Weed control is an ongoing problem for any agricultural operation. Since the first seed was planted, farmers have battled unwanted plants manually with a hoe, culturally with crop rotation and chemically with herbicides and fumigants.
As the price of petroleum-based chemicals increases and restrictions on chemical fumigants increase, researchers at New Mexico State University's College of Agricultural, Consumer and Environmental Sciences are studying alternatives to help agricultural producers in the ongoing battle with weeds.
Mark Uchanski, assistant professor in the Department of Plant and Environmental Sciences, specializing in vegetable physiology, is studying biofumigation as an alternative.
“Biofumigation is the natural process of intentionally using the bioactive, or biologically active compounds that can affect the growth and development of pests, properties of a plant and other organic materials to aid in reducing populations of plant pests in the soil,” Uchanski said. “Studies have shown that biofumigation works in other parts of the country; now I want to see if it will work in the desert Southwest.”
Uchanski's current research is focused on managing agricultural weeds using Ida Gold mustard, hairy vetch and winter wheat.
These crops are grown for several weeks, then tilled into the soil to release their bioactive compounds during decomposition, to help manage troublesome weeds such as morning glory and yellow and purple nutsedge in New Mexico's onion fields.
Determining the level of bioactive compounds, such as glucosinolates, in a plant is the starting point for selecting a good biofumigant crop.
“The mustard cultivar ‘Ida Gold’ has been bred for the specific purpose of being as ‘hot’ as possible,” Uchanski said. “If you chewed on the leaf of the plant you would have a very unpleasant experience - similar to eating horseradish. Plants that have a strong effect on the human taste system have an effect on soil pests. We are good at tasting the glucosinolates, which cause the strong flavors.”
When the glucosinolates combine with an enzyme, also in the plant cell, a volatile plant compound is released. In humans, when the plant is chewed up this very volatile aroma goes into the nasal passages and causes discomfort. In the soil environment the resulting compounds are what can inhibit the unwanted plants.
“Two conditions need to be present for the chemical reaction to occur - water and heat. The hot part we have. Water is the big issue. When you incorporate the plant material into a dry soil environment, all that will happen is that the material will dry out. They will not be biological active because there is not enough moisture,” Uchanski said of the challenges of making biofumigation work in the dry conditions of the Southwest.
Spring onions were selected for the study, because the weeds in the spring are very difficult to manage. The climate conditions - temperature and moisture - are perfect for other plants, not just the onions, to germinate and grow. The unwanted plants compete with the onions for nutrients, light and moisture.
For the biofumigation to work, the cover crop will be planted in the early fall, cut when the flowers come on about eight weeks later and then tilled into the ground.
“The glucosinolates are at their highest when the plant is blooming. Therefore, the residues are the most bioactive and we hope to see the most weed control,” he said. “The biofumigated field may lay fallow for a period of about six weeks over the winter, then onions can be sown the following February.”
To further introduce this research and alternative soil pest control technique, Uchanski has invited John Masiumas, associate professor at the University of Illinois at Urbana-Champaign, to visit NMSU this fall and participate in the Lowenstein Lecture Series. He will be presenting talks and seminars about biofumigation and its potential for the desert Southwest.
“Through our research, we hope to demonstrate that the cultural practice of biofumigating, with carefully chosen crops planted before onions, will give growers another weapon in the constant battle against weeks,” Uchanski said.