What is your plan to control thrips in your greenhouse for 2012?

Whether you are using insecticides or beneficials, early planning is the key to a successful integrated pest management (IPM) program for your greenhouse.

The insect pest that was the topic of contention at the 2011 Great Lakes Greenhouse Expo was western flower thrips, Frankliniella occidentalis. Four different presenters shared their knowledge based on past research, current research and growers input about this pesky pest. Over the last several years, the concern for thrips control has been increasing. Growers complained that they are just not getting the control that they are used to. The concern is that perhaps the thrips have developed resistant to Spinosad, the active ingredient in Conserve SC.

When Spinosad came on the market for use in greenhouses, there was a sigh of relief from the industry. However, the hope that this product would be our answer to western flower thrips for eternity was just that – a hope. The product label has specific resistance avoidance recommendations for proper use to reduce potential for thrips developing resistance. The label states, “Avoidance of the same active ingredient or mode of action consecutive generations of insects or mites. Multiple applications to reduce a single generation are acceptable. If uncertainty of the generation cycle, no more than three consecutive applications should be used, nor should there be continuous use for more than 30 days.”

Most growers I work with could not determine the generation cycles, so they stuck to the no more than three consecutive applications. Growers asked, “Why doesn’t it work anymore, especially if we followed the label?” The theory is problems are due to the movement of young plants globally, and the lack of tracking pesticide treatments. When a greenhouse receives plants from a propagator, the receiver doesn’t know if Spinosad has been applied to those plants or how many applications. If the receiving greenhouse treats thrips by applying Spinosad, then the probability of resistance is accelerated.

As I see it, there are three choices for thrips control: chemical, biological and exclusion. Exclusion is an option that I don’t believe is relevant for Michigan spring plant production since thrips are not entering the greenhouse from the outside. Another option is the use of insecticides. Michigan State University entomologist Dave Smitley has developed information on his top recommendations for products found to be successful in his trials. (See his factsheet on Greenhouse Insect Management.)

Raymond Cloyd from Kansas State University shared with us at the Expo that if you are looking at using “soft” insecticides, a tank-mix of Azitin XL and BotaniGuard ES, Beauveria bassiana, work well together early in your cropping cycle. He indicated that at his trials, BotaniGuard ES alone did not show the results most growers required. We know that thrips rate of development can be as short as 7 to 10 days at optimum temperatures. During the life cycle change and development, the insects are molting (shedding their outer cuticle) so rapidly that the Beauveria bassiana may not get a chance to effectively penetrate the cuticle of the thrips. However, using the two products together, Azitin’s mode of action interferes with the insects molting ability. With the molting process reduced, this allows for the fungus Beauveria bassiana to enter the cuticle of the thrips and, in turn, reduces the pest population.

No matter what you decide for your control tactics, early planning about what products you are planning to use to combat pest outbreaks is key to an effective IPM program.

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