Laboratory and field experiments were conducted to monitor the development of pesticide resistance in populations of Eotetranychus hicoriae (McGregor) from Louisiana. Results of these studies indicated that pecan leaf scorch mite (PLSM) populations from 3 orchards near Monroe, LA. have developed resistance to the broad spectrum organophosphate pesticides currently registered for use on pecans.

In laboratory dosage-mortality experiments, the Monroe populations were 61.8 to 71.8x more resistant to phosalone, 4.2 to 5.8x more resistant to dialifor, and 8.1 to 13.9x more resistant to dimethoate than a population from Shreveport which served as the baseline culture. The Monroe populations gave similar responses as the Shreveport population to the acaricides, dicofol, propargite, cyhexatin, and fenbutatin-oxide. In field trials at Monroe, phosalone and dimethoate failed to control PLSM while propargite, cyhexatin, and fenbutatin-oxide provided adequate control.

The confirmation of pesticide resistance in PLSM is the first documentation of resistance in a pecan arthropod pest. The consequences of this resistance to the direction of pecan pest management are discussed.