WESTERLY — As of about two weeks ago the Public Works Department is packing heat. That’s heat in the form of a thermal weed killer.
The department bought one of the devices about two weeks ago for $2,900. On Tuesday Keith Birkbeck and Sam Debartolo, public works employees, used the device to kill weeds that were popping up in and along the sidewalk on Canal Street.
Birkbeck held the 5-foot-long lance and aimed the hot air diffuser at the weeds while Debartolo followed behind pushing a wheeled trolley that held a propane cylinder while Public Works Director Donald Ouellette looked on.
In some cases the weeds briefly flamed up. Ideally, Ouellette said, the system works without actually igniting the weeds. Instead, the heat should kill the weeds by destroying their cellular systems, including their seeds and roots. Actual burning could have a reverse effect by releasing nutrients in dead plant material into the soil, causing rejuvenated weeds to grow back stronger.
Ouellette, who started his job in late June after the retirement of former director Paul Corina, saw the device demonstrated during an American Public Works Association conference in Kansas City in August. Before getting the device, Ouelette said the department was applying herbicide once or twice a year, “but I was looking for something different.”
While the thermal system can be used by a single operator, Ouellette said he is inclined to use the two person approach that Birkbeck and Debartolo used on Tuesday. “There’s no chemicals and it’s more efficient because it gets to the seeds and the roots,” Ouellette said.
Unlike the chemical approach, Ouellette said one pass with the thermal unit should be sufficient.
The heat softens leaves on the weeds. Ouellette demonstrated by holding a heated leaf in his hand and applying pressure with his thumb. He left a fingerprint on the leaf, a sign, he said, that the process worked correctly. In a matter of days the weeds die, turn black, and blow away.
Ouellette said the ignitor device on the thermal unit has to be replaced about once per year. Ignitors cost about $50 from the manufacturer, Ripagreen, he said. The company makes a similar device for shrink wrapping.
The department focuses on weed removal in the spring and the early summer.
“The key is finding the time,” Ouellette said.