Illinois Researchers Explore Use of Sorghum-Sudangrass In the Battle Against Weeds

Researchers at the University of Illinois (U of I) are using sorghum-sudangrass as a summer smother crop in the battle against aggressive perennial weeds.

Perennial weeds threaten the sustainability of farms. Perennial weeds can establish from seed or extensive, deep creeping roots. They are vigorous and very competitive against annual crops. At field days and other events U of I researchers John Masiunas, Dan Anderson, and Abram Bicksler heard about the challenge organic farmers were having with perennial weeds, the worst being Canada thistle.

U of I Professor, John Masiunas, is a weed scientist of more than 20 years, with a strong emphasis on the ecology of weeds and weed seed bank management. U of I Extension Specialist Dan Anderson has a long research and outreach history in sustainable and organic agriculture. In 2007, the two researchers, along with a U of I PhD student, Abram Bicksler, submitted a proposal to the NCR-SARE Research and Education Grant Program and were awarded $144,003 to increase farmer knowledge and awareness of perennial weeds, and increase skills and practices in managing perennial weeds using integrated management approaches.

Research has shown that when sown at higher rates than normally used for forage crops, sorghum-sudangrass hybrids make an effective smother crop. Their seedlings, shoots, leaves and roots secrete allelopathic compounds that suppress many weeds. The main root exudate, sorgoleone, is strongly active at  xtremely low concentrations, comparable to those of some synthetic herbicides. In their research, Bicksler and Masiunas used Canada thistle as a model weed to test different strategies with sorghum-sudangrass grass as a warm-season cover crop.

Bicksler and Masiunas developed a set of practices which employed a “many little hammers” approach to controlling perennial weeds without chemical inputs. The approach utilized timely tillage and mowing, coupled with a warm-season grass cover crop.

In 2007, Anderson began working with from nine to twenty farmers each summer on environmentally friendly ways to control Canada thistle using sorghum-sudangrass. The principles and methods were taught to nearly 40 participating farmers in four Midwestern states over three years. Masiunas stressed that the Canada thistle problem is usually found in patches, and their management strategy was implemented where Canada thistle was present in patches.

According to Anderson, those farmers now have a tool for managing perennial weeds without the use of chemical agents, using the following integrated approach for Canada thistle:

1. multiple tillage or mowing of the weed patch
2. final thorough tillage of thistle patch in early June
3. heavy planting of sterile sorghum sudangrass cover crop
4. mowing of sudangrass cover at 4 to 6 feet tall
5. allowing sudangrass to tiller and regrow
6. final mowing in late fall or leave standing cover until spring.

“Our project increased farmer, Extension educator, and scientist knowledge of key times during the life cycle of perennial weeds when the weeds are most susceptible to control,” explained Anderson. “It also improved knowledge of how sustainable management strategies can suppress perennial weeds.”

This was accomplished through online fact sheets, reports, presentations at farmer meetings, participatory on-farm research, farmer-to-farmer communication, and project participant co-learning. These outputs improved Extension, scientist, and farmer awareness of how integrated approaches can be used to manage difficult-to-control perennial weeds in sustainable and organic systems.

Through workshops, field days, and a mini-grant program they were able to share with farmers the results of their on-farm testing of research-based, chemical-free, thistle management practices. Farmers who participated in the project were paid a stipend at the beginning of the study and another stipend after they submitted a report. 
According to Anderson, results varied, but in general, farmers who closely followed the management plan and planted the sudangrass cover crop before mid-June reported excellent control of Canada thistle during the growing season.

“Our audience was sustainable and organic farmers along with Extension educators,” said Anderson. “We measured success through direct farmer feedback during summer farm visits by the project coordinator. Our project will, in the intermediate term, change farmer, Extension, and scientist behavior and attitudes toward managing perennial weeds. We believe the method developed here has very high potential to contribute to the sustainability of organic farmers struggling with Canada thistle. This weed can be so invasive and render some fields useless. An organic solution will save some fields and encourage some farmers that realistic solutions do exist.”

Presentations were made at the Illinois Specialty Growers Convention, and the 2009 Midwest Organic Production and Marketing Conference. Two field days were held in 2009, both featured organic farms. Perennial weed management was discussed at these events. A total of at least 130 farmers, advisors, and Extension personnel attended these events. In 2010, a presentation was given at the MOSES Organic Farming Conference. Project information was also presented at the organic transition session of Organic University.

“Canada Thistle (Cirsium arvense) Suppression with Buckweat or Sudangrass Cover Crops and Mowing” was co-authored by Bicksler and Masiunas, and was published in the October-December 2009 issue of Weed Technology.

Want more information? See the related SARE grant(s) LNC07-282, Best Sustainable Management Practices For Perennial Weeds.