Thrips on Fall Lettuce (October 29, 2014)

The weather this fall is as warm and humid as I can ever remember. These conditions are no doubt one of the main reasons insect pressure continues to be heavy on our local produce crops as we approach November. Thrips and their associated scarring damage on leaves are beginning to show up on leafy vegetables throughout the desert. Their presence on these crops is not unusual in the fall and will likely remain steady until the weather breaks or we get a good winter rain. We have observed predominantly two species on lettuce this fall; the typical western flower thrips, Frankliniella occidentalis, and the bean thrips, Caliothrips fasciatus. Both are common in the fall, but bean thrips are the predominant species we’re currently seeing on lettuce at the Yuma Ag Center. It’s has also been causing significant damage to small organic lettuce in the Imperial Valley (see image below). Adult bean thrips are uniformly dark, almost black in color and their wings have two black and two white bands which can easily be distinguished with a 10-15X hand lens. Alfalfa, melons, cotton, lettuce and a number of grasses are all known host crops for the bean thrips. The good news is based on my research experience, they can easily be controlled with available insecticides such as Radiant, Lannate (methomyl), acepahate and Entrust/Success. Note: the key to preventing thrips from significantly scarring leafy vegetable plants is to prevent the larval populations from becoming established. With the temperatures we’re currently experiencing, western flower thrips larvae can complete development in about 7 days. Applying back-to-back spray applications ~ 5 days apart is an effective approach for controlling nymph populations once they become established. For more information on the identification, biology, ecology and management of thrips on desert produce please visit these links:

1. Insect Management: Western Flower Thrips
2. Thrips Management in Desert Leafy Vegetables

Remember, When in Doubt . . . . . “SCOUT”