Common onion diseases and pests, symptoms and control(Onions))

Downy mildew

Pale spots or elongated patches on leaves; gray-purple fuzzy growth on leaf surface; leaves turning pale then yellow; leaf tips collapsing

Photo. Symptoms of downy mildew on onion (Kevin et al., 2012)

Management:

• Avoid planting infected sets;
• Rotate crops to non-Allium species for 1-2 seasons,
• Plant in well-draining areas and do not overcrowd plants;
• Destroy all infected crop debris;
• Apply appropriate foliar fungicides taking care to apply thoroughly to waxy leaves.

• Purple blotch (Alternaria porri)

This is the most serious disease of onion, particularly when grown for seed purpose. It also attacks garlic. Disease appears during periods of persistent rain. Infestation of trips also pre-disposes plants to the disease.

Initial symptoms appear as small water-soaked lesions on leaf and seed stalk which later turns brown. As the spot enlarges, purplish zonations with purplish or red margins surrounded by yellow halo will be conspicuous. Under moist conditions, the spot is covered with brown to black spores. Affected leaves and seed stalks fall down and seeds become shrivelled.

Photo. Symptoms of purple blotch on onion

Management:

Spray Dithane M-45, Victory, etc.( 50g/20L of water/2are)

• Stemphylium blight

This is also a serious fungal disease of both onion and garlic. Symptoms appear as small yellow to orange spots or streaks on middle of leaves and flower stalks on one side.

Photo. Symptoms of Stemphylium blight on onion (Kevin et al., 2012)

Management:

Spray Victory 72WP ( 50g/20L of water/2are)

• Rust

Photo: Rust on onion

• Trips (Thrips tabaci)

Thrips are major pests of onion and garlic. Adults are one mm long and yellow brown with dark transverse bands across thorax and abdomen. Both nymphs and adults rasp epidermis of tender leaves and imbibe the oozing sap. Due to rasping of sap, numerous white specks develop. Heavily infested leaves curl up, distort and finally wither away resulting in silver top. This is more serious at flowering stage of seed crop.

Management:

Cultural practices like periodical irrigation and hoeing would reduce infestation to some extent. In severe cases, spray cypermethrin (1cc/1L of water) at 15 days interval