Herbicide Response and Morphology of Interspecific Sowthistle Crosses

Abstract

Interspecific crosses were made between perennial sowthistle (Sonchus arvensisL.) and annual sowthistle (Sonchus oleraceusL.). Flower head size, leaf type, and creeping root growth of the hybrid were intermediate to those same morphological characteristics of the parents. Backcrosses to the parents produced plants which resembled annual or perennial sowthistle more closely than did the F1hybrids. Annual sowthistle and backcrosses to annual sowthistle were more tolerant to (2,4-dichlorophenoxy)acetic acid (2,4-D) and 3,6-dichloro-o-anisic acid (dicamba) than were perennial sowthistle or backcrosses to perennial sowthistle. However, annual and perennial sowthistle were similar to each other in response to 4-amino-3,5,6-trichloropicolinic acid (picloram). Natural crosses between annual and perennial sowthistles may account for some of the variability in herbicide response found in perennial sowthistle.