CROSS-RESISTANCE OF A LARGE CRABGRASS (DIGITARIA-SANGUINALIS) ACCESSION TO ARYLOXYPHENOXYPROPIONATE AND CYCLOHEXANEDIONE HERBICIDES

A large crabgrass population (PW2) that demonstrated resistance to flu azifop-P and sethoxydim was identified in Wisconsin during 1992. Dose- response experiments were conducted in the greenhouse to determine the level of resistance of a PW2 large crabgrass accession to aryloxyphen oxypropionate (APP), cyclohexanedione (CHD), and other herbicide chemi stries relative to a large crabgrass accession (A310) which was suscep tible to APP and CHD herbicides. Based on shoot dry biomass reduction, the PW2 accession was 337- and 59-fold resistant to sethoxydim and fl uazifop-P, respectively, relative to the A310 accession. Resistance of the PW2 accession to fenoxaprop, haloxyfop, quizalofop, and diclofop ranged from 18- to 29-fold. The PW2 accession was only 7-fold resistan t to clethodim. Both large crabgrass accessions were susceptible to im azethapyr and linuron. These results suggest that APP and CHD herbicid es will be ineffective for the management of the PW2 accession. An int egrated approach including cultural, mechanical, and alternative chemi cal methods, should be implemented for the management of the PW2 acces sion and to prevent additional resistance problems.