Insects and pathogens are two challenging pests that breeders combat on a daily basis. There are even fewer options for organic producers.
Herbal biopesticides can help here.
Plants produce valuable bioactive phytochemicals that are used in
significant amounts in plant waste. They can be less toxic than synthetic pesticides, safely degrade in the environment, fight certain pests, and be effective in small amounts. They can also be used as part of an IPM program to reduce the risk of pesticide resistance. After bioactive phytochemicals have been extracted for use as biopesticides, the rest of the plant could be further composted.
Dr. Simon Lachance and his team at the University of Guelph Ridgetown campus are studying the use of tomato plant waste extract and hop essential oil as methods of combating insect and fungal pathogens. Together with the research partners Dr. Rob Nicol of Lambton College and Dr. Ian Scott from Agriculture and Agri-Food Canada, the group used these substances against the tarnished plant bug (Lygus lineolaris), the melon aphid (Aphis gossypii) and the long-tailed mealybug (Pseudococcus longispinus).
Tomato vine debris was collected from Erieview Acres in Kingsville, Ontario, and tomato processing waste (bowls) was collected from ConAgra Foods Inc. of Dresden, Ontario. for extraction. The researchers then applied various doses of the extracts or oils to tomato, cucumber and pepper leaves and observed the insects both in the laboratory and in the greenhouse. They observed whether the insect was mobile or immobile, on or next to the leaf, or dead. The researchers were interested in whether the extracts led to death, influenced insect behavior and / or had a repellent effect on the pest.
Saponins from tomato waste
One goal was to determine the effectiveness of saponins extracted from tomato vine and peel remains in controlling key insects in greenhouse production.
As bioactive components, saponins are organic compounds that occur in different concentrations in many plant species. They can be obtained from tomato plant waste, such as vines from greenhouse cleanings or peel from the canning industry. Saponins have surfactant qualities with the ability to interact with cell membranes of pests and destroy the outer cuticle of insects. It is a saponin registered to control certain fungi in potatoes, soybeans and dried beans, but the pesticide is not obtained from plant waste and is not effective against greenhouse pests.
With the tomato extracts in doses of 200 and 400 mg / ml, the first results against the tarnished plant bug showed a repellent effect of up to five hours, but did not lead to mortality. In melon aphids, doses of 100 and 200 mg / ml tomato extract resulted in a more than 60 percent reduction in the number of individuals present on the treated leaf over a period of 24 hours, which is a significant repellent effect and up to 70 percent mortality.
Hop essential oil
As a natural product for combating insects, essential oils have been used more and more frequently in the last 15 years. There are several registered pesticides that contain essential oils as an active ingredient in combating insects and diseases in crops.
Hop vine waste is being studied by the team as a source of essential oil and bioactive components. In addition to secondary plant substances, which can be toxic to pests, essential hop oil contains an alarm pheromone (ß-Farnese), which is released naturally by aphids when attacked by predators. Exposure to the alarm pheromone can lead to avoidance behaviors, such as weaning the plant or walking away. The resulting movement can then make it easier for biological control agents to locate and control the aphids.
In our tests, hop essential oil in low doses of 5, 10 and 25 mg / ml had a repellent effect on the tarnished plant bugs for up to five hours. The repellent effect lasted longer at higher doses of 50, 100 and 200 mg / ml. Mortality reached up to 50 percent at the highest dose of 200 mg / ml.
When used against the melon aphid, few individuals remained on the leaves for 24 hours at doses of 25 mg / ml or higher. In addition to a significant defense effect, there was more than 97 percent of aphid mortality at the two highest doses and a mortality of over 66 percent at 25 and 50 mg / ml.
In combination, the tomato extract and the hop essential oil improved the inhibition of the growth of fungal pathogens.
The team tested the effects of tomato, hop and pea extracts against thirteen phytopathogenic fungi, many of which kill off seedlings, including Fusarium graminearum, Phytophthora parasitica, Rhizoctonia solani and Pythium irregular. These mixtures were generally found to be antifungal, however, differences in susceptibility were observed between the different types of fungi tested. Remarkably, the growth of Pythium irregular was inhibited by up to 62 percent compared to the (untreated) control treatment when both the tomato extract and the hop essential oil were combined.
Before these products can be registered for use, their effects on other organisms in the greenhouse must first be understood.
Currently, the phytotoxicity of the extracts and essential oil is also tested when applied to the leaves of the crop to ensure that the health of the plant is minimally compromised while maintaining good insect control.
Slight phytotoxicity was observed with applications of 25 mg / ml of the tomato extract, with damage increasing at the doses of 50, 100 and 200 mg / ml. A modified saponin formulation can reduce phytotoxicity and increase potency and will be tested at a later date.
Future studies will evaluate the effects of these natural products on biological control agents used in greenhouse production, as well as test combinations of these products against insect pests to assess possible synergistic effects.
At a time when sustainability is more important than ever, pest control solutions with waste products offer the opportunity to close the loop and focus on a circular economy. However, the ultimate practical goal is to develop low risk biopesticides for use in greenhouse production.
This project is funded by 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 Research Technician on the University of Guelph Ridgetown campus. For more information, contact Dr. Lachance at [email protected]