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EVALUATION OF TWO METHODS OF THERMAL WEED CONTROL IN FRUIT TREE ORCHARDS, PESTICIDE SPECIAL STUDY, COLORADO STATE UNIVERSITY
Impact/Purpose:
Weed control without the use of synthetic herbicides is an expensive and time consuming task in perennial orchard/sustainable agricultural systems. Orchardists have few non-synthetic options available for weed control. A few naturally derived herbicides are commercially available, but they have biological and economical disadvantages for commercial growers. Currently, orchardists are employing two types of physical weed control; permeable landscape cloth and mechanical cultivation using devices such as weed badgers, Clement's hoe or flamers. The landscape cloth significantly reduces weed growth and competition. However, there are significant material and installation costs. Weed mat also harbors overwinterng rodent populations which feed on the trees and it is difficult to incorporate fertilizers or organic matter into the soil. The use of mechanical cultivation is also effective in controlling weed growth, however, during the cultivation process, tree roots near the surface of the soil are destroyed and adverse effects to soil organic matter and soil structures are likely to occur.
In the last decade researchers and growers have intensified research and adaptation of thermal methods of weed control. There are two basic designs of thermal weeders; direct flame and infrared radiant heat. Both methods rely on propane combustion to generate heat. Direct flamers utilize shielded burners which direct an intense flame on the plant surface. Direct flamers can generate temperatures in excess of 1900 degrees Centigrade. Infrared heat involves heating ceramic or metal surfaces to red brightness with a temperature of about 900 degrees Centigrade. This heat radiates onto the plants. Equipment costs for direct flamers are less than infrared flamers, however infrared flamers are considered to be more economical to operate (Parish 1990). In Swedish studies, Ascard (1998) concluded that a proper comparison between the two methods must take into consideration the weed species, plant size and the propane consumption per unit working width.
The principle of thermal weed control is to target the plant for less than one second with intense temperatures. The intense heat destroys plant cellular material, coagulating plant proteins, which disables plant respiration and normal plant functioning (Hewitt et al. 1997). There are several advantages to the use of thermal energy for weed control. Thermal weed control has been found to be equal to or nearly as good as that obtained by the use of glyphosate (Round-Up, Monsanto Corp., St. Louis, MO) (Hewett et al. 1997, Whitney, et al. 1971). In 2001, a direct flamer was observed to perform as well as herbicides in test plots located in an apple block in western Colorado (R. Zimmerman, personal observation). These plots included, field bindweed, Convolvulis arvensis L., purple mustard, Chorispora tenella (Pall.) DC., Canada Thistle, Cirsium arvensae (l.) Scop., wild lettuce, Lactuca serriola L., and common mallow, Malva neglecta Wallr. Herbicide tolerant plants such as field bindweed was not killed, but growth and biomass was significantly reduced.
Description:
Research Objectives: 1) Compare the efficiency of two different types of thermal flamers: a direct flamer (Red Dragon, Inc., LaCrosse, Kansas) and a prototype infrared weed flamer (Sunburst, Inc., Eugene Oregon) in controlling weed populations in an apple orchard. 2) Determine optimum tractor speeds and treatment intervals which would provide the best weed control with the most economical use of propane. Flamer heights will remain constant from ground level. 3) Compare the economics of two methods of thermal weed control with landscape cloth and mechanical tillage. The economics regarding the use of the landscape cloth and mechanical tillage already exists for use in western Colorado orchards.