Is Mechanical Flame Weeding for Crops Growing in Popularity?

Flame weeding using propane is a USDA approved organic weed removal method. It affords an opportunity for organic farmers to save time and money in their weed removal efforts. Furthermore, propane prices are currently reasonable, as shown by the following ten-year price graph.

There are a wide range of human and tractor powered flame-weeder models, many hand-built by the farmer. Individual propane tanks with hand held wands are quite common, as are human powered push carts which can be wider and span rows.

The flame weeder is used for pre-emergent and post-emergent weeding. It is particularly useful for small crops which are slow to germinate, like carrots and onions. Since it avoids cultivation, it is a no-till method of weed control.

Red Dragon is one company which has designed commercial equipment for industrial thermal weeding. This method uses an average of five gallons of propane per acre, or about half the cost of herbicide application.

Row crop flame weeding was used back in the 1930s, using kerosene. Research using the method has been done on 30 to 40 different crops, with good results. The goal is to rupture the weed plant cell walls, something that can be accomplished in one-tenth of a second with exposure to flame. The gas pressure and ground speed are used to control the heat exposure. It is most successful in use against small broadleaf weeds two-inches tall or at the 3-leaf stage. It works well on morning glories or bindweed. Flame weed control is less successful on grasses and perennial weeds. If necessary, repeat flaming three to five days apart is better than a one time heavy flaming.

The University of Nebraska is undergoing testing using mechanical flamers, and is hinting at a possible growing interest among conventional crop producers due to RoundUp weed resistance. They are working with manufacturers to make four-, six-, eight-, 10- and 12-row units.

Safety is important when using flame weed control. The method should be used on a dry day, but not in extreme dry conditions.

You may also want to check out this video of a tractor mounted flame weeder working a field of carrots.

16 thoughts on “Is Mechanical Flame Weeding for Crops Growing in Popularity?

  1. rjs

    imagine that’d be a somewhat effective insecticide too…

    i used to go out at dusk after an all-day rain with a handheld propane burner to torch the slugs which would be climbing all over the plants by that time…

  2. MikeB

    Flame weeding is perfectly fine, for those who can afford the equipment and such.

    But it kills me — just causes me no end of belly-laughs — to think that “organic” gardeners view the use of a dwindling fossil resource such as propane as an “organic” method.

    Not much else points out the utter absurdity of “USDA organic certified” than propane-fired weeders. It’s a gas, as it were.

    1. K. McDonald Post author

      I understand your sentiments. The first time I saw a weeder like this (rigged up inside an old lawnmower housing) on an organic farm, I was taken back a bit. But, no one likes to hoe or hand weed much, do they? The row covers that everyone uses these days probably keeps the flame weeding to a minimum on small organic vegetable farms.

      1. MikeB

        “But, no one likes to hoe or hand weed much, do they?”

        Yes, I agree, and as I said I’d use a flame-weeder too if I could afford it–or if I even needed one (we grow one acre of mixed vegetables for CSA customers).

        The problem is the sheer absurdity of pretending to a more exalted “organic” style of farming using such techniques, especially as so many organics advocates can’t seem to keep their mouths shut about other farmers’ practices, about how “unsustainable” they are, about how “toxic” they are.

        I used to work at an organic farm, and while I have good memories of the place and its crew, I’m absolutely through with the organic movement and their casual hypocrisies.

        1. Jason

          Actually the “organic” referred to is that no chemicals are sprayed onto the plants and no residue is left either on the plants or on the soil. Heat IS an effective organic pesticide and has been used for decades.

          1. MikeB

            The problem, Jason, is that chemicals ARE sprayed on plants in organic agriculture, all the time, and I should know because I worked at an organic farm and had to be certified as a pesticides applicator to work there!

          2. MikeB

            By the way: The belief that there are “no residues” on organic food is a lie. According to the 2008 USDA Pesticide Data Program Report:
            43% of organic spinach samples were positive for spinosad
            (13 of 30 samples positive). And that’s just the beginning….

          3. Jason

            There are two Jasons commenting here so this may be confusing…Mike, while nearly ALL food has residues, isn’t it true that certified Organic foods have residue levels several times lower, both in terms of cumulative load and the average number of residue types per sample?

            So I feel like your statistic is taken out of context. And you set up a straw man, calling a “belief” a “lie.” Another way to frame this would be “Many buyers of Organic food believe there are no pesticides on the food, but this is incorrect. Even Organic food has some conventional pesticide residues on it.” The to be fair I would add, “However, these residues are many times less than on non-Organic food.”

          4. MikeB

            Jason, here is your statement:

            >>Actually the “organic” referred to is that no chemicals are sprayed onto the plants and no residue is left either on the plants or on the soil.<<

            Emphasis: "no chemicals," "no residue."

            Maybe it isn't consciously a lie, but it's as false as a lie.

            Now that you've changed the subject of "residue" levels: let's talk about that. The "loads" (a crappy unscientific term promulgated by the Environmental Working Group) on organic AND conventional a orders of magnitude below the tolerance set by the government standards, so the point is MOOT.

          5. Jason

            I understand your point about government levels on residues. Something public health researchers are struggling with right now are the potential impacts on developing fetuses and young children. Pesticide exposure tolerance is not set based on these populations and certain periods of brain and other key organ system development are apparently impacted by seemingly minute and formerly perceived as inconsequential levels of chemicals that mimic hormone signals. Also, no studies get at health impacts of multiple chemical exposure over a lifetime. So some medical/public health groups like Organic food for reducing exposure for those who eat the foods and by reducing the amount of pesticides in the broader environment.

  3. Matthew Platte

    A while back I was thinking about a steam setup. The advantage is that it could burn renewable wood which is somewhat plentiful around these parts. The downside is that it would require dragging water, fire and live steam to wherever the weeds are! :(

  4. Jason

    Kay, do you have any energy use comparisons for this versus other methods of weed control…herbicides, shallow tillage, manual labor, etc.?

    Even if people are used to weed by hand it takes energy to get them all there, put up a porta-potty, make sure they have fresh water and shade.

    1. K. McDonald Post author

      That was a question in my mind as I wrote this. While many at first glance might be horrified at this use of FFs to kill weeds, when one thinks about the FF inputs required to produce herbicides and get them distributed this method could be competitive, I’d expect. If CC is reducing propane’s use for heating homes these days, then perhaps more use to kill weeds is possible. Is this a method you would consider using?

      1. Jason

        I am in a curious exploration phase. We have 700 acres certified organic and weeds are my biggest concern for crops we are harvesting as seeds, such as clover, forage grasses, any grains, etc. Many of these are not row crops, we broadcast sow, or if they are sown in rows the spacing is tight so not sure if flame weeding is practical.

        The integration with livestock is important contribution for weed control. As long as weeds are patchy and don’t bother the entire field we can graze some of the seed crops and not take a seed harvest, or hay. One reason we got into sheep is that they are very good at eating weeds, better than cattle, and more economical than goats.

  5. Dan

    With all of the issues stated about being organic, I think most of you are forgetting your high-school chemistry class. Propane burns to form carbon dioxide and water. If not enough oxygen is present, it can also form carbon monoxide. However, in fields and gardens plenty of oxygen should be present. As a result, while unconventional appearing, would be EXTREMELY organic, if there can be such a thing.


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