Giant and Common Ragweed - Weeds to Watch

CROP MANAGEMENT SOLUTIONS Giant and Common Ragweed - Weeds to Watch

What You’ll Learn...  Giant and common ragweed can be difficult to control in many reduced tillage corn, soybean, and cotton systems.  Early season emergence, rapid growth rate, large leaf area, and a prolonged emergence period give giant ragweed a competitive edge.  One giant ragweed plant per 3 foot of row can reduce corn yield by 65% and soybean yield by Figure 2. Giant ragweed seedlings. Ohio State Weed Lab Archive, The Ohio State University, Bugwood.org 80%.

Identification Giant and common ragweed are annual broadleaf weeds Weed Environment with male and female flowers on the same plant. Giant and common ragweed are native weed species that Common ragweed has a shallow, fibrous root system have become more prevalent and difficult-to-control in and grows 2 to 4 feet high. Seeds can begin germinating many reduced tillage corn, soybean, and cotton systems. in May, with 90% of the seedlings emerging by early Common ragweed thrives in low-fertility soils and is June.8 Cotyledons in both ragweed species are spoon- adapted to no-till crop systems. Giant ragweed is shaped. The first true leaves of common ragweed have adapted to an array of environments, including one or two deep clefts in each margin, forming lobes wastelands, roadsides, fencerows, floodplains, and fertile (Figure 1). Plants emerging in May can produce 30,000 soils. Giant ragweed has primarily been a problem in to 62,000 seeds. Seeds are dispersed by water, birds, Ohio, Indiana, Illinois, Wisconsin, Minnesota, and Iowa, burrowing animals, and humans. Buried seeds can but has expanded its distribution outside this area during survive in the soil for thirty-nine years or more. the recent years. A recent survey of the North Central Germination can occur at 50 to 80° F and soil moisture region determined that the spread of giant ragweed and of 14 to 22%. difficulty in managing giant ragweed was associated with reduced tillage, earlier and longer emergence period, Giant ragweed has simple, large, opposite leaves that and adaptation to field waterways.1 Giant ragweed have 3 to 5 deep lobes (Figure 2). Giant ragweed initially spreads from non-crop edge habitats to become emerges as early as March in northern areas, and can established in waterways and fencerows adjacent to crop continue to emerge into July. Giant ragweed is often 1 to fields and quickly moves into and becomes established in 5 feet taller than the crop. Giant ragweed plants can crop fields. bloom from July through October. Giant ragweed produces large crown-shaped seeds with points and ridges along the top of the seeds. A single can produce up to 5,100 seeds. Although seed production is relatively low, the energy reserves in the large, vigorous seed helps overcome the low seed output. Emergence, Growth, and Development Northern biotypes tend to germinate and emerge earlier than those from southern latitudes. Plants that emerge mid-April through May can produce more seed and biomass than plants that germinate in mid- to late June. Figure 1. Common ragweed seedlings. Ohio State Weed Lab Archive, The Ohio State University, Bugwood.org

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Synchronous, early-season emergence is characteristic of grow under weed-free conditions for two to four weeks both ragweed species in non-crop situations. Selection after emergence. Common ragweed plants growing in the pressure from row crop practices has resulted in a soybean row have reduced soybean yields up to 10 prolonged period of emergence for some giant ragweed percent when present at densities as low as four common biotypes.9 Historically, giant ragweed plants emerged by ragweed plants per 30 feet of row.4 the first of May. Recent research shows that giant ragweed Giant ragweed is a highly competitive weed in cotton, even in production fields can begin emerging as early as March. at low densities. University of Tennessee results show that Emergence can continue through June into late-July in 3 giant ragweed is more competitive with cotton than many eastern Corn Belt biotypes. Giant ragweed biotypes from previously studied weed species and more competitive Ohio, Illinois, and Iowa from non-cultivated areas had a than Palmer amaranth.6 large initial seedling emergence flush.10 Iowa biotypes in this study had a similar emergence period to the non- Management practices that promote a uniform, cultivated biotypes, but Ohio biotypes had a prolonged competitive canopy can help suppress the growth of emergence period. Illinois biotypes were a mixture of long ragweed and other weed species with extended 7 and short emergence periods. Results from this research germination periods. Soybean was planted in 15 inch rows suggest that the differences in problems caused by giant at densities ranging from 97,000 to 170,000 seeds per 7 ragweed across the Corn Belt may be due to differences in acre. The primary effect of the soybean canopy at higher genetically controlled emergence characteristics. The soybean plant densities was reduced weed biomass. prolonged emergence period may allow some giant Higher soybean populations helped reduce the potential ragweed biotypes to outlast pre-emergence soil applied yield impact of weeds escaping control and reduce the herbicides. number of weed seeds produced. Giant and common ragweed populations have been Competition with Crops confirmed for resistance to Group 2 (ALS) and Group 9 Giant ragweed has a competitive advantage over other (glyphosate) herbicides. weeds and crops due to its early season emergence, rapid Comprehensive weed management should include growth rate, large leaf area, and prolonged emergence scouting non-crop areas adjacent to production fields and period. Season-long competition from two giant ragweed in-crop to determine the appropriate pre-plant tillage or plants per 110 square feet can reduce corn yield by 13%.2 burndown herbicides plus sequential pre-emergence and Giant ragweed is more competitive in soybeans where one post-emergence herbicides for ragweed control. In corn plant per 110 square feet reduced yields by 50%.3 In Illinois consider TripleFLEX® II Herbicide, IMPACT®, Callisto® or research, giant ragweed was found to be three times more Status® herbicides. In soybeans, consider Rowel™ FX competitive than waterhemp.5 Ohio research showed that Herbicide, Valor® XLT, Fierce® XLT, Authority® First, or one giant ragweed plant per 3 foot of row reduced corn Authority® MAXX herbicides. For solutions and yield by 65% and soybean yield by 80%.5 When giant recommendations visit www.roundupreadyPLUS.com. ragweed plants emerge with the crop and interfere with Sources: 1 Regnier, E. and Loux, M. 2014. Spread of giant ragweed across the North Central region – results soybeans for at least 4 weeks, yields can be reduced more of a CCA survey. Ohio State University C.O.R.N. newsletter. 2 Harrison, S. K., Regnier, E. E., and Schmoll, J. than 25% if weather conditions are unfavorable for crop T., and Webb, J. E. 2001. Competition and fecundity of giant ragweed in corn. Weed Sci. 49:224-229. 3 3 Johnson, B., Loux, M., Nordby, D., Sprague, C., Nice, G.,Westhoven, A., and Stachler, J. 2007. Biology and development. In soybean, yield potential is protected from management of giant ragweed. Glyphosate, Weeds, and Crops series GWC-12. Purdue University Extension. most weed species if the crop has a 4 to 6-week weed-free 4 Jordan, T., Nice, G., Smeda, R., Sprague, C., Loux, M., and Johnson, B. 2010. Biology and management of common ragweed. Glyphosate, Weeds, and Crops series GWC-14. Purdue University Extension. 5 Hartzler, period after planting. However, giant ragweed may require R. 2004. Giant ragweed – revenge of a native. Crop Pest Management Short Course & MCPR Trade Show a 10-week weed-free period.3 Proceedings. University of Minnesota. 6 Barnett, K.A and Steckel, L.E. 2013. Giant ragweed (Ambrosia trifida) competition in cotton. Weed Science 61(4):543-548. 7 Hartzler, B. 2007. Power of the crop canopy. Iowa State University Weed Science online. 8 Common ragweed. Penn State University, http://extension.psu.edu. Common ragweed emerging with the crop can reduce 9 Schutte, B.J., Regnier, E.E., and Harrison, S.K. 2012. Seed dormancy and adaptive seedling emergence yields substantially but, similar to many other weed timing in giant ragweed (ambrosia trifida). Weed Science 60:19-26. 10 Hartzler, B. 2003. Giant ragweed species, is less likely to reduce yields when the crop can emergence patterns. Iowa State University Weed Science online. Web sources verified 12/15/2014.

Individual results may vary, and performance may vary from location to location and from year to year. This result may not be an indicator of results you may obtain as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible. ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. TripleFLEX® II Herbicide and Rowel™ FX Herbicide are not registered in all states. These herbicides may be subject to use restrictions in some states. The distribution, sale, or use of an unregistered pesticide is a violation of federal and/or state law and is strictly prohibited. Check with your local Monsanto dealer or representative for the product registration status in your state. Roundup Ready PLUS®, Rowel™ and TripleFLEX® are trademarks of Monsanto Technology LLC. Leaf Design® is a registered trademark of Monsanto Company. Impact® is a registered trademark of Amvac Chemical Corporation. Authority® is a trademark of FMC Corporation. Valor® is a registered trademark of Valent U.S.A. Corporation. All other trademarks are the property of their respective owners. ©2015 Monsanto Company. 140212013219 011415JSC.

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