Farming, like many other industries, is ever evolving as new methods and technologies emerge to meet today's challenges. One of the most tireless challenges in agriculture is managing weeds, especially in vegetables like tomatoes.

Crops compete with weeds for their vital needs such as water, sunlight, and nutrients, causing a negative impact on crop yields and costs for farmers. Weed scientists develop multiple methods of mitigating weeds that farmers can use for their specific situation. These scientists are always on the lookout for solutions that have the broadest and longest lasting control with the least amount of time and resource input possible.

Herbicides, used in farming for decades, have limited effectiveness as weeds begin to grow around them, or become resistant to their affects. To reduce the need for chemical herbicides, researchers in the Mississippi Agricultural and Forestry Experiment Station, or MAFES, are testing non-chemical approaches to weed management including soil steaming, allelopathic cover crops, and biochar. The hope is to provide a viable solution for conventional and organic tomato farmers.

Dr. Te-Ming Paul Tseng, an associate professor in plant and soil sciences and MAFES scientist, explained that tomato crops are very sensitive to many commonly used herbicides. This limits the options for chemical use when controlling weeds in tomato fields. Beyond the crop's sensitivity to chemicals, weeds like Palmer amaranth have developed resistance to many herbicides, while others such as nutsedge, remain difficult to control due to the limited number of herbicides that are both effective against the weed and safe for use on tomatoes.

"The most problematic weed is often the one growing right next to your tomato plant. These resilient weeds can quickly take over a field, significantly reducing crop yields, and putting a strain on farmers," Tseng said.

A promising solution to this current issue is soil steaming. This technique of weed management uses high-temperature steam to kill weed seeds in the soil before planting crops. Steam is applied to the soil until the soil reaches a temperature of about 160 to 180 degrees Fahrenheit at a depth of four inches. This often takes about an hour using the tarp-steaming, or sheet steaming, method-where steam is applied to the soil surface and trapped under a tarp until the soil reaches the target temperature. Researchers are testing this method on 200 x 400-foot beds at the MAFES Truck Crops Experiment Station. The technique is shown to be effective, killing over 90 percent of weed species in tomato crops. The most stubborn weed, nutsedge, remains the biggest challenge even with soil steaming.

Soil steaming is a relatively simple process, which may prove to be more cost efficient than other traditional weed management methods. The process starts by prepping the ground to allow the steam to enter more readily. A woven sock that is connected to the steam pipe is then placed on the soil. The sock is then covered with a heat-resistant tarp to capture the steam which allows it to warm the soil. Results have shown that tomatoes grown in steam-treated soil tend to be taller and produce more fruit than plants grown under conventional circumstances.

"We will continue this research to confirm if our data are consistent, and we hope to relieve farmers of the strenuous process of managing weeds. This would be a huge reduction of cost because they won't have to purchase plastic mulch or herbicides anymore. When preparing their fields at the beginning of the season, all they would need to do is steam the soil beforehand and plant their seeds," Tseng said.

In addition to soil steaming, MSU researchers are studying the use of allelopathic cover crops and biochar for the management of weeds in tomato crops. Allelopathic cover crops naturally suppress weed growth through the release of chemicals in their roots. Allelopathy is a biological process that occurs in certain plants where they release allelochemicals into the air, which hinder crop growth and survival of surrounding plants. Therefore, the process of allelopathic cover cropping reduces weed populations.

Crops such as rye, wheat, clover, and hairy vetch are being tested for their weed-suppressing abilities. The cover crops are planted during the fall and are left to grow during the winter. Later, in the spring, they are terminated using a roller-crimper, creating a mulch that smothers the weeds and continues to release the allelopathic chemicals into the soil. The process creates a better environment for tomatoes to grow, by adding organic matter to the soil while also reducing weed populations. This method is particularly useful for organic farmers, where herbicide use is restricted. Additionally, the mulch created from cover crops reduces the need for plastic mulch which is a common weed suppression method in tomatoes.

Tseng has partnered with Dr. Shaun Broderick, an associate research and extension professor in plant and soil sciences, stationed at the MAFES Truck Crops Branch in Crystal Springs, where the research is taking place. The team has found that the use of biochar and soil steaming together has had a promising effect in tomato plant health. Biochar consists of carbon and ash and can be used to coat tomato seeds before planting. It has proven to protect seeds from herbicide chemicals. The use of biochar and soil steaming together could be pivotal for farmers.

Broderick, in particular, is excited about soil steaming and its potential to be more successful than traditional weed management methods.

"With soil steaming, we can control most weeds much better than other methods. We can control above 90 percent of weeds, excluding nutsedge. We use our steam generator that releases steam at 240° Fahrenheit. This method of weed management is very promising compared to the conventional processes we've been using," said Broderick.

Upon completion of the four-year study, researchers aim to share their findings on effective weed management strategies. Early results from testing steam applications on nutsedge are promising, and the team hopes to identify long-term solutions for weed suppression. The final results will be shared through field days and scientific journal articles, in hopes to bring valuable insights to the agricultural community.

"We steamed a plot in September of last year, and we've seen significant weed control nine months later. It's interesting because the weeds that did eventually come up were different than the weeds from before. There was a huge decrease in the number of weeds that appeared as well, compared to when we just used herbicides. Nine months of weed control from steaming is a great place to start," Broderick said.

Combining soil steaming, allelopathic cover crops, and biochar is an effective approach to weed management in tomato farming. Together, they reduce cost, enhance soil health, and improve crop yield, providing a sustainable solution for farmers. These methods together offer immediate and potentially long-term weed suppression, changing the dynamic of weed management in tomato crops.

This research is funded by Southern Integrated Pest Management Center and the Mississippi Agricultural and Forestry Experiment Station.