Control of the recently-introduced weed butterprint (Abutilon theophrasti) in maize

Butterprint (velvetleaf in many countries) is one of the worst broadleaf weeds in maize (Zea mays) and soya bean (Glycine max) crops in USA. It has been accidently introduced into New Zealand on several occasions. Recently it has been found in three maize fields in Waikato and has become well established at one 20 ha site. Twelve different post-emergence herbicides were evaluated for control of butterprint in glasshouse pot trials and in a field trial. In the glasshouse bromoxynil, dicamba, mesotrione, aminopyralid and topramezone all gave 100% control. In the field trial, dicamba showed the most activity but overall efficacy was less than in the glasshouse. Dicamba controlled most of the plants that were present at spraying, but germination over the next month resulted in a final population of 88% of the original. This population of butterprint also shows a very high tolerance to atrazine when treated post-emergence.