Beans

Pests of Field Crops in Southern Africa

BEANS

(mainly Phaseolus species, Fabaceae)

Text Box: Aphids can sometimes be a problem on beans, although they are probably more serious in temperate climates than in the sub-tropics. The main species of aphids to attack beans are Aphis fabae and Aphis craccivora (see groundnut section for information on the latter). A. fabae is a small (1.5-2 mm), dull black species, sometimes with the segments of the abdomen marked with a powdery secretion. It has a very wide host range, including many legume species and weeds from a variety of families (such as Amaranthus, Conyza, Galinsoga, Datura stramonium and Tribulus terrestris). A variety of systemic and contact insecticides is available for control, should this be necessary. TOP

Text Box: See general section. This pest has usually only been seen as a problem on bean crops which have been sprayed extensively for other pests, thereby destroying their natural enemies. TOP

Text Box: See general section. Mining damage by this fly may be quite conspicuous on lower leaves of beans, but seldom reaches problematic levels, and would be best left to come under natural control. TOP

Text Box: See general section. Thrips can become a problem mainly in fine vegetable bean crops that are destined for export, since their egg-laying can cause tiny raised spots which are unacceptable to a sophisticated market. They may be difficult to control in these circumstances. TOP

Text Box: See general section. Bean crops that coincide with the arrival of the main rains are often subjected to a degree of foliar damage caused by chafer beetles. These small brown beetles feed by making zigzag holes in the leaves during their nocturnal forays into the crop, and although they are quite easily controlled by use of contact insecticides, the damage is usually of a transitory and cosmetic nature, not requiring control. The larval form of chafer beetles, whitegrubs, are sometimes a pest of beans. TOP

Þ

Þ

Þ

Þ Bean Stem Maggot

Þ

Þ

Þ

Þ

Þ Red Spider Mite (see general information)

White tunnels in bean leaves left by Liriomyza larvae.

Aphids on the underside of the leaf.

African Bollworm

Text Box: See general section. In some seasons damage by African bollworm to flowers and pods can be extreme. Neat round holes in the pods with plenty of frass are diagnostic. Control can be difficult once the pest is protected within the pods and should therefore rely on scouting to detect early damage in the flowers. TOP

African Bollworm

Heavy infestation of African bollworm in bean crop.

Whitefly on the underside of the leaf.