Generally, no serious insect attack has been observed on this crop. In rare cases the crop may be attacked by the capsule borer (Heliothis spp.), which can cause considerable loss in yield. But the pest can easily be controlled by spraying with the insecticide Pay-off (100 EC) at the rate of 625 ml/ha in 500 I of water. The two main diseases of linseed are wilt (Fusarium oxysporum) and powdery mildew (Oidium lini Skoric). Wilt infection occurs in the early stages of plant growth and may continue until the capsules are formed. If the seedlings are infected, further growth of the plant ceases and the infect- ed seedlings die. The disease causes the leaves to shrivel and the plants to droop and ultimately die. The fungus may persist in the soil for several years even if linseed is not grown. It may also be seed-borne.
The best way to avoid the disease is to grow resistant varieties. To get rid of seed infection, treat seed with Vitavex or Derosol at 2.5 g/kg of seed. Crop rotations may also help to reduce the incidence of the disease. Powdery mildew assumes greater importance in irrigated crops. The attack occurs at the flowering stage. White powdery spots form on the leaves, spreading quickly to cover the entire plant. Heavy incidence of the disease adversely affects seed formation and development. Treatment of seed with Vitavex or Derosol at 2.5 g/kg of seed may control the disease.