Researchers look to control weeds in greenhouse propagation systems with steam and hot water
Seeds of several container weeds readily stick to plastic containers and germinate around the edge when old containers are reused. Notice the brown bittercress seed sticking to the container sides, along with germinating weeds.
Researchers are exploring ways to control weeds in greenhouse propagation systems with steam and hot water, according to an AmericanHort press release. The Horticultural Research Institute has endorsed the research project, with funding provided in part from the Floriculture and Nursery Research Initiative.
Weed control in propagation is difficult because it primarily occurs in greenhouses or other covered structures where herbicides are either not labeled or safe for use. Reuse of plastic propagation trays and containers exacerbates the weed problem. Seeds of many weeds, most notably bittercress (Cardamine flexuosa) and creeping woodsorrel (Oxalis corniculata), stick to plastic containers and trays, and are reintroduced into the production system when these containers and trays are reused.
To combat these challenges, Dr. James Altland and his colleagues at the Agricultural Research Service in Wooster, Ohio, have started documenting the critical temperature and exposure time needed for killing weed seeds with hot water or steam.
Their method would provide an alternative to soil solarization, a slow process that involves covering the ground with plastic to heat soil over several days or weeks. Research on soil solarization has established thermal killing temperatures over the range of 40–70 degrees with exposure times of hours to days. Use of hot water or steam would ideally use higher temperatures for much shorter periods of time — seconds or minutes.
Currently, there is no published information on how high the temperature or how long the exposure time must be to provide 100 percent control of weeds common in greenhouse propagation. So far, Altland’s research has found that creeping woodsorrel required exposure to 90 degrees for at least five minutes for 100 percent control. Bittercress was completely controlled with 90 degrees water at just one minute.
There is also evidence from some nursery producers that heat or steam will provide effective disease control. In Oregon, some nurseries have adopted the Grower Assisted Inspection Program to prevent the spread of the pathogen Phytophthora ramorum. Part of this program includes the use of hot water for killing P. ramorum on reused plastic by dipping it in a water tank at 80 degrees for 15 minutes. While this control point was intended to prevent the spread of P. ramorum, it has also proven very effective in reducing bittercress populations.
For additional information, please contact Jennifer Gray, HRI Administrator, at 614-884-1155 or jenniferg@americanhort.org.
