Onion - Plant management

Friends,

The website : https://plantvillage.psu.edu/topics/onion/infos has many good article on Onion plant management.

Often we get questions on pests damaging the Onion plants. Here are some details on how to control each of them, other than the various fungus.

Category : Mites

Bulb mites Rhizoglyphus spp.
Tyrophagus spp.

Symptoms

Stunted plant growth; reduced stand; bulbs rotting in ground or in storage; pest is a cream-white, bulbous mite <1 mm in length, which resembles a pearl with legs

Cause

Arachnid

Comments

Damage to plants by bulb mites allows secondary invasion by other pathogens and can cause bulb rots

Management

Do not plant successive crops of onion or garlic in same location; allow field to fallow to ensure that any residual organic matter decomposes completely - crop residues can harbor mite populations; treating garlic seed cloves with hot water prior to planting may help reduce mite populations

Category : Insects

Leafminers Lyriomyza spp.

Leafminer trail on onion leaf

 

Leafminer damage to onion foliage

 

Symptoms

Thin, white, winding trails on leaves; heavy mining can result in white blotches on leaves and leaves dropping from the plant prematurely; early infestation can cause yield to be reduced; adult leafminer is a small black and yellow fly which lays its eggs in the leaf; larave hatch and feed on leaf interior

Cause

Insects

Comments

Mature larvae drop from leaves into soil to pupate; entire lifecycle can take as little as 2 weeks in warm weather; insect may go through 7 to 10 generations per year

Management

Check transplants for signs of leafminer damage prior to planting; remove plants from soil immediately after harvest; only use insecticides when leafminer damage has been identified as unnecessary spraying will also reduce populations of their natural enemies

Onion maggot Delia antiqua

Onion maggot and bulb damage

 

 

Symptoms

Stunted or wilting seedlings; plant will commonly break at soil line if an attempt is made to pull it up; if infestation occurs when plants are bulbing, bulbs will be deformed and susceptible to storage rots after harvest; adult insect is a greyish fly which lays white, elongate eggs around the base of the plant; the larvae that emerge from the eggs are tiny and white and bore into the onion plant; mature larvae are about 1 cm (0.4 in) long with feeding hooks

Cause

Insect

Comments

Females can lay several hundred eggs during their 2-4 week lifespan; insect overwinters as pupae in the soil

Management

Management of onion maggots is heavily reliant on good sanitation; all onion bulbs should be removed at the end of the season as maggots will die without a food source; commercial onion growers must often rely on the application of appropriate granular insecticides and, in some cases, insecticide sprays are also required; home gardeners should try to remove any volunteer wild onion and chive plants as these can act as an infection source; floating row covers may provide protection by preventing females from laying eggs around the plants

Thrips (Onion thrips, Western flower thrips) Thrips tabaci
Frankliniella occidentalis

Onion thrips nymphs feeding on onion leaves

 

 

Symptoms

Discolored, distorted tissue; scarring of leaves; severly infected plants may have a silvery appearance

Cause

Insect

Comments

Thrips are most damaging when they feed on onions at the early bulbing stage of development; both onion thrips and western flower thrips have an extensive host range and can be introduced to onion from other plants

Management

Natural enemies include some species of predatory mite, pirate bugs and lacewings; avoid planting onion in close proximity to grain fields as thrips populations build up on these plant in the spring; overhead irrigation of plants may help reduce thrips numbers; apply appropriate insecticides at first sign of thrips damage