathology. Symptoms of bacterial blight consist of brown, dry tissue with a yellow border on leaves, lesions on leaf margins, and circular spots. Infection occurs on seeds, and has no noticeable symptoms until germination.