Alfalfa mosaic virus

Alfalfa mosaic virus is a worldwide distributed phytopathogen that can lead to necrosis and yellow mosaics on a large variety of plant species, including commercially important crops. Transmission of the virus occurs mainly by some aphids, by seeds or by pollen to the seed. It also has a wide host range (alfalfa, pepper, tomato, tobacco, potato, clover, many cucurbits and beans, and several other crops and weeds).

Symptoms
The foliage has a distinct bright yellow to white mosaic that sometimes causes large areas of interveinal leaf tissue to be bleached in appearance. Chlorotic line patterns and veinal necrosis also may occur. Generally, the leaves are not distorted in shape. If infected when young, the plants may be stunted and their fruit will be misshapen.

Control
Various control measures are required because AMV is transmitted by seed, aphids, and mechanically. Control measures must take into account the disease’s wide host range and numerous aphid vectors.

Use virus-free seed. Check transplants for any symptom development and discard those with symptoms. One or two transplants on either side of the affected plants should also be discarded. Avoid touching or handling healthy plants after handling plants suspected of virus infection. Wash hands with soap afterwards or use disposable gloves when handling infected plants.

Aphid control may be difficult because the virus is transmitted very rapidly by these insects. Use fastacting insecticide sprays since aphids may move to other nearby unsprayed plants when disturbed.

Other less effective measures include: planting barrier crops that are not susceptible to AMV such as corn, applying sticky traps, or covering the ground with an aphid deterrent material like aluminum foil strips. Another control strategy is to grow trap crops nearby that attract aphids and then spray these plants with a contact insecticide to destroy the aphid populations. Also, spray the crop with mineral oil to delay virus spread in the field by interfering with aphid transmission of the virus.