Such deformities are easily seen if the leaf is examined with the light source behind it. Severely affected plants can be so deformed as to be unmarketable, and head lettuce varieties may fail to form a head. However, infected plants showing less severe symptoms can still be harvested. The big vein agent in California has yet to be identified, although researchers are fairly certain that it is a virus, possibly tobacco stunt virus. Even though the agent is soilborne and therefore always present in infested fields, disease severity may vary greatly from season to season.
Big vein is more prevalent and severe during cool weather.
In fields having chronic and severe big vein histories, avoid planting susceptible cultivars during spring. Some big vein resistant cultivars are now available. Crop rotations are not effective in controlling big vein. The Regents of the University of California. All rights reserved.