June 19, 2009

Currently, organic food sales total $15 billion (2.5% of the food market). Interest in organic crop production is increasing among farmers and industry and additional farmland is shifting to organic production — about 4 million acres nationwide. As this market grows, so does the need to develop or extend efficient pest control methods.

Organic Weed Management

Organic producers rank weeds as their number one problem. Hand weeding and cultivation are the most popular physical methods used by organic growers for weed control; however, hand weeding is becoming cost prohibitive and repeated cultivation increases the chance for soil erosion and promotes emergence of new weed flushes.

In addition, only a few organic herbicides are approved for use in organic production, and they are expensive, costing as much as $1000 an acre. An alternative weed contol option -- using propane for flame weeding -- is being studied by UNL.

Flaming

During the flaming process, heat from the flame is transferred to the plant tissues, increasing the thermal energy of the plant cells and resulting in coagulation of cell proteins if the temperature is above 50°C. Furthermore, exposing plant tissue to a temperature of about 100°C for a split second (0.1 second) can result in cell membrane rupture, resulting in loss of water and plant death.

UNL Flaming Research

To learn how to optimize flaming as a weed control tool, we are conducting a series of experiments to obtain baseline information on crop and weed tolerance to broadcast flaming in Nebraska. A PhD graduate student, Santiago Ulloa, is studying and describing the dose response curves of propane for control of 12 major weed species and tolerance of six major agronomic crops. We believe that, depending on the desired level of weed control or tolerable crop injury level, a propane dose could be selected to either control the weed or reduce its growth, offsetting its competitive ability against the crop.

We use a custom built flamer mounted on an ATV. It uses propane and produces open flames. Four burners (LT 2x8) are placed 30 cm apart.

Based on the first year of data, broadleaf weeds and broadleaf crops were more susceptible to flaming than grassy species. About 80% control was achieved with a propane rate of 4 gallons per acre (GPA) for velvetleaf and pigweed, compared to using 8 GPA for barnyardgrass and 7 GPA for green foxtail. Barnyardgrass and green foxtail were not completedly killed and plants regrew in three to four weeks. Despite the regrowth, flaming provided early season control of both grassy species by severely reducing their growth, offsetting their competitive ability against the crop.

Similarly, corn and sorghum were less susceptible to flaming than soybean and sunflower. This difference likely results from the physical positioning of the species' growing point at the time of flaming. The growing point in broadleaf species was aboveground and exposed to the flame. In contrast, the growing point of grassy species during early growth stages was belowground and protected from the flame.

From a practical standpoint, flaming could be a very effective tool for managing broadleaf weeds and suppressing early season grass growth. Of all crops tested, broadcast flaming has the most potential for use in field corn.

We are continuing this research this summer. For more information contact the author at 402-584-3808 or email him at sknezevic2@unl.edu.

Stevan Knezevic, Extension Weeds Specialist
Haskell Agricultural Laboratory, Concord