Flame Weeding in Organic Vegetable Farms

Researchers
Dr. Nabil Rifai

Background
Flame weeding has been a controversial issue since it was introduced 58 years ago in North America. Today it is a bigger topic than ever. The idea behind flame weeding is to kill weeds with an intensive wave of heat, without disturbing the soil or harming the crop root system. Since all plants are composed of tiny cells filled largely with water, a thin blast of heat directed at the stalk will boil the water within the cell. The pressure generated by this expanding water will then explode the cell it self, rupturing a cross section of the stalk. When this happens plant food and water cannot move from roots to leaves and the plant withers and dies.
     The trick is to apply heat when weeds are small. To accomplish this, three methods are used: Selective flaming, non-selective flaming, and pre-emergence flaming. In selective flaming the flame is usually directed across the crop row. If the crop is larger than the weed, with a more fully developed protective skin, the heat can kill the weed without damaging the crop. The heat is controlled by varying the speed at which the flame is passed over the field, and the position of the burner with respect to the plant. If the difference between protective covers of the crop and the weed are more critical, selectivity is obtained by directing the flame pattern towards the weeds and away from the crop. This is usually accomplished by parallel flaming or by using burners with more precisely controlled flame patterns.
     In many cases the stage of weed growth will be too similar to that of the crop to allow selective flaming. Under this condition non-selective flaming is applied to such crops on corn and onions. At an early stage of growth the terminal buds of these crops are still below ground. General flaming will kill both weeds and the tops of the crops, but the crops will sprout back from their terminal buds, usually with a head start on weeds. From this point on selective flaming can be used.
     The third approach, pre-emergence flaming, is less critical on all crops. If weeds have emerged before the crop they can be flamed back while the crop is still protected by soil. With weed growth retarded the crop can get a head-start. Selective flaming can then be used to keep the weeds under control.

Objectives
The purpose of this study was to: a) determine the efficacy of thermal and mechanical weed control on weeds in selected crops, b) compare energy requirements of the two control methods, c) determine the labour requirement for weeding and d) to compare crop yields.

Duration
This project was initiated in June, 1995 and completed in December, 1997.

Results & Conclusions
Results of this one year experimental work showed flame cultivation is a very labour saving and profitable support for the organic farmers. Growing seeded onions and carrots using flaming will be less expensive than traditional hand-weeding method; mainly since the labour cost for hand-weeding will increase . In onions, with pre-emergence flaming and post-emergence flaming at 15 cm. height, the labour requirement was lower than with just pre-emergence flaming method and considerably lower than with purely hand-weeding method, but flaming two times gave more yield reduction. In carrots the labour requirement was more than twice as much with the treatment with two hand-weeding than the treatment with pre-emergence flaming and two hand-weeding.
     Pre-emergence flame cultivation caused a slight yield reduction. Pre-emergence flaming involves relatively few problems even though the time of the treatment is very critical. Selective flaming in the growing crop, on the other hand, requires precision with great risk of damage to the crop plant. Post-emergence flaming have showed further yield reduction.

Potential Industry Benefits
Industry could benefit by the reduction of requiredman power which results in cheaper products, benefiting both the consumer and the farmer.

Partners
This project was funded by Organic Farming Research Foundation, Santa Cruz, California.