By Bob Fiorello, San Francisco Recreation and Parks (originally posted 7/19/2010)

Ok, so here we are- finally at the point in this three part series when we get to the good stuff. I’ve discussed some basic considerations in initiating a flame-weeding strategy and droned on about safety and regulatory matters. After all I’ve put you through, now it’s time to get down to what exactly flame-weeding can do for you and your park system. Yes, we are cooking with gas indeed. So let’s do this!

Before I get started though, it may be useful to point out some of the conditions and situations where this IPM strategy falls short or should be avoided altogether. Not to worry. This won’t take long and it could save you some time in the long run.

Timing is critical when it comes to weed-flaming. For one thing, fire safety officials may limit the practice to an official “burn” season. In the San Francisco Bay Area this roughly corresponds with our rainy season of late autumn through mid spring. So in a legal sense, flaming may not be a summer activity for many of us. That still leaves plenty of opportunity to address winter annuals and emerging summer annual and perennial weeds.

Along the same lines, green-flaming may be prohibited from use in non-irrigated natural areas and other similar sites where extinguishing an accidental fire can be too difficult to justify the risk. After all, who wants to be responsible for initiating a blaze that jeopardizes life and property? At all sites, one must also take into account things such as wind speed, the presence of dry leaves and paper trash, and other potential hazards.

There are a host of other practical, sensible considerations as well. Flaming should be avoided during times of high public use. Rolling out the propane dolly and torch midday to a play area overflowing with moms and tots is obviously not advisable. Perhaps an early morning start at such a facility would work out just fine. Above all, common sense should prevail in determining when and where to light up as it were. These possible scenarios will vary from place to place and should be addressed in training efforts tailored to your specific needs.

There are also physical limitations to the flaming technique to bear in mind. Weed flaming is only marginally effective on mature, perennial weeds. A burn down can be achieved but underground plant reserves such as rhizomes, tubers, and expansive root systems will not be affected.This is especially true for fire adapted plants such as many of our perennial grasses. In such cases flaming can have a “fertilizing” effect resulting in bigger weed problems later.

There is also the issue of the smoke and fumes produced during flaming. While the objective is to provide a quick pass to sear (and not BBQ) vegetation, smoke is still produced. Obviously, this is not a strategy to employ on toxic plants such as poison oak but what about the myriad of other weedy species out there? Unfortunately, there isn’t a lot of data to turn to in addressing this question. It is a good idea to avoid inhaling fumes produced when flaming anything to the greatest extent possible.

Now that that’s out of the way, let’s turn to the true benefits of the flame-weeding technique.

Overall, this strategy is very effective at managing young, emerging vegetation. Winter annuals and early appearances of summer annuals and perennial weeds are the true targets of the green flamer. The method can be more effective than hoeing, cultivating, and even spraying in this regard. Keep in mind that a quick pass to sear vegetation is what we are after here. This technique leads to a sort of “slow” kill as cell walls collapse, contents ooze out, and the affected plants wilt and wither away- unable to recover. The effect is similar to smothering young weeds with a deep layer of mulch as opposed to chopping them off at the soil level and thus initiating potential re-growth.

The technique takes practice and a bit of a leap of faith.The so called “thumbprint” test often referred to in training materials is a legitimate guide to assess a proper dose of heat. Flame a broadleaf plant like plantain and then press a leaf between your thumb and fingers. If you leave a good impression of your thumbprint you are right on track. Remember that the idea is to heat up and not burn down weeds. Over application simply wastes fuel, increases risk of fire, and reduces the level of true weed control.

Flaming is a no-till practice as the soil is not disturbed during the heating process. This can suppress withdrawals from soil seed bank reserves and protect soil organisms. So flame-weeding is particularly useful in seed bed preparation like in terms of turf renovation. Remember the old adage Sprinkle, Spray, Seed. Simply replace Spray with Sear and you’ll be on your way.This is a great and convenient way to follow up tilling, amending, and leveling practices- anytime soil’s been disturbed. A little water and time usually results in a fresh crop of weeds that flaming easily takes care of. Whenever possible, hit weeds at the cotyledon stage for best results.

Green-flaming can be performed right before, during, and after rain or irrigation. Other practices such as cultivation can lead to soil compaction and other problems when it’s wet and there’s no need to worry about runoff (of herbicides) issues here. Combine this with the fact that flaming is hard on winter annuals and spring weeds and you see why flame-weeding is the IPM method of choice in areas with a mild winter rainy season. Likewise, the method is great in and around water features such as ponds and lakes where pesticides may be prohibited due to wildlife concerns. One still has to be on the lookout for nesting sites etc. but the method won’t heat up or otherwise adversely affect the water.

Flame-weeding is very popular for managing weeds in the hardscape.Weeds growing in pavement cracks and expansion joints can be difficult to deal with without chemicals. Repeated flaming can cleanup such areas and hold them in check prior to caulking or other long term remedies. Additionally, the technique is useful for managing small weeds in soft pavements such as gravel beds or decomposed granite.

Flaming can be employed as a mowing technique for edging and along fence lines. While grasses treated in this fashion will likely recover, the need for follow up may be less frequent than that of string trimming. Flame-weeding also eliminates problems of tangled line along jagged cyclone fencing. When performed correctly, the method is safe and effective for managing tree wells and can be used in close proximity to woody plants. It’s a good idea to practice flaming for a while in more open areas to get familiar with the equipment before taking on such tasks.

Another benefit of flame weeding is its potential to destroy weed seeds in addition to vegetative growth. A troubling invasive weed problem of particular concern in San Francisco coastal areas is the African perennial grass Ehrharta erecta. This introduced species has really taken hold here and is both a nuisance to gardeners and a real threat to native habitats. It produces a remarkable amount of tiny seeds very quickly, making control efforts extremely difficult. Flaming can only kill very young Ehrharta seedlings but it can do a real number on emerging and developed seeds. In cases like this with mature weeds, flaming can be performed first to address this seed issue and later followed up with other methods to remove the weeds.

In addition to weeding applications, torch flamers are useful to have around for other stuff too. We’ve used them to remove yellow jacket nests and they’re great for destroying pathogens like those encountered in quarantined nursery stock. I won’t get into that here but trust me; flaming infested potted plants can satisfy demands of state officials concerned with pest outbreaks. Of course, in colder climates your torch is a handy tool for melting snow and ice and wherever you live, it’s a real party favorite at the workplace barbeque. You can basically get a large charcoal grill ready for cooking in about five minutes with a propane torch. This of course is important in getting the crew back to work in a timely manner, in addition to being a lot of fun.

So, I’ve pretty much exhausted my flaming material at this point. I hope this information has been useful; especially to those of you who may be currently considering the pros and cons of initiating a weed-flaming program. I personally believe that this is a valuable, sustainable practice that can play an important role in many park management scenarios. Green-flaming certainly has its limitations, risk factors, and other drawbacks.This is no cure-all for what ails most of us out there by any means but it may be part of a larger IPM solution to our shared weed problems.

Don’t forget to check out some of the links from my first post on this subject to learn more and see the technique in action. There’s plenty additional information out there on the internet and some pretty funny, if not relevant, weed torch videos to be found on YouTube. I am sure we’ll be posting some videos of our own on this subject at SPIN shortly and we’d love to hear from you on your thoughts on and experiences with flame weeding.Until next time, just remember, if weeds in your park are getting you fired up maybe it’s time to fire up your weeds. Here’s hoping that there’s fuel in the tank and a breeze at your back. Happy flaming!