It’s a farmer’s worst nightmare: a healthy and promising crop devastated. A flourishing crop is ravaged by pests. The farmer struggles to combat the invasion while maintaining organic integrity.
Insects, weeds and plant disease are common pests that farmers battle to ensure a prosperous and healthy crop. Under organic production, farmers often turn to biological control or plant-based solutions to combat these threats to their crops. In recent years, these pest control methods have experienced remarkable growth around the world. Despite this promising growth, many plant-based pest control treatments are not registered for use in greenhouse or field crops. A team of researchers working in Organic Science Cluster 3 are working to change that.
Dr. Simon Lachance, a researcher at the University of Guelph, and his team are looking for biopesticides to control greenhouse pests. Also known as biological pesticides, biopesticides are based on chemicals derived from natural sources, such as bacteria, fungi, viruses, plants, animals and minerals. Biopesticides are generally more environmentally friendly than synthetic pesticides and most are acceptable under organic management standards.
“The goal is to extract biopesticides and then use them to control insect pests, particularly in greenhouses,” Dr. Lachance explains. “Our research is focused on greenhouses as there is extensive production of greenhouse vegetables in southwestern Ontario.”
Dr. Lachance’s research focuses specifically on extracting saponins from tomato residue. Saponins are chemical compounds produced by many plants, including tomatoes. These organic molecules produce a foamy quality when agitated in water and also have a bitter taste.
“In our work, we extract the saponin molecule from tomatoes, specifically from agricultural residues that are not used, such as tomato peels from tomato processing industries,” Dr. Lachance explains.
Another source of saponin is the leaves, stems and crop waste from tomato greenhouses. Since tomato vines are slow to compost, many greenhouses send them to landfills. Using the vines for saponin extraction has the added benefit of diverting organic waste from landfills.
“It has been known for quite a long time that saponins can be used as an antifungal agent to control certain fungi, including pathogenic fungi, and certain insects, such as aphids,” Dr. Lachance says. “One goal of our project is to reuse crop residues and agricultural waste, add value to them, and extract saponins to control insect pests in greenhouses.”
Once extracted, the saponin solution is applied to plants in various doses by drenching the soil if it is to be used as a biofungicide, or by spraying the foliage as a bioinsecticide. Currently, Dr. Lachance’s research team is analyzing its effects on tomatoes, cucumbers and peppers. Plants treated with saponins are then assessed for their effect at controlling insect pests.
“Part of the project is also to see if the plant responds by producing more defense proteins so it’s better protected, more resistant, against insect pests,” Dr. Lachance explains. “Saponins also have a repellent and toxic effect against certain insect pests. So, a foliar application has a biopesticide aspect that will probably prevent insects from feeding on the leaves and may also affect directly the insects present on the leaves.”
Dr. Lachance’s saponin research is currently targeting the tarnished plant bug, the melon aphid and mealybugs. In the lab, the team places approximately 10 insects on the leaves treated with saponin and observes what happens. They record whether the insects feed on the leaf and also record mortality rates to determine if there is a repellent or toxic effect of the saponin.
“We count the number of insects on the leaves every hour for about 24 to 48 hours,” Dr. Lachance explains. “Right now, we’re doing lab tests on leaves that are detached from the plants we grow in the greenhouse If there isn’t much of an effect in the first few hours or in the first 24 hours, there probably won’t be any long-term effect. If it works well, we will do more long-term testing, and in a greenhouse environment.”
As their research enters the third year of the five-year research activity, Dr. Lachance notes that they have uncovered promising results. In the laboratory testing stage, the team has recorded positive results of saponin extract that can partially repel the melon aphid. They are beginning testing on the mealybug. They’ve tested saponin extracted from tomato peels and residue from the shredded vines, leaves and stems. They also are planning to test potential synergistic effect of adding an essential oil with the saponin, and try various formulations that could increase efficacy.
While the goal is to manage pests, it’s essential to ensure that the plants aren’t harmed. Dr. Lachance explains that they conducted tests “to make sure that the biopesticide is not toxic to the plant. We apply the saponins on the leaves of greenhouse crops, and are measuring phytotoxicity over several days.”
The concept of saponin as a biopesticide isn’t entirely new. There is currently a registered saponin to control certain fungi in potatoes, soybeans and dry beans. While it is a registered biopesticide product, this saponin does not come from crop residues like the one Dr. Lachance is investigating.
The ultimate goal of Dr. Lachance’s research is to register the saponin extract as a biopesticide for use under organic greenhouse production. He aims to eventually submit a product to the Pest Management Regulatory Agency for registration. Although this process takes time, Dr. Lachance and his team are on their way to providing a solution for helping organic crop farmers manage destructive pests using plant-based extracts.
(OSC3) Originally published in Organic Science Canada magazine, Issue #3, Spring 2021
