Digging into the Data: Biopesticides for Grape Disease Control
With data contributions from Wayne Wilcox
“Biopesticides” are moving into the mainstream. While earlier versions gained a reputation for only modest efficacy in comparison with conventional synthetic fungicides, new products are proliferating – and offer comparable performance that sometimes rivals the ‘gold standards’ that growers rely upon. In disease management spray trials at Cornell, we have been evaluating biopesticides for the past nine years. So, how well do they work? Where do they fit into a disease management program?
However, before we get into performance, we must first discuss the performers.
Biopesticides have fundamentally different modes of action from traditional chemistries. Understanding this difference is key to understanding how biopesticides can fit into an integrated grape disease management program. This article will introduce the different types of biopesticides, discuss considerations for their use, and delve into the Cornell Grape Pathology archives to see how biopesticides have performed over the years for grape disease control.
What’s a biopesticide?
Biopesticides are products derived from such natural materials as animals, plants, bacteria, and certain minerals. For example, kitchen products such as canola oil and baking soda have antimicrobial applications and are considered biopesticides. Because it is often difficult to determine whether a substance meets the criteria for classification as a biopesticides, the Environmental Protection Agency (EPA) has a special committee dedicated to making these decisions.
Biopesticides are the fastest growing market sector of pesticides despite only representing 5% of the global pesticide market. As of August 31, 2020 the EPA has 390 biopesticide active ingredients registered. In the 5-year period between 2015 to 2020, almost 100 new biopesticide active ingredients were registered with the EPA.
Since biopesticides tend to pose fewer risks than conventional pesticides, EPA generally requires much less data to register a biopesticide than to register a conventional pesticide. In fact, new biopesticides are often registered in less than a year, compared with an average of more than three years for conventional pesticides.
How do biopesticides work?
Just like how we separate traditional chemistries by their modes of actions, there are different types of biopesticides. The EPA defines three types of biopesticides, however these can be broken down further.
Biochemical pesticides. A biochemical pesticide is a naturally occurring substance that controls pests and/or pathogens by non-toxic mechanisms. Biochemical pesticides can have plant, animal, microbial, or mineral origins. In terms of grape disease control, the most common biochemical pesticides are plant extracts and microbial extracts.
Plant Extracts. Before people came along, plants had to save themselves from pathogen and pest threats. You’re likely more familiar with these sorts of compounds than you realize, as many naturally occurring compounds, such as caffeine and nicotine, have been harnessed for eons for non-agricultural, human use. An example of a plant extract biopesticide is Regalia.
Microbial extracts. Microbes have been fighting each other for far longer than they’ve been fighting plants. Microbial extracts, such as penicillin, the first antibiotic, are the foundation of much of modern human medicine. An example of a microbial extract biopesticide is Oso.
Mineral & misc. compounds. Oils and mineral compounds are considered biochemical pesticides under the EPA’s definition. This category includes a variety of commonly used pesticides including oil (JMS Stylet Oil), silicon (Sil-Matrix), copper (Cueva), phosophorus acid (Phostrol), and hydrogen peroxide (Oxidate).
Microbial pesticides. A microbial pesticide consists of a living microorganism (e.g., a bacterium, fungus, virus, or protozoan) as the active ingredient. Microbial pesticides can control many different kinds of pests and pathogens, although each separate active ingredient is relatively specific for its target. For example, there are fungi that control certain weeds and other fungi that kill specific insects.
The subcategory of biofungicides describes formulations of living organisms used to specifically control the activity of plant pathogenic fungi. The idea behind biofungicides is based upon decades of scientific study demonstrating that some beneficial microorganisms, usually isolated from soil, can hinder the activity of plant pathogens. There are four main ways that biofungicides work.
Competition. The idea behind this mechanism is that a plant pathogen can’t take hold if there isn’t any room for it grab on! These biofungicides compete with plant pathogens for nutrients, infection sites, and general space (a “niche”) without harming the plant. For example, they may colonize the entire root surface, leaving no room for a root pathogen to attack. Additionally, some biofungicide organisms can metabolize plant exudates that would normally attract plant pathogens or stimulate their growth. An example of this type of biofungicide labeled for grape disease control is Double Nickel.
Parasitism and antibiosis. These biofungicides take a more direct approach to plant disease control by harnessing microbe-microbe warfare. They directly attack, consume, or produce compounds that destroy plant pathogens. An example of this type of biofungicide labeled for grape disease control is Howler.
Defense induction. These biofungicides don’t act upon other microbes, but instead activate the plant’s own defense system so that it can better protect itself against plant pathogens. By turning on Systemic Acquired Resistance (SAR), these biofungicides improve the plant’s response to pathogen attack by priming the production of plant defense compounds at the site of active invasion as well as throughout the plant (systemically). An example of this type of biofungicide labeled for grape disease control is Lifegard.
Plant growth promotion. The biofungicides also act upon the plant, however they do not engage the plant’s defense system. They instead promote plant health and growth, thereby improving the plant’s ability to turn on its own defenses and fight off plant pathogens.
The third category of biopesticide, plant-incorporated protectants (PIPs) are uncommon in grape disease control. These are pesticidal substances that plants produce from genetic material that has been added to the plant. For example, scientists have produced maize varieties that are resistant to the European corn borer by incorporating the gene for the Bt pesticidal protein into the plant's own genetic material. Then the plant, instead of the Bt bacterium, manufactures the substance that destroys the pest. The protein and its genetic material, but not the plant itself, are regulated by EPA.
Special considerations
When considering using biopesticides, it is important to remember that they act like a lock on a door. A good lock will stop opportunistic, weak thieves, but determined, strong thieves, or thieves in sufficient numbers, can still break through with enough force. And most importantly, biopesticides can’t stop a thief that is already inside the house when the door is locked. For most effective use, a biopesticide must be in place before pathogen infection begins as their action is majorly protective. The key exception to this is Stylet Oil, which is a highly effective powdery mildew eradicant.
Biopesticides, therefore, must be reapplied frequently both to protect new growth and to ensure that effective populations of the microorganisms are present in the case of live microbe biofungicides. Additionally, because some biofungicides consist of living organisms, they often have different storage, shelf life, and handling requirements than conventional fungicides.
How do the different types of biopesticides perform for grape disease control?
Over the years, Cornell Grape Pathology, under both its current and former captains Gold and Wilcox, has evaluated a number of different types of biopesticides in our seasonal spray trials. While there’s many ways we could delve into the data, we sought to summarize our findings simply to provide general insights into how biopesticides perform for grape downy and powdery mildew control. The graphs and table that follow below present average percent incidence control across all years studied. Percent (%) control compares treatment performance to the total amount of disease in the untreated control in a given year. For both powdery and downy mildew, we evaluated percent control on leaves and on grape clusters separately.
