Q What is black bean aphid?
A Also known as blackfly, Aphis fabae, is the most serious pest of broad beans but also attacks French and runner beans later in the summer and ornamentals, including dahlias, poppies and nasturtiums. It overwinters on shrubs such as euonymus, Viburnum opulus and philadelphus.
Caption: Broad-bean aphids can seriously weaken the plant by sucking the sap
Q Does black bean aphid cause serious damage?
A A single winged female landing on a broad bean plant from May onwards can create a large colony very quickly, thanks to their prodigious reproductive rate. Live young can in turn give birth within a week as temperatures rise.
Ants farm and protect the colonies and can spread the infestation further. Each aphid punctures the stems of the plant and feeds on the sap. Severe attacks can seriously weaken the plant and the sticky honeydew excreted as a waste product encourages surface moulds.
Q How do I control black bean aphid?
A Black-bean aphids are relatively easy to kill with a contact insecticide based on pyrethrum, or fatty acids if you prefer an organic option, or synthetic pyrethroids. Repeat spraying may be necessary (follow the instructions) to finish off any survivors. Predators such as ladybirds, lacewing and hoverfly larvae, if present may help but are unlikely to be able to keep up with a rapidly expanding colony. Use insecticides in the evening to avoid harming bees.
Q Are there any non-chemical options for black bean aphid?
A One approach is to inspect the crop twice weekly from May onwards, paying particular attention to the growing tips. Individual blackfly can be squashed and small colonies can be removed by pinching out the growing tip. Take care to remove every aphid, since survivors will continue to multiply. Once four or five flower trusses have formed pinching out all tips will remove the most tempting part of the plant for aphids and concentrate the plants' efforts on producing pods.
Caption: Removing the growing tips from broad beans will deter aphids