Tufted vetch (Viccia cracca) is a weedy perennial legume that is difficult to manage in cropping systems that use reduced tillage and particularly when annual legume crops like soybeans are grown.
Tufted vetch also exhibits high tolerance to many herbicides, most notably glyphosate. A rate response study was conducted by the University of Guelph over a decade ago and it took three times the normal rate of glyphosate to provide over 80 per cent visual control. Observations made by growers and agronomists are consistent with the public research. Glyphosate applied at rates typically used for pre-plant burn-down applications in soybean do not control tufted vetch.
- More Country Guide: Tufted vetch takes off
If tufted vetch is not adequately controlled before planting, there aren’t any effective herbicides at managing it once the soybeans have been planted. A summary of the most effective herbicide programs used in non-GMO soybeans over three years is shown in Table 2 (below image).
Cause for optimism in 2014 research trials?
This spring, I was able to evaluate a number of pre-plant burn-down treatments that targeted some perennial weeds, including tufted vetch. There were a couple of very impressive treatments, specifically when either flumioxazin (found in Valtera, Step-Up, Fierce and Guardian Plus) or saflufenacil (found in Eragon, Integrity and Optill) were mixed with glyphosate and the adjuvant Merge. I will provide an update in the next issue of Pest Patrol to see if this level of control continues, but for the purposes of providing a quick and clean seedbed for soybean emergence, these treatments have been impressive.
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An important point: I’m choosing to show you the results of one trial with optimistic results so far. I’m doing so because this is a species that more growers struggle with and there aren’t currently many options. It is important to keep in mind that for a weed to be listed as controlled on a herbicide label, a minimum of 10 replicated trials conducted over two growing seasons must be provided. This provides a level of assurance that the herbicide will perform on the labelled species. One trial may be a fluke; we won’t know until this is replicated several times. Therefore expectations for control of tufted vetch with these treatments at this point should be low.
