Symptoms and Signs
Big vein disease causes the veins in leaves to become very enlarged and clear. Such deformities are easily seen if the leaf is examined with the light source behind it. The enlarged veins cause the rest of the leaf to be ruffled and malformed. Severely affected plants can be so deformed that they are unmarketable. Head lettuce varieties may even fail to form a head. However, infected plants showing less severe symptoms can still be harvested.
Comments on the Disease
The virus that causes big vein is soilborne and is introduced into lettuce plants by a soil fungus (Olpidium brassicae) that attaches itself to lettuce roots. Even though the virus 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 spring 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. No other control options are suggested.
Organically Acceptable Methods
Use cultural controls in an organically certified crop.