Written by: Emily Cabrera
Expert Source: Nick Basinger, Assistant Professor of Weed Science, Crop and Soil Sciences

Cereal rye cover crop residue can be seen here between rows of cotton.

The Ninth Circuit Court of Appeals said earlier this month they are pulling registrations for the use of all dicamba products for row-crop production. This herbicide has been around since the late 1960’s, but became more widely used with the introduction of resistant cotton and soybean varieties in 2016 in response to growing weed resistance. The powerful herbicide has unfortunately been at the center of a lot of controversy since its utilization in field crops due to inadvertent drift onto sensitive crops. With the increasing loss of effective chemistries, either due to weed resistance or through legislation, growers need more tools to choose from when tackling economically threatening weeds. As we continue to face more erratic environmental conditions growers are faced with increasing challenges to an already challenging occupation.

“So, anything we can do to help create more consistency should help growers do their job better,” said Dr. Nick Basinger, University of Georgia Assistant Professor of Weed Science.

Basinger is leading a research group working towards integrated weed management in a number of systems in Georgia that examine the potential use of cover crops for commercial growers. One of the benefits of cover crops is their ability to suppress weeds, such as Palmer amaranth (Amaranthus palmeri), during fallow periods between cash crops by preventing weed seeds from germinating.  

“The goal of our work is to look at ways to manage crop and non-crop areas and try to take advantage of all the tools in the toolbox. Assessing what tools we have for each system, what tools we can potentially develop, and then where the strengths and weaknesses are for those tools, and what the ‘breaking points’ are, so that we can develop comprehensive management practices. This allows us to develop production systems to optimize weed management and gives growers the most advantage,” explained Basinger. 

Cover crops are widely used throughout the Midwest in a number of production systems, so a lot of this research is being adapted from those systems to fit our climate and soil demands in the southeast. While cover crops have already been successfully used by some growers in parts of Georgia, the implementation is slow among farmers as the body of research for growing cover crops in this region is still relatively limited. 

Basinger and his team have between eight to ten projects underway in the piedmont region of Georgia, with some of their work happening at the Midville Research Station. Multi-state projects looking at winter cover crops and summer cover crops will help researchers provide better recommendations for growers during those fallow periods between cash crops. Winter cover crops are usually planted in the fall after a cash crop has been harvested and will remain in the ground throughout the winter months. A summer cover crop is a quickly established cover crop that’s seeded between summer and winter cash crops to keep the ground covered and accumulate nitrogen. Summer cover crops have the potential to be used successfully in vegetable production because of the quick turn-around time before the next cash crop needs to go in the ground. Sorghum-sudangrass and sunn hemp are quickly established and rapidly put on biomass, making them great candidates for summer cover crops in Georgia.

“Once projects are well established in the piedmont, we will look to partner with growers in south Georgia,” said Basinger.

This is Basinger’s teams’ first year working with cover crops in cotton production in the piedmont. Because cotton is harvested later in the season his team is looking at the potential for cover crops to be used and perform well early in the season within this system.

“This research is actually partially funded by Cotton Incorporated, they are interested in looking at integrated weed management, which is very exciting,” said Basinger.

The winter cover crops used in this project are crimson clover and Wrens Abrusi rye. Basinger is also adapting and evaluating a living mulch (white clover) system in cotton, which is a spinoff from Dr. Nick Hill’s previous work in corn production.

Figure 1. (from left to right) Cereal rye, no cover crop, living white clover mulch, and crimson clover approximately 3 weeks after cotton planting. Areas in red indicate where Palmer amaranth seed was planted and will be monitored for suppression and reproduction over the next several years.
Figure 2. Aerial photo of the whole study which occupies approximately 1 acre at the J. Phil Campbell Research Farm located near Watkinsville, GA.

This research is the focus of Dr. Basinger’s PhD student, David Weisberger. Research plots were sown with a known number of Palmer amaranth seeds in the selected cover crop species plots, and bare ground treated rows are used as control plots for comparison. Research will evaluate whether cover crops can suppress weeds over time by quantifying weed suppression, emergence counts, rate of growth, and fecundity.

“The control plots are consistently full of weeds, whereas the cover crop plots are performing well because they limit the amount of light that weed seeds receive and reduce soil temperatures that are essential for Palmer amaranth germination,” explained Basinger.

Thus far, the team has observed the best results from the living mulch and cereal rye, but are examining other important tradeoffs that growers need to be aware of, such as water use requirements, shading issues, and potential for cover crops to compete for resources.

“Originally, our research started as a weed focus, but we quickly realized this has more facets that need assessment, so we’ve adapted this research to provide a multi-disciplinary approach” explained Basinger.

In addition to looking at cover crops’ potential to suppress weeds in cotton, UGA researchers Nandita Gaur and Matthew Levi are studying hydrology and infiltration rates and soil health parameters (organic matter, nitrogen, phosphorous, pore space). Weisberger and UGA Entomologist, Bill Snyder, are also looking at this project from an insect pest management approach.

“This is just one tool in the toolbox, it’s not a cure-all but we hope to demonstrate that over time, cover crops have the potential to increase yields, minimize weed seed banks, improve soil health, reduce erosion, and limit the amount of costly chemical inputs farmers need to apply for a successful harvest,” explained Basinger. “The beauty of this research is we assume all the risk and work out the problems first and then are able to disseminate that information to growers so they can make the best decisions for their specific operation.”

To learn more about what’s going on with Dr. Basinger’s research and stay up to date on what’s going on in the world of UGA weed science, follow him and his team on Instagram and Twitter (@ugaweeds).