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Bulletin

Article Title

Onion Thrips in Iowa

Abstract

1. Onion thrips have long- been an established pest in Iowa and in certain years cause severe loss to the onion crop of this state.

2. Young and adults produce the “ white blast” of onions by sucking the juices from the leaves.

3. Hot, dry weather in July and August is favorable to the rapid multiplication and subsequent spread of the onion thrips.

4. The onion thrips spreads from infested fields to those uninfested, chiefly in the winged adult stage, by drifting in the air with the wind.

5. There are four principal sources of infestation in the spring, namely: set or multiplier onions, greenhouses where tomatoes or cucurbits are grown, piles of refuse such as tops, culls and screenings which are left in the field over winter, and wild perennial host plants.

6. These sources of infestation can be very largely eliminated, with the result that thrips epidemics can be at least greatly reduced.

7. Results of three seasons’ spraying tests with nicotine sulfate and soap for the control of the onion thrips, has demonstrated that under Iowa conditions this is not effective in seasons when these insects are abundant enough to cause damage. This is largely because this insecticide does not kill the eggs within the leaf, nor the pupae in the soil at the base of the plants, and also because many larvae escape by being in the axils of the leaves. Furthermore, many winged adults escape and later rein fest the sprayed plants.

8. Where comparatively few plants are infested early in the season, the thrips breeding on them can be controlled to advantage by spraying with nicotine sulfate and soap to prevent later infestation of larger areas. Control is effective at this time because the plants are small and practically all the insects can be hit by the spray.

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