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does burning weeds kill the seeds in the fall

In addition, a thick layer of mulch reduces weed seed germination while conserving water. You can add a drip irrigation system to put water over the desirable plants’ and shrubs’ root balls while leaving the weed seedlings to dry up in the hot summer sun.

Weeds – the bane of nearly every gardener’s existence. While reaching for the Roundup is one option, you may consider burning weeds instead. Flame weeding is an organic method of weed destruction and removal, but be careful with the open flame. You don’t want to risk starting a wildfire when working in hot and dry conditions.

When using a flame weeder, you should put on closed-toe shoes, long pants, safety goggles and other safety gear as recommended by the manufacturer. Torching weeds is a matter of applying high heat but not actual fire. If flames are visible, you may be walking too slowly; dry plant matter or bark mulch is in the treatment area; or you’re holding the weeder too close to the weeds. Use caution when the weather is dry and/or windy to avoid starting a fire.

Torching Weeds in Rocks

If you’re using organic methods in the garden, flame torching is an approved method of weed destruction. The University of Minnesota Extension points out that flaming works best on young and broadleaf weeds, especially when applied at least twice per growing season.

An alternative to both Roundup and burning weeds is using cultural controls in the garden. Hand weeding and careful cultivation with a hoe around existing plants reduces the number of weeds in the landscape. However, digging deeply when removing existing weeds or adding compost and other amendments to the garden bed also exposes buried weed seeds, warns the University of California IPM Program.

When weeds are embedded in the cracks of concrete sidewalks and driveways or sprouting amid gravel mulch or walkways, using a flamer is one method of weed removal. Even if weeds have developed resistance to herbicides, flame torching affects the plants’ cell membranes with high heat. You aren’t actually “burning weeds”; instead, you’re disrupting the plants’ ability to function by the application of targeted high temperatures.

Glyphosate is the active ingredient in several nonspecific herbicide products, including Roundup. It is absorbed by the plant’s leaves and moves through the plant down to the roots to destroy the weed. As the National Pesticide Information Center points out, glyphosate interferes with the shikimic acid enzyme pathway, which prevents essential protein production in plants. It is nonspecific, so it will also affect nearby plants if you spray on a windy day.

Objective: To measure weed seed mortality in response to flaming in the field.

Propane usage will be recorded by weight using portable field scales, and will be used to estimate per ha costs for the flaming treatments. Thermocouples and a portable temperature recorder will be installed in each treatment to record the thermal dose.

Project objectives from proposal:

This project will include field experiments conducted at one farm in Maine, and another in Vermont. The on-farm studies will be conducted on a uniformly cropped weedy field following cash crop harvest. At each farm, in the fall of 2011, weeds will be flail mowed and four replicated strips will be subject to the following treatments: no flaming; flaming at 40 kg propane per ha; flaming at 80 kg per ha; and flaming at 160 kg per ha (note: a 20-40 kg rate would kill sensitive weed seedlings). In the spring of 2012, soil sampling and subsequent greenhouse germination assays will measure the weed seedbank in each treatment. Ten soil cores (6.5 cm diam by 10 cm deep) will be randomly chosen from each plot, bulked, and spread in greenhouse flats, and watered to encourage weeds to germinate. Seedlings will be removed monthly, followed by drying and crumbling of soil and re-watering (four cycles in total). To measure the contribution of fall flaming on weed management in the subsequent crop, in June of 2012 we will record weed density after the final cultivation event at each farm. Specifically, eight 0.5 sq. m quadrats will be censused in each replicate of each treatment. Weeds will be identified by species and counted.

In this project we aim to test the hypothesis that fall flaming can efficiently and effectively kill weed seeds on the soil surface. While flaming is widely used to kill small weed seedlings, and field stubble burning is known to kill weed seeds, we are not aware of any research in which flaming has been used to target seeds. This idea comes from the experience of Rob Johanson, a diversified organic farmer in Maine who, while flaming potato vines in particularly weedy fields observed smoldering weed residues and reasoned that he was likely killing weed seeds. He has further observed that flamed plots generally have lower weed pressure the following year. We aim to confirm this observation with a series of on-farm experiments evaluating three flame doses and their effect on the following season’s germinable weed seedbank and early-season weed seedling densities. Laboratory studies conducted with condiment mustard (Sinapis alba), indicated that a 900C propane flame required 3 sec. or more exposure to reach mortality levels of 80%; mortality was 100% at 5 sec. of exposure (Figures 1 and 2). Field studies will include higher temperatures to reduce the required exposure time, and will evaluate the combined stresses of flaming and overwinter mortality. Results will be shared with other growers during a Field Day and a session on “Managing the Seedbank for Improved Weed Management” at the 2012 Maine Organic Farmers and Gardeners Association Farmer to Farmer Conference. We will also produce a short video on fall flaming which will be posted to our YouTube Channel (zeroseedrain), and the national eXtension website.

Performance Target: We expect that the germinable weed seedbank density will be inversely related to the propane flaming rate. Further, the spring seedling census data will proportionally reflect the effects of flaming on the germinable seedbank, with the lowest surviving weed density in the 160 kg per ha propane treatment, and the greatest weed density in the control treatment. Adoption of this promising management practice will depend on the expected tradeoff between faming cost and weed control benefits measured the following year.