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Thursday, January 8, 2009

Alfalfa Mosaic Virus

Alfalfa Mosaic Virus

Aphid-Transmitted Bacilliform Virus
Found : worldwide World Vegetable Center


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 as quickly, but the aphid actually retains the virus for
only a short period of time. The virus is also readily
transmitted mechanically and by grafting.
Conditions for Disease Development

Alfalfa mosaic virus (AMV) is found most commonly in
pepper crops that have been planted near alfalfa, clover
or other legumes. It is generally considered to be a
minor threat to pepper production.
Transmission by seed is the primary means of
establishment of the virus while aphid transmission is
more important for the subsequent spread in field
plantings. AMV is transmitted by many species of
aphids including the green peach aphid, Myzus
persicae. The aphid can acquire the virus by feeding on
an infected plant for less than a minute and can transmit

Pepper varieties resistant to AMV are not available.
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 (alfalfa, pepper, tomato, tobacco, potato,
clover, many cucurbits and beans, and several other
crops and weeds) and numerous aphid vectors.
Use virus-free pepper 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.
AMV-infected vegetable seedlings are potential
primary sources of the virus. Cover seedlings with mesh
size of 32 or higher to prevent aphids. Do not clip or
damage young seedlings since this increases the possibility
of mechanical transmission of the virus from
contaminated tools or hands.
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.
Disinfect tools, stakes, and equipment before moving
from diseased areas to healthy areas. Work in diseased
areas last, after working in unaffected parts of a field.
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 pepper crop with mineral oil to delay
virus spread in the field by interfering with aphid
transmission of the virus.

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