Big Vein (virus): Infection may appear at any stage of growth. Very young seedlings are killed. Surviving plants are smaller in size, the quality of heads is affected and maturity is delayed. Infected leaves have an upright habit of growth. Areas around the veins clear, causing the veins to appear enlarged. The virus is transmitted by Olpidium brassicae, a soilborne fungus found in the fine roots of many plants. The virus may persist in the fungus in soil for up to eight years. Avoiding excessive soil moisture and rotation are the means of reducing disease losses. Varieties may differ in tolerance.
