|The Winged Bean: High-Protein Crop for the Humid Tropics (BOSTID, 1981, 41 p.)|
When grown in mixed garden cultivation or shifting agriculture, the winged bean is unusually free of pests and diseases. Nevertheless, the plant is known to be susceptible to a number of pests and diseases, and the importance of these may become greater with larger stands of single varieties. There are, however, few detailed studies. Until disease- and insect-resistant varieties are identified, the danger of diseases in winged beans grown in monoculture can be limited by planting more than one variety, as in the more extensive acreage now planted with winged bean in Thailand.
A number of pests and diseases are identified in this appendix as a sort of "distant early warning" for readers. Details can be found in literature cited in Appendix B.
Insect predators vary in importance from one country to another, depending on the climatic and geographic regions.
The bean pod borer Maruca testulalis is the most widespread flower pest in Papua New Guinea and Thailand; it also attacks the stem end of the pods. Lampides boeticus attacks the flowers and pods. Nezara viridula infests the pods but causes no appreciable damage, while Heliothis armigera causes some pod damage in India.
The bean fly Ophiomyia phaseoli is sometimes a serious seedling pest. Larvae bore through the stems and mine the leaves. The black bean aphid Aphis craccivora is commonly found on shoots of young plants in Papua New Guinea, but it causes more severe damage in Guam where 2-20 percent damage may occur. Polyphagotarsonemus latus is another serious pest of shoots in Guam.
A number of pests feed on the leaves. Their effects depend on the climate, natural enemies, and growth stage of the plant. Young plants are attacked by Ophiomyia phaseoli, Aphis craccivora, and Planococcus citri. Under dry conditions spider mite damage by Tetranychus sp. and Polyphagotarsonemus latus can be severe. The ladybird Henosepilachna signatipennis also causes extensive leaf damage through the feeding activities of both adult and larvae.
Chemical-control measures are not normally recommended for subsistence agriculture, although there have been trials with chemical sprays on experimental plots. Screening for insect-resistant lines would be the most promising method for control, especially since a large amount of germ plasm is available.
Virus-like symptoms have been found in winged beans growing in Papua New Guinea, Indonesia, Ghana, Ivory Coast, Trinidad, and the Philippines.* These include Psophocarpus necrotic mosaic virus, Psophocarpus ringspot mosaic virus, and leaf-curl and little-leaf of unknown etiology. Aphis craccivora can transmit Psophocarpus ringspot mosaic virus and therefore has a dual role as pest and vector.
Leaves of plants affected with Psophocarpus necrotic mosaic virus are necrotic and distorted, show an occasional yellow mosaic pattern, and may have reduced leaf surface. Leaves of plants infected with Psophocarpus ringspot mosaic virus have light-green ring spots. Leaves infected with leaf-curl become dark green, thickened, and dwarfed, they curl downwards and show abnormal branching.
Knowledge of virus diseases and their control is still incomplete, but severe damage has occurred in Indonesia, Ivory Coast, and Ghana.
False Rust "False rust" or "orange gall" is caused by the obligate fungal parasite Synchytrium psophocarpi. The symptoms are the appearance of bright-orange pustules along the veins of young leaves and on stems, pods, and sepals of flowers. Infection leads to hyperplasia and galling, with abnormal branching at the nodes. The fungus attacks only Psophocarpus tetragonolobus. Psophocarpus scandens is immune. The disease occurs in Papua New Guinea, Philippines, Indonesia, and Malaysia. It has been suspected but not confirmed in West Africa.
The disease affects pod production and possibly seed yield. All Papua New Guinea varieties are susceptible, but some disease-resistant varieties have been found in Indonesia. The disease is a serious problem during the rainy season, when it can assume epidemic proportions.
Pseudocercospora Leaf Spot Pseudocercospora psophocarpi attacks the leaves; the first symptoms are yellow spots on the upper surface. The under surfaces have a whitish bloom, which becomes grey and finally black as the leaves mature. This is followed by necrosis of the entire leaf. The disease occurs in Papua New Guinea, Philippines, Malaysia, and Indonesia; it is especially destructive during the rainy season. All Papua New Guinea lines are susceptible. Psophocarpus tetragonolobus is the only known host at present. Here, too, Psophocarpus scandens is immune. A similar disease is also caused by Cercospora psophocarpicola in Singapore§ and Cercospora canescens in Bangladesh.
Powdery Mildew The symptoms of powdery mildew are powdery white patches on the leaves.** Only the imperfect Oidium stage of the fungus has been recorded. The disease occurs in the Highlands of Papua New Guinea and in Indonesia, but there is little information on its economic importance.
Collar Rot Collar rot affects seedlings 3-4 weeks old. The symptoms are wilting of the leaves followed by the death of the plant. The hypocotyl region of affected plants is usually constricted, with black necrotic lesions at soil level. This disease caused severe field losses in Papua New Guinea. Macrophomina phaseolina, Fusarium semitectum, F. equiseti, F. moniliforme, and Rhizoctonia solani were the main associated fungi. The disease was influenced by soil type, depth of sowing, and inoculum density. Shallow planting in welldrained soils has been recommended for control.
Root Knot The root-knot nematodes (Meloidogyne incognita and Meloidogyne javanica) can cause severe galling of roots; this not only damages the roots but also reduces tuber production and may affect pod and seed yield. These nematodes are cosmopolitan and have a wide host range. Damage to winged bean has been reported in Papua New Guinea, Philippines, Ivory Coast, Indonesia, and Mauritius, but the problem arises wherever the plant is grown and is especially troublesome in sandy soils. Most of the Papua New Guinea lines are susceptible, and a screening for root-knot resistance of the winged bean world germ plasm collection is needed.
Thanetophorus cucumeris causes a leaf blight in Papua New Guinea, Sarawak, Sabah, and West Malaysia. Mycosphaerella sp. has been associated with a concentric ring spot in Papua New Guinea. Choanephora cacurbitarum is associated with flower blight in Papua New Guinea and Sarawak, and AIyrothecium roridiurm with a leaf spot in Malaysia.
Colletotrichum lindemuthianum occurs in Papua New Guinea and Colletotrichum gleosporides (Glomerella cingulata) in the Ivory Coast.*