Fall Flame Weeding: Targeting weed seeds before they enter the seedbank
Controlled studies confirmed that propane flaming, at a speed of 0.6 mph or slower, killed at least 90% of the seeds of three weed species tested (wild mustard, large crabgrass and hairy galinsoga). Weed species varied in their response to flaming, with mustard comparatively less sensitive than large crabgrass and hairy galinsoga). Samples of on-farm flaming assays of test weed seed samples are being processed, and soil samples will be collected in the spring to quantify the weed seed bank following three flaming exposures.
Flaming can efficiently and effectively kill?weed seeds on the soil surface.
On-farm experiments evaluating the effects of three flame doses on the following season’s germinable weed seedbank and early-season weed seedling densities. We conducted extensive controlled-environment testing to develop dose-response relationships for three weed species. This work was not described in the original project, but was deemed necessary to provide background information for both conducting and interpreting field trials. As the workload for conducing these controlled experiments, and one field trial was greater than anticipated, a second field experiment in Vermont was not established.
1. On-farm Field Day (Goranson Farm, September, 2012)
2. “Managing the Seedbank for Improved Weed Management,” presentation at the 2012 Maine Organic Farmers and Gardeners Association’s Farmer to Farmer Conference (November 2012).
3. Video on fall flaming which will be posted to our YouTube Channel (zeroseedrain), and the national eXtension website (December 2012).
While we have collected images and video of our research to-date, and volunteered a session at the 2012 Farmer-to-Farmer conference, our outreach efforts will begin next year.
We initiated this project with greenhouse research to develop methods for measuring temperatures under propane flaming conditions. This proved more challenging than anticipated, as durable thermocouples were relatively unresponsive to a passing flame due to their large thermal mass. Several types of fine-wire thermocouples failed after only several exposures due to the high temperatures. Omega brand unsheathed fine-sire K Type (CHAL-010) were eventually found to offer both necessary durability and responsiveness.
Seed exposure under controlled conditions was a further challenge. The high pressure of the flame simply blew seeds out of the path, scattering them. To address this, we fabricated stainless steel mesh boxes, 4 x 4 x 1 cm, to contain the seeds.
We used a handcart mounted with a single propane burner to examine maximal temperature, propane consumption, and mortality of wild mustard (Sinapis arvensis), large crabgrass (Digitaria sanguinalis), and hairy galinsoga (Galinsoga cilata). Maximal temperatures ranged from 100C at 1.8 km/h to 1,000C at 0.2 km/h. As expected, weed species varied in their response to flaming. At the fasted speed of approximately 1 mph (lowest exposure), seed mortality averaged 17, 75, and 88% for wild mustard, large crabgrass and hairy galinsoga, respectively. All three species suffered greater than 90% seed mortality at 0.6 mph.
Field experiments were to be conducted at two farms, one in Maine and one in Vermont. Only the Maine site was completed, however, due to complications in conducting field temperature measurements and the need for repeated visits to this site. Field experiments included a replicated trial with three flaming speeds chosen by Rob Johanson, the participating farmer, measurements of temperature at various speeds, sampling of weed residues post-flaming, and exposure of seed of several weed species in the flame-proof mesh cages described previously. Germination assays have proven challenging due to high levels of dormancy in the control groups. Presently we are confirming established protocols for tetrazolium viability testing.
Impacts and Contributions/Outcomes
We have no products in this first year of the project, but have conducted controlled environment and field experiments demonstrating flaming effects on seeds, although at relatively high exposure rates achieved with a slow speed (0.6 mph or slower).
Post-doctoral Research Associate
University of Maine
5722 Deering Hall
Department of Plant, Soil and Environmental Sciences
Orono, ME 04469-5722
Office Phone: 8144045079