Spider mite resistance to miticides in South Carolina strawberry and implications for improved integrated pest management

Authors: BERGERON, PAUL - Washington State University; Schmidt, Rebecca

Submitted to: Experimental and Applied Acarology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2021
Publication Date: 5/10/2021
Citation: Bergeron, P., Schmidt-Jeffris, R.A. 2021. Spider mite resistance to miticides in South Carolina strawberry and implications for improved integrated pest management. Experimental and Applied Acarology. 84:407-418. https://doi.org/10.1007/s10493-021-00621-7.
DOI: https://doi.org/10.1007/s10493-021-00621-7

Interpretive Summary: Twospotted spider mite is a prominent pest of strawberries in the Southeastern US, and are typically managed using specific pesticides (acaricides). Spider mites are known to rapidly develop pesticide resistance which makes it important that growers have up-to-date information about which acaricides are still successful and to which products spider mites are resistant. In South Carolina, strawberry growers and extension agents have reported field failures of acaricides, but spider mite resistance has not been documented. Because of this, researchers at the USDA-ARS in Wapato, in collaboration with Washington State University, conducted a study to evaluate the effectiveness of acaricides registered for use on strawberry. This study was conducted on 6 different populations of spider mites collected from across South Carolina, and the results of the field-collected populations were compared to a known-susceptible lab colony. From this study, we found out that the populations tested were highly resistant to bifenthrin and fenbutatin-oxide. Bifenthrin is a broad-spectrum pesticide and fenbutatin-oxide is an older acaricide meaning we need to continue reducing the use of broad-spectrum pesticides and older products, in favor of newer acaricide chemistries because of the high levels of resistance. One population was also found to be resistant to abamectin, but no resistance was found to the other products registered for use on strawberry. Overall, this suggests that spider mite resistance in South Carolina strawberry is low and that any reported field failures of other acaricides are potentially related to spray coverage or problems during application

Technical Abstract: Tetranychus urticae Koch, twospotted spider mite (Acari: Tetranychidae), is a major secondary pest of strawberry and can cause significant yield loss. Tetranychus urticae is typically controlled using miticides, which has led to rapid resistance development. In South Carolina (U.S.A.), extension agents and growers have reported field failures of miticides, but resistance has not been rigorously documented. In this study, we determined the level of miticide resistance of T. urticae populations found on strawberry across South Carolina. We examined efficacy of all miticides registered for use on strawberry by conducting an initial diagnostic bioassay at 1/5 the maximum labeled field rate. Any population × active ingredient combination resulting in less than 50% mortality was identified as potentially resistant from the initial bioassay, and concentration-response bioassays were conducted to calculate LC50 values for an individual population. These values were compared with those of a known-susceptible population. Our results indicate that South Carolina populations of T. urticae from strawberry are highly resistant to bifenthrin and fenbutatin-oxide, with one population also exhibiting resistance to abamectin. No resistance was found to hexythiazox, etoxazole, acequinocyl, bifenazate, fenpyroximate, spiromesifen, or cyflumetofen. This suggests that the miticide resistance of T. urticae in South Carolina strawberry is low overall, and that reported field failures are likely due to issues related to spray coverage or application error. Overall, this work supports the need to reduce the use of broad-spectrum pesticides and older products, in favor of newer miticide chemistries due to resistance issues