Managing thrips infestation in onion

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Managing thrips infestation in onion
Thrips are the most damaging insect pests of onion, causing severe
yield loss. The pests prefer to feed on young plant tissues from newly
emerged leaves. When the leaf grows, the previous damage produced by
the thrips enlarges, leaving empty spaces on the surface of the leaf.
Affected leaves show silvery patches or streaks which shine in the
sun.
In case of severe damage, these patches occupy most of the surface of
the leaves and the plant cannot adequately photosynthesise.

Affected plants
The damaged plants tend to lose more water than normal plants and turn
white or silver in colour and leaves wither. The bush size in the
affected plants becomes reduced.
Thrips incidence predisposes the onion crop to the serious fungal
disease of onion that is purple blotch. The purple blotch incidence is
always higher on thrips infested plants.
Onions, garlic and other related plants are the preferred hosts of
thrips. However, they can attack other crops such as cabbage, cotton,
tomatoes, beans, cucumber and many other cultivated crops.

Management
Thrips are not a problem during monsoon because rains wash the thrips
population from the plant.
Planting time should be selected accordingly and continuous and
staggered planting in a given area should be avoided. Proper crop
rotation should be followed.
Water management is important, as the onion plants under water stress
suffer most from thrips injury.
Adequate proper nutrient management helps to reduce the impact of
thrips in onion. If onion crop is to be transplanted, the seed beds
should be distant from the old plantings and new plots to be planted.

Bio control
Neem preparations are useful especially when the pest population load
is low to moderate.
The success of the chemical control depends on how the chemical is
placed on to the crop.
For better retention of the chemical on the crop it is desirable to
add a sticker (wetting agent) along with pesticide at the rate of 1 ml/
lit of the spray fluid.

G. Gajendran, D. Dinakaran & S. Vijay
Anbil Dharmalingam Agricultural Collegeand Research InstituteTiruchi,
Tamil Nadu