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.
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.
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.
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