In California, a threshold of 30 thrips per plant at mid-season has been used successfully for dry bulb fresh market and drying onions, using conventional, synthetic pesticides. This number would be adjusted downward for very young plants, and upward for larger mature plants. When considering appropriate action threshold levels, it is important to remember that no single number will always be reliable as a guide. Climate is a factor. Hot and dry conditions favor thrips damage and cool rainy weather hinders it.
Plant architecture can also influence thrips population levels.
The choice of cover crops can affect the number of overwintering thrips. Wheat and rye provide excellent overwintering sites for thrips and should be avoided. Weed destruction in the field and surrounding margins can also help to reduce thrips populations, since these areas serve as overwintering and re-infestation sites. Thrips are color-sensitive, suggesting that colored mulches may be effective in their control. To make the mulch, black plastic was spray-painted in the field with aluminum paint.