THE ISSUE:   Curlycup Gumweed

Curlycup Gumweed (Grendelia squarrosa) is a biennial or short-lived perennial weed common to pastures, rangeland, and other disturbed or non-managed sites. Chemical compounds (alkaloids, tannins, resins, and glucosides) found in curlycup gumweed make it undesirable as a forage and unpalatable to livestock. In high-selenium soils commonly found in southern Idaho, curlycup gumweed will accumulate toxic levels of selenium. Curlycup gumweed is extremely drought tolerant and will increase its’ population during drought conditions. In overgrazed areas, this opportunistic plant will take over bare ground and become invasive.

Curlycup gumweed begins growth with oblong cotyledons, then develops into a low-growing rosette arising from a stout taproot. In the second growing season, plants reach heights of 1 to 3 feet. Curlycup gumweed produces numerous branching, semi-woody stems with alternate, bright green, clasping leaves. Glands on the leaves secrete a gummy, resin substance, which gives the plant a sticky feel. Leaves are 1 to 4 inches long and have serrated edges. The flowers are 1 inch in diameter, yellow, disk shaped and form at the end of each stem branch. Curved bracts also secrete the sticky resin substance, giving them there “gumweed” name. Flowering occurs in mid-to late summer and lasts throughout the fall.

Integrated Pest Management (IPM) Options:  

• Cultural – Do not transport weed seeds on clothing or equipment; feed weed-free hay; keep ditch banks and roadsides free of seed-producing plants; do not allow young plants to establish. Establish healthy, competitive plant communities that are desirable and adapted to your soil and climate; fertilize pastures to outcompete curlycup gumweed; eliminate overgrazing in infested areas.

• Mechanical – Dig, hoe, pull, or till young plants, removing as much of the root as possible; tilling may need to be repeated; plants that are mowed or broken off will regrow. Mature plants are difficult to pull, so it is best to implement this control when the plants are young.

• Chemical – Broadleaf herbicides such as 2,4-D or dicamba are labeled for curlycup gumweed in landscapes, rangelands, pastures, and roadsides. Picloram, a restricted use herbicide, and mesulfuron may be used in pasture, rangeland, and noncrop sites. These herbicides provide excellent control when applied in the fall or early spring. Late season treatments on flowering plants do not provide satisfactory results. 2,4-D and dicamba are volatile during hot temperatures, so summer applications increase the risk of herbicide drift to nontarget plants. Always read and follow herbicide label directions!

Tom Jacobsen, University of
Idaho Extension Educator in Fremont County. (208) 624-3102 [email protected] and Justin Hatch, University of Idaho Extension Educator in Caribou County. (208) 547-3205