In a 2014 column, I expressed my optimism for a herbicide treatment to control vetch (Viccia cracca) before planting soybeans. I wrote, “2,4-D Ester 700 applied seven days prior to soybean planting looks like a promising tool for the control of vetch in soybeans provided vetch has emerged at the time of application. More trial work will be needed to verify the consistency of these results.”
After a completing a second season of evaluations in 2015, I have not swayed from that optimism, although it is tempered since the level of control in 2015 was not nearly as good as in 2014. Still, it was significantly better than all other treatments.
Why the difference in control?
Vetch appears to be a later-emerging species. Since the spring of 2014 was relatively wet, soybeans were not planted until the first week of June when there was a higher percentage of emerged vetch. In 2015, by contrast, the spring was relatively dry and soybeans were planted some three weeks earlier than in 2014, which meant less vetch was emerged at the time of pre-plant applications.
An average soybean yield loss of 35 per cent has been observed over two seasons due to vetch interference. 2,4-D Ester has been the most effective active ingredient on vetch, but its effectiveness has depended on the amount of vetch that is emerged at time of applications.
Have a question you want answered? Hashtag #PestPatrol on Twitter to @cowbrough or email Mike at firstname.lastname@example.org.