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Efficacy trials of OMRI approved materials on vegetable crops

Onion thrips

Onion thrips can be serious pests of onions and cabbage in hot, dry seasons. On onions, the thrips rasp away at the surface of leaves, leaving bleached-looking areas with no chlorophyll, which can reduce photosynthetic capacity and yield. On susceptible cabbage varieties thrips feeding can cause raised, warty areas to form on the leaf, although this is not a problem I’ve ever heard organic growers having to any serious extent. In fact, this fall I heard about a large field of organic cabbage that did not have high thrips populations during the 2001 growing season when the surrounding conventionally managed fields had serious thrips problems. Tony Shelton is planning to do some research to find out what’s going on in the organic fields that’s not going on in the conventional fields.

The thrips trials were conducted in the greenhouse on 5-6 leaf onion plants (variety Stuttgart) grown from sets. Plants were treated, and field-collected immature thrips were caged on individual plants for five days, after which time surviving thrips were counted.


Treatment Rate/A % Mortality


0.3 qt.

69 a

Engelhard F-01-KV-3

15 lb.

61 ab

Engelhard F-01-KV-6

15 lb.

58 ab

Surround WP

15 lb.

64 ab

Neemix 4.5

1 pt.

48 ab


8 oz.

46 ab

Rotenone 5%

48 oz.

39 b



0 c

* Adjusted to account for the background population of thrips in the greenhouse
Values followed by the same letter are not significantly different

All of the treatments reduced thrips numbers compared with the control. Rotenone caused the lowest mortality, and Mycotrol (a commercial product containing the entomopathogenic fungus Beauveria bassiana) the highest. The three kaolin formulations (Surround WP and the two numbered formulations) and the two neem products (Neemix and Ecozin) produced intermediate mortality levels.