Comparison of multiple post-emergence Callisto applications for spreading dogbane (Apocynum androsaemifolium L.) control in wild blueberry fields

Spreading dogbane (Apocynum androsaemifolium L.) is a major weed pest in wild blueberry (Vaccinium angustifolium Ait.) fields and is difficult to control. In a 2016 trial conducted in a prune year wild blueberry field, spreading dogbane was sprayed post-emergence with mesotrione (Callisto) at 146 mL/ha or 219 mL/ha product per application to 1 x 4 m split plots, with one half also receiving pre-emergence hexazinone (Velpar). Dogbane emergence and growth were monitored, and plots were sprayed when dogbane reached the 3-5 leaf stage and again after regrowth for a total of three Callisto applications for each rate. Although both Callisto-Velpar combinations (93% control in July) and Callisto 219 mL/ha alone (98% control in July) almost eliminated dogbane, and no new seedlings were observed at the fourth evaluation in July, dogbane was not completely controlled by any treatment. Some of the dogbane stems which appeared dead at the third evaluation in June showed regrowth of lateral leaves in July. T-tests comparing Velpar vs no Velpar indicated that the addition of Velpar slightly increased dogbane control and injury, but the effects were not significant at α=0.05. The commercial landowner’s adjacent treatment of a split Callisto application followed by a mid-summer glyphosate wiper application exhibited better long-term control of dogbane, and warrants further investigation.