Keeping thrips uder control in late March and April

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Late March and April is the time that populations of thrips in greenhouses really start to explode. A combination of three factors is responsible for this. First, warmer temperatures and longer days give overwintering thrips the green light to reproduce. Second, an ample supply of pollen and warmer temperatures allow thrips to reproduce faster. Finally and most important, the low number of thrips present in greenhouse crops since February have now completed a second generation, turning 100 thrips into 30,000 thrips. This always comes as an unwelcome surprise in late April. The best way to avoid problems with thrips is to watch the scouting reports carefully and begin your thrips management program when thrips numbers begin to increase on yellow sticky cards.

Thrips management

When the number of thrips per yellow sticky card increases beyond your tolerance level (for most growers the threshold is from 10 to 100 per card), spray the infested greenhouse sections with one of the following products every five days for four applications. Conventional sprayers usually give better results than foggers. Obtaining good coverage of stems and the undersides of leaves improves control. High spray pressure and good air movement usually result in the best coverage.

Choose from the following list of products for thrips control. Using a product from a different chemical class every six weeks may help slow the development of thrips resistance. However, mixing different products together, or spraying different products in the same month will not slow the development of resistance. Chemical classes are shown in parentheses after each product name. For a description of the chemical classes see the new wall chart ‘Insect Controls for the Greenhouse Industry, MSU Extension Bulletin E-2696.

Avid (6), Mesurol (1), Orthene 97 (1), Pedestal (15), Pylon (13), Safari (4a) Sanmite (21), Tristar (4a), and Conserve (5).

Note: some thrips populations may be resistant to Conserve.

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