Pest control potential in agricultural waste
How’s this for closing the loop? Researchers are testing different agricultural plant wastes as potential solutions for managing common greenhouse pests.
September 7, 2021 By Melanie Charbonneau and Dr. Simon Lachance
Insects and pathogens are two challenging pests that growers tackle on a daily basis. For organic producers, there are even fewer options available.
This is where plant-derived biopesticides can help.
Plants produce valuable bioactive phytochemicals that are found in
appreciable quantities in plant waste. They can be less toxic than synthetic pesticides, break down safely in the environment, target specific pests, and be effective in small quantities. They can also be used as part of an IPM program to help reduce the chances of developing pesticide resistance. Following the extraction of bioactive phytochemicals to use as biopesticides, the remainder of the plant could be further composted.
Dr. Simon Lachance and his team at the University of Guelph Ridgetown Campus are investigating the use of tomato plant waste extract and hop essential oil as methods for insect and fungal pathogen control. Together with research partners Dr. Rob Nicol from Lambton College and Dr. Ian Scott from Agriculture and Agri-Food Canada, the group has tested these substances against the tarnished plant bug (Lygus lineolaris), the melon aphid (Aphis gossypii) and the long-tail mealybug (Pseudococcus longispinus).
Tomato crop vine residues were collected from Erieview Acres in Kingsville, Ont., and tomato processing wastes (peels) were collected from ConAgra Foods Inc. in Dresden, Ont. for extraction. Researchers then applied various doses of the extracts or oils on tomato, cucumber and pepper leaves and observed the insects in the laboratory as well as in the greenhouse. They observed whether the insect was mobile or immobile, on or off the leaf, or dead. The researchers were interested in whether the extracts caused mortality, impacted insect behaviour and/or had a repellent effect on the pest.
Saponins from tomato waste
One objective was to determine the efficacy of saponins extracted from tomato vine and peel residues in controlling key insect pests in greenhouse production.
As a bioactive component, saponins are organic compounds that can be found in varying concentrations in many plant species. They can be extracted from tomato plant waste, such as vines from greenhouse cleanouts or peels from the canning industry. Saponins have surfactant qualities, with the ability to interact with cell membranes of pests and disrupt the outer cuticle of insects. There is a saponin registered to control certain fungi in potatoes, soybeans, and dry beans, however, the pesticide is not derived from crop waste and does not target greenhouse pests.
Using the tomato extracts in doses of 200 and 400 mg/ml, initial results against the tarnished plant bug showed repellent effects for up to five hours but did not lead to mortality. For the melon aphid, doses of 100 and 200 mg/ml of tomato extract resulted in greater than 60 per cent reduction of the individuals present on the treated leaf over a period of 24 hours, demonstrating a significant repellent effect as well as up to 70 per cent mortality.
Hop essential oil
As a natural product for insect control, essential oils have increased in use over the past 15 years. There are multiple registered pesticides that contain essential oils as an active ingredient for the control of insects and diseases in crops.
Hop vine waste is being investigated by the team as a source of essential oil and bioactive components. In addition to phytochemicals that can be toxic to insect pests, hop essential oil contains an alarm pheromone (ß-farnesene), which is naturally released by aphids when attacked by predators. Exposure to the alarm pheromone can lead to avoidance behaviours, such as dropping off the plant or walking away. The resulting movement can then make it easier for biological control agents to seek out and control the aphids.
In our tests, hop essential oil had a repellent effect against the tarnished plant bug for up to five hours at low doses of 5, 10, and 25 mg/ml. The repellent effect lasted longer at higher doses of 50, 100, and 200 mg/ml. Mortality reached up to 50 per cent at the highest dose of 200 mg/ml.
When used against the melon aphid, few individuals remained on the leaves at doses of 25 mg/ml or higher over a period of 24 hours. In addition to a significant repellent effect, there was more than 97 per cent aphid mortality at the two highest doses and above 66 per cent mortality at 25 and 50 mg/ml.
When combined, the tomato extract and hop essential oil improved the inhibition of fungal pathogen growth.
The team tested the effects of tomato, hop and pea extracts against thirteen plant pathogenic fungi, many of which cause damping-off of seedlings, including Fusarium graminearum, Phytophthora parasitica, Rhizoctonia solani and Pythium irregulare. These mixtures were found to be generally antifungal, but differences in susceptibility were observed between the various fungal species tested. Notably, growth of Pythium irregulare was inhibited by up to 62 per cent relative to the control (untreated) treatment when both the tomato extract and hop essential oil were combined.
Before these products can be registered for use, there is a need to first understand their effects on other organisms in the greenhouse.
Currently, the phytotoxicity of the extracts and the essential oil are also being tested when applied to the crop’s leaves, to ensure that there is minimal effect on the health of the plant while maintaining a good level of insect control.
There was mild phytotoxicity observed in applications of 25 mg/ml of the tomato extract, with damage increasing in doses 50, 100, and 200 mg/ml. A modified formulation of saponin may decrease phytotoxicity and increase efficiency, and will be tested at a later date.
Future studies will assess the impact of these natural products on biological control agents used in greenhouse production, as well as test combinations of these products against insect pests to evaluate potential synergistic effects.
At a time when sustainability is more important than ever, pest management solutions using waste products presents an opportunity to ‘close the loop’ and focus on a circular economy. The practical end goal, nonetheless, is to develop low-risk biopesticides for use in greenhouse production.
This project is funded by the Organic Science Cluster III, Ontario Greenhouse Vegetable Growers, and Weston Seeding Food Innovation. Industry partners include Erieview Acres in Leamington, and ConAgra Foods Inc. in Dresden.
Simon Lachance, PhD, is Assistant Dean Academic and Melanie Charbonneau is a research technician at the University of Guelph Ridgetown Campus. For more information, contact Dr. Lachance at firstname.lastname@example.org
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