Western flower thrips (Frankliniella occidentalis) are difficult to control. Their secluded behavior protects them from many insecticides; eggs are inserted into plant tissue, the larvae feed in tight, protected areas, such as flower buds or growth terminals, the pupal stages occur in the soil-media, and the adults feed within protected areas. Thrips may eventually come into contact with insecticides when the right spray equipment and application interval are used. However, chemical control may not be effective when there is insecticide resistance in the population. In response to high levels of resistance recently found in vegetable fields in Florida, Dow AgroSciences has suspended the sale and use of products containing spinosad in Broward County and a portion of Palm Beach County, FL.
This drastic and unprecedented action taken by Dow AgroSciences in Florida is yet another ‘red flag’ indicating the importance and possible consequences of insecticide resistance. We should all view this as an opportunity to take a closer look at our pest control toolbox and make sure it includes sound insecticide resistance management practices, to avoid similar problems in Texas. The good new is that so far, most Texas growers have thrips populations that are still susceptible to spinosad (Conserve®). Earlier this year, I monitored western flower thrips for their tolerance to spinosad. Most of the greenhouse locations sampled did not have large thrips populations. Since these growers primarily use Conserve®, the low populations suggest good efficacy in most cases. However, I did detect very high tolerance levels (immunity) to Conserve at one Texas location. Since then this particular grower has agreed to completely stop using Conserve for at least 6 months.
The most important thing we can do to avoid pesticide resistance is to properly rotate pesticides based on their mode of action. Rotation is essential for all pesticides groups: herbicides, fungicides, bactericides and insecticides. The first evidence of resistance is usually reduced efficacy against the target pest even when the pesticide was properly applied at the recommended rate. If you suspect a pest population is developing tolerance to a particular chemical, continued use or increasing the rate of the product will only accelerate the rate of resistance selection, eventually leading to complete control failure.
To avoid resistance to spinosad, do not make more than two consecutive applications of Conserve®. If additional treatments are needed, rotate with products with different mode of action for at least two subsequent applications. There are a number of effective products available for thrips control. The list includes (but is not limited to) those products containing abamectin, Beauveria bassiana, chlorfenapyr, chlorpyrifos, dimethoate, fenoxycarb, methiocarb, novaluron, pyridalyl and tau-fluvalinate.
If you suspect insecticide resistance or need further information, please do not hesitate to contact me.
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