Department of Horticulture, Iowa State University
An interesting plant sample came in yesterday from one of the snap bean growers from Hancock County, Iowa. Apart from the description of a potential disease, which the plant diagnostic lab will figure out soon, the information sheet also contained a note: "The crop flowered profusely but is not bearing any pod". Pictures below show few to almost no pods on the plant.
This unusual event is called "Blossom-Drop" which is quite common in peppers, snap beans, and tomatoes. There are multiple causes for this to occur such as dry windy conditions, excessive use of nitrogenous fertilizers, but the most common cause is high temperature. Tomatoes, peppers and beans are sensitive to prevailing air temperatures with regard to setting fruit. When the day temperatures are above 90 degrees, it affects pollen viability and thus adversely affects pollination. If the flower isn't pollinated, it dies and falls off.
Another important aspect to consider is irrigation. Green beans are particularly susceptible to blossom drop under water stress. Growers should carefully monitor crop water requirement and irrigate whenever needed (depending upon soil type). For growers confronting 'blossom drop', there will be some yield reduction but when temperatures turn cooler new flowers form which would set new pods.