Finding a New Way to Control Weeds in Cotton.

Sarah Chu

Sarah Chu

FFAR Fellow, Texas A&M University

College Station, TX

  • Soil Health

A common thread in farming is the concern about feeding more people. Yet rarely do we ask: How are we going to continually clothe people?

Cotton, Inc. looks to support researchers and farmers everywhere to continue to grow cotton. They are currently supporting my research at Texas A&M University, where I work to understand how to manage weeds that plague the $5.2 billion cotton industry in Texas.

Currently, herbicides are the main way to control weeds. But resistance to these herbicides has increased by 57% since 2000.

Weeds can be categorized by their prolific seed production, which allows them to spread through space and time, lying dormant until the time is ripe. Farmers face a known enemy — weeds — that has become resistant to one of the easiest ways to be killed: herbicides, meaning farmers need new ways to kill weeds and their seeds.

In some crops, such as soybean and wheat, farmers can inadvertently harvest weed seeds during the harvest of the crop. Farmers use combines which thresh and sieve the trash part of the crop from the wanted parts of the crop. The wanted crop parts are put into a grain cart, which is then taken to a processing facility. The trash parts of the crop are spread back onto the field. While this is effective in recycling nutrients, it also leads to an effective distribution of weed seeds. Currently, the only options to control weeds at harvest is herbicide control or hand removal of weeds.

Some farmers saw an opportunity to change the combine from being a weed seed spreader to a weed killer by manipulating the trash during harvest. Harvest weed seed control (HWSC) presents an option to remove the weed seeds with the combine while harvesting the crop. The crop seed is separated from the weed seed and killed or manipulated before being spread back out onto the field. HWSC has the possibility to manage weed seeds in farmers’ fields; however, there are some challenges in the adaptation of this technology to U.S. agriculture systems. HWSC may only be applicable to certain crops in the U.S. because a specific type of combine header is needed. Climate can also play a complicated role in harvest weed seed control due to the influence of crop moisture content and environmental conditions. Nationally, weed researchers are looking at how to implement different forms of HWSC such as chaff carts, bale direct systems, narrow-windrow burning, chaff or tram lining, and impact mills. More information about these alternatives can be found at

Sarah with cotton stripper in cotton field.
Sarah with cotton stripper in cotton field.

My research is looking at harvest weed seed control tactics and to determine how they can fit into cotton systems in the U.S.

To narrow down what method to use we first need to identify how cotton harvesters interact with weeds and their seeds in the field. Cotton can be harvested in two different ways: with a picker or a stripper. Pickers and stripper harvesters are used in different places throughout the U.S., with the main differences being the amount of unwanted items, such as leaves and stems, that end up in the harvest. To identify where the weed seeds are ending up, we target Palmer amaranth, a prolific microscopic seed-producer weed, and track the harvest by each Palmer amaranth plant with either a picker or stripper harvester. This allows us to determine on a per plant basis what ratio of weed seeds end up in the cotton, what amount has shattered to the ground, or what portion stays on the maternal plant when using a cotton picker versus stripper.

By determining where weed seeds end up during cotton harvest, we can then start to manage them. Weed seeds that are retained on the maternal plant can be targeted with other technologies to kill the weed seed, such as drones or stem shredding and the removal of the stems, a common practice to decrease insect pressure in cotton. Alternatively, weed seeds that are removed with the cotton to be processed can be targeted in the ginning process, resulting in material that can be re-spread on farmer’s fields for nutrient cycling.

Weeds are detrimental to cotton yields and need to be managed in sustainable ways, to keep us clothed while decreasing possible water contamination or soil loss. I am proud to be contributing to new ways to control weed seeds in cotton with the support of Cotton, Inc and am also grateful for their sponsorship for my participation in the FFAR Fellows program. As a fellow I am developing skills that can help me collaborate with and communicate my science to farmers to help increase adoption of these weed control tactics.

People collecting weed seed samples during cotton picking.
People collecting weed seed samples during cotton picking.
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