Urd Bean Leaf Crinkle Virus
The third trifoliate leafs of seedlings that developed from infected seeds are much larger than usual. These leaves are of lighter green color than usual. Petioles might be shorter and leaf veins thicker, with a characteristic reddish discoloration. One month after planting, leaves start to shrink and crinkle, and become rough and leathery. Plants infected through insect vectors during later growth stages usually develop symptoms in younger leaves, the older ones remaining symptom-free. Leaves show conspicuous venial chlorosis, and the flowers are deformed. Smaller flower buds and stunted growth can be observed. In the few productive flowers, discolored and oversized seeds are visible. Pollen fertility and pod formation is severely compromised, resulting in heavy yield losses.
The virus is often seed-borne, leading to the appearance of a primary infection in seedlings. Secondary infection from plant to plant happens through insect vectors that feed on plant sap such as some species of aphids (for example, Aphis craccivora and A. gossypii), a whitefly (Bemisia tabacci) and a leaf feeding beetle (Henosepilachna dodecastigma). The virus transmission extent and the severity of the disease are determined by the plants degree of tolerance, the presence of vectors in the fields and the prevailing climatic conditions. The virus can decrease grain yield from 35 to 81%, depending on the time of infection.
Different biological means can help to control the infection. Soil or foliar spray application of Pseudomonas fluorescens strains can help to control vector populations. It has been found that fresh butter milk and casein have an effect on the transmission of the disease. Several plant extracts of Mirabilis jalapa, catharanthns roseus, Datura metal, Bougainvillea spectabilis, Boerhaavia diffusa and Azadirachta indica had an effect on the incidence of the virus in the field.
Always consider an integrated approach with preventive measures and biological treatments if available. No chemical treatment against the virus is available but systemic insecticides can be employed to control vector populations. Products containing imidacloprid, allethrin, permethrin, carbaryl or phenothrin can be used as foliar spray applications. Products based on acephate or dimethoatecan may also work. The compound 2,4-dixohexahydro 1,3,5-triazine (DHT) hinders the transmission of the virus and increases its incubation period.