Common ragweed is a shallow-rooted annual with variability in plant size, leaf shape, and the amount of hairs found on the plant. Its leaves are nearly smooth, thin, and finely divided into a number of lobes. Common ragweed can grow to more than six feet (or two meters) tall, branching frequently when populations are low.
Common ragweed is a summer annual and the most widespread of the ragweed species. It prefers undisturbed seedbeds and can thrive even in low fertility fields. Common ragweed is found in old pastures, wasteland, roadsides, stubble fields, and cultivated land – particularly in row crops. Glyphosate-resistant common ragweed populations have been confirmed in Ontario.2
Common ragweed spreads only by seed, with most germinating at or near the soil surface. Once in the soil, the seed can survive for years, waiting for the opportunity to germinate.1 If allowed to grow throughout the entire season, common ragweed plants produce an abundance of seeds. Small plants average about 3,000 seeds per plant, while larger plants can produce up to 62,000 seeds.1
Common ragweed’s smooth and finely divided leaves, as well as plant size, make herbicide coverage a challenge. It out-competes many other annual weeds and will reduce crop yield potential if not managed in a timely manner. Common ragweed is more competitive with soybeans than with corn. The estimated maximum yield loss at high weed density is 65% to 70% in soybeans.3
How to Outsmart Common Ragweed
- Scout early and often.
- Start clean and control common ragweed when it is small.
- Always use two effective modes of action on the target weeds to help reduce resistance selection pressure.
- Control weed escapes throughout the season and reduce the weed seed bank.
1 Weed Science Society of America: Dickerson, C. and R.D. Sweet. 1971. Common Ragweed Ecotypes. Weed Sci. 19:64-66.
2 International Survey of Herbicide Resistant Weeds Online. Internet. February 10, 2015. www.weedscience.org
3 Weaver, S.E. Impact of lamb’s-quarters, common ragweed and green foxtail on yield of corn and soybean in Ontario. 2001. Canadian Journal of Plant Science 81(4): 821-828.