This project is funded in part by the ASCFG Research Foundation

Effect of pesticide mixtures on the western flower thrips (Frankliniella occidentalis)
associated with cut flowers


A pesticide mixture is a combination of two or more pesticides in a single solution applied simultaneously. Pro-ducers apply pesticides as mixtures to reduce labor costs because fewer applications are required. In addition, pesticide mixtures may expand the spectrum of arthropod (insect and mite) pest activity; thus mitigating populations of multiple arthropod pests encountered simultaneously. Furthermore, there is the possibility of synergism occurring between pesticides used in mixtures. Synergism refers to the toxicity of the pesticides used in the mixture being greater to the target pest when combined, compared to if the compounds were applied separately. However, problems may occur when mixing pesticides including antagonism in which the level of efficacy (based on mortality) is reduced when pesticides are combined.

Cut flower producers, in either field or greenhouse environments, commonly mix together various pesticides including insecticides and miticides into a single spray solution. This expands the activity of an application thus making it possible to manage the multitude of arthropod pests encountered during the production of cut flowers. However, producers may be inadvertently applying pesticide mixtures that are less effective compared to making separate applications of pesticides or producers are using pesticide mixtures that are harmful to crops (=phytotoxic) resulting in plant injury and economic losses. Furthermore, producers may mix together pesticides with similar modes of action, which may potentially lead to arthropod pest populations developing resistance to the individual pesticides in the mixture. As such, more information is needed to assess the pesticide mixtures that are effective against one of the major insect pests of cut flowers, the western flower thrips, Frankliniella occidentalis. Therefore, the objective of this research was to determine pesticide mixtures that are effective in controlling populations of the western flower thrips on cut flowers under greenhouse conditions.

Materials and Methods

There were a total of three experiments designed to evaluate specific pesticide mixtures and determine those which demonstrated efficacy against the western flower thrips. All experiments were conducted in a glass-covered greenhouse, and the procedures were similar for the three experiments. Yellow cut transvaal daisy, Gerbera jamesonii flowers were used in all three experiments. Each cut flower was artificially infested with approximately 15 to 20 adult western flower thrips. All flowers were sprayed with the appropriate treatments using a 1-quart plastic spray bottle two days after post-infestation.

The three experiments were conducted with different treatment combinations (mix-tures), and there were five replications per treatment and treatment combination. The treatments and combinations, and rates used for each experiment are presented in Table 1.
Results and Discussion

For experiment one, all the spinosad (Conserve) and abamectin (Avid) treatments and combinations provided sufficient mortality (≥90%) of western flower thrips whereas the other treatments were less effective against western flower thrips with mortality ≤50% (Figure 1). The treatments and treatment combinations associated with experiment two that were effective against western flower thrips were abamectin + bifenazate (Sirocco), abamectin (Avid), abamectin (Avid) + bifenazate (Floramite), pyridalyl (Overture), and pyridalyl (Overture) + petroleum oil (Pure-Spray Green) with mortality ≥80% (Figure 2). For experiment three, both spinosad (Conserve) and pyridalyl (Overture), and all of the treatment combinations including those containing the fungicides fenhexamid (Decree) and azoxystrobin (Heritage) provided sufficient morality (≥80%) of western flower thrips (Figure 3). Overall, all the pesticide mixtures evaluated were effective in controlling western flower thrips in cut transvaal daisy flowers with no evidence of antagonism.

This study has shown that most of the mixtures evaluated in the experiments were not antagonistic in regards to inhibiting mortality of western flower thrips populations. Therefore, our data indicates that these pesticide mixtures may be used by cut flower producers without compromising effectiveness against populations of the western flower thrips.

For more information, or to see the tables associated with this report, contact Raymond at [email protected]


I thank the Association of Specialty Cut Flower Growers Research Foundation for providing funding for this research. I also acknowledge the technical support of Amy L. Willmott (Kansas State University; Manhattan, KS).

Raymond Cloyd


Raymond Cloyd is Professor and Extension Specialist in Horticultural Entomology at Kansas State University. For more information, contact him at [email protected]