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The bean fly (Agromyza phaseoli) is a pest of French beans during summer and autumn in coastal New South Wales especially. It sometimes occurs in north western districts such as Gunnedah and Morce. Both bush and climbing beans are attacked whilst late sown cowpeas and soybeans may also be infested. Broad beans are not injured.
The small black flies lay their eggs in the bean leaf tissue and heavily attacked leaves may be " peppered " with the small egg-laying punctures. The maggots which hatch from these eggs after about two days mine in the leaf tissue for a short time and then tunnel down the leaf stalks, finally making their way down into the stem. There they feed and destroy the inner tissues of the stems causing the plants to wilt and finally fall over and die. In lighter infestations the stems become swollen and cracked and the plants may become yellow and severely dwarfed and susceptible to being blown over by wind.