Comfrey Questions

Chris Boerboom, Extension Weed Scientist

I’ve received a couple calls this summer asking for identification of a leafy green perennial with a large taproot (Figure 1.) The weed is comfrey and it is a very persistent, difficult to control weed. It had been planted in gardens in the past and was occasionally used as forage. Consequently, it appears in fields around Wisconsin, perhaps as old farmsteads are turned back into fields. Comfrey is most likely spread by tillage since root fragments can readily produce new shoots. Despite the showy flowers, comfrey seldom produces seed.

Comfrey is difficult to control with herbicides. However, Jerry Doll, Emeritus UW weed scientist studied comfrey control from 2001 to 2003 and he found that an integrated management program can be successful. Jerry Doll’s recipe for success is repeated here. 

“Comfrey can be conquered. The formula for success is to 1) plan to use a no-till system and glyphosate resistant crops for two seasons, 2) plant comfrey-infested fields last to delay the burndown application of glyphosate as long as possible, 3) apply a low rate of a soil-active herbicide with the burndown treatment, 4) plant 3 days after applying the burndown treatment, 5) apply 0.75 lb ae/a of glyphosate when comfrey is well into the flowering stage (probably mid to late June) and 6) consider preharvest glyphosate applications if necessary.”

If you are interested in more details on other herbicide options and trial results, an abstract of Jerry Doll’s research is available at this site: http://www.ncwss.org/proceed/2004/proc04/abstracts/178.pdf

Figure 1. Flowering comfrey shoots arising from thick taproots. These plants are close to 2 feet tall.