Small scale gas weeders

Previous articles on “thermal weed control” in these pages have concentrated on larger scale tractor-mounted and commercial-scale municipal implements

I recently borrowed a small gas unit from E H Cambridge & Co, at Mount Barker, to evaluate the tool for small scale weed control.

Our new property at Mylor has extensive gravel driveways and parking areas, which can become very weedy, and look very untidy. It also has brick paving (and the inevitable weeds which grow from the cracks) and fencelines — a curse for weed control in any situation. Although we have made extensive changes in less than one year since we moved in, including removing large areas of environmental weeds, we have so far avoided the use of any herbicides. Although there is plenty to do, and herbicides sometimes look like a timesaver, we will struggle to find non-toxic methods for all our problems, and hope to run the small property completely on organic lines.

Gas fuelled flame weeding offers a good option for the gravel and brick paved areas. With some reservations, it will be suitable for work on the fencelines.

The tool consists of the following components:

• A 9 litre gas bottle (you can fit any size, but 9 litres seems to be a good compromise between weight and convenience — that is, not having to stop too often to refill

• A gas regulator, to keep the flow reasonably constant, regardless of wether the bottle is full or nearly empty

• A flexible hose approximately 2.5 metres in length

• A handle with a trigger device

• A short brass tube, to provide security from burning and extra handle space

• A gas spreader, to spread the flame

• An ignition source, (which could be a cigarette lighter).

I found an old trolley, similar to a sack truck, for $12 in a second hand yard. It works well to transport the gas bottle around the yard, especially for Amber, who is quite small and would find the whole unit heavy to lift and control.

The following points of interest are noted, from using the weeder about three times over the paths and driveways.

The handle provides inadequate grip, especially for a large hand. With a considerable weight at the end of the brass wand, only 20 minutes of work was enough to produce sore wrists. This problem was not lack of strenght, as I had been using a chain saw and potpuki (tree planter) extensively and was in top shape — it is because the handle is too thin. A pistol grip or wider handle would help greatly.

There are two positions, “on” and “boost”. It is necessary to use the boost position for most burning.

There is generally adequate control over flame length and intensity, with an adjustment possible at the gas bottle, the regulator, or by a small dial on the handle. The problem with the latter is that after twenty minutes or more the wand started to droop (due to poor grip). As it drooped the dial tended to roll over the fingers, and could be accidentally adjusted.

The flame spreader needs to be held about 40 centimetres away from the ground (depending on final adjustments). I fancy it works better if pointed slightly forward, rather than directly down. Placing the spreader too close to the target can blow the gas flame out from back-pressure. Also the hottest part of the flame is more dispersed when the unit is held close.

It was useful to start up the unit in evening light, to see the total flame. In bright light conditions most of the flame remains invisible. Once a picture of the flame shape was imprinted into my brain, I found control a lot easier to achieve.

The tool could use a flame guard if used around ornamental plants or under the skirt of fruit trees etc. Some plants, such as Camellias were quite sensitive to heat and browned off quickly. A gas weeder used in bananas by Mauri Franklin at Mission Beach is fitted with a home made guard, which stops most of the updraught.

Idea treatment for most small weeds was to flame over them once, leave about eight days and treat again. Leaving weeds longer than this increased the need for further treatments. A shorter interval did not produce enough new growth to control the second time.

It is necessary to hold the flame over large weeds for some time (30 seconds or more). Individual species vary greatly in their sensitivity to direct heat.

Flame works well on many small grasses and weeds. It was not very effective against weeds with large underground reserves, in bulbs, stolons or rhizomes, although temporary control is possible.

Beware of some weeds, which can produce noxious gasses when flamed. Ern Cambridge told me that it is possible to become drunk from chemicals given off by oxalis. I did not try this (we use good organic wines for this purpose) but I did notice strong odours from sour-sob and certain other weeds. Use the tool in the open and you should not be too badly affected.

Beware using the flame tools in hot weather. It was surprising how much difference air temperature and humidity made to the effectiveness of the flame on weed kill. These environmental factors also strongly affected the readiness of plant debris, such as bark and dry leaves to ignite. Watch the area treated behind you for a while after treatment to ensure that small fires are not fanned into larger ones. In some areas there will be significant seasonal limitations on the use of naked flame. Also be aware that the flexible hose can be damaged by the flame or small fires started by the tool.

Economy was reasonable. The total price of the unit was at least twice the cost of a good backpack spray unit and gas is more expensive than herbicide, for the area treated. Given the advantages of not using chemicals, I would recommend and use a tool such as this one.

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