Move over Buckwheat…….
December 21, 2015
Field research often yields observations and findings which are far outside the objectives of the study. Such was the case in 2015 with the Institutes work with Sunn hemp (Crotalaria juncea L.). Since 2014, we’ve been conducting cultural studies with this promising cover crop, investigating best management practices for Wisconsin conditions including planting date and rate as well as seeding ratios with sorghum-sudan, another warm season species, for planting in a mix. We learned early on that it was a beetle attractant, a potential problem to be aware of, but not the degree of attractiveness, and frankly, what doesn’t attract them?
That changed this past year when we initiated a new trial, part of our organic no-till work, which contained both Sunn hemp and buckwheat as treatments. We’ve long known members of the buckwheat family including smartweed are strong attractants and preferential attractiveness of buckwheat over other cover crop species is documented in the scientific literature. I also have firsthand experience: a few years ago we planted a cover crop demonstration at a well-known botanical garden, the beetles mobbed the buckwheat, left the others alone, devoured the plot then moved on to the rose garden. Guess what, I was not invited back the next year but a small price to pay for learning to watch for beetle attractiveness. This year, a great year for beetle abundance in East Troy I started watching the plots on an almost daily basis as soon as they started to emerge and never saw a beetle in the buckwheat plots BECAUSE they were all in the Sunn hemp. We had a similar experience at our demonstration plots at Farm Technology Days near Marshall. While this is one year’s observation, certainly not enough for scientific conclusion it’s enough for me to crown the champ.
The upshot: we still don’t know if this will impact the potential of Sunn hemp as a cover crop. My guess is the level of defoliation does not significantly impact biomass yield (I smell another study!) but if it does it probably doesn’t matter because with biomass yields above 6 tons per acre, this is by far the most productive legume we currently have. The question is the impact on other crops which needs to be investigated. For agronomic crops, I could see this being a field border issue because beetles are attracted to sod for egg laying and the only real concern is silk clipping in corn. Small scale vegetable production is another story because of close proximity of cover crops and attractive vegetable crops in the same year. That being said, I see potential to use Sunn hemp as a border trap crop to draw the beetles to the perimeter at emergence and manage them while the population is concentrated. I smell another study, stay tuned.
Photo credit: Mimi Broeske, UW-Madison