By Joseph D. Levitsky
Controlling pests protected within the confines of the soil has always proven to be a difficult challenge faced by farmers. These pests, unchallenged, grow in numbers year after year, damaging large portions of crops beyond the point of saleability or profitability. Currently, the popular solution is the use of a broad-spectrum soil-fumigant; moreover, this gas does not discriminate between organisms, and provides an effective kill to anything within its treatment area.
Short term, fumigation is a reasonable solution. Planting a crop in a sterile field provides ease of mind to farm owners, and its one-time application prior to planting can be initially economical. But what happens when the farmer plants a perennial crop, one that remains in the same location for multiple years? When fumigation is no longer an option, as it poses a risk of killing the entire crop along with the target pests? The short answer is little can be done.
Tom Baumann, associate professor in the Agriculture Department at UFV, shares that perennial crops—particularly raspberries in the Fraser Valley—are declining in productivity due to increasing populations of soil-borne pests such as nematodes and other pathogens.
Pest management in perennial crops is one challenge, but management in annual crops like carrots and potatoes also has its challenges. Yearly crops allow farmers the opportunity to fumigate between every crop cycle. While, in theory, this should kill any established populations within the field, the truth is that it contributes to the occurrence of pest populations that are resistant to fumigation altogether, creating a foreseeable out-of-hand infestation or infection.
Well, what is the solution?
Organic farmers, who don’t use chemical control-agents like fumigants, have created a need for the development of other management strategies. The use of biological organisms to control a target pest is not a new concept. For example, farmers have been maintaining populations of feral cats as biocontrol agents to control mice populations in barns for many years. This method of pest control, applied to target pests within the soil, is no different. Additionally, the formation of resistance cannot adapt to predation, leading to a longer-lasting and more trusted method of control.
Unfortunately, unlike the tried and tested use of cats for mouse control, the use of other particular organisms is untested and effects are unknown. A combination of a rising need for pest control solutions and an apparent gap in knowledge in this field is driving research in soil-borne pest management.
Two particular soil-borne pests which cause economic loss across various agricultural crops are referred to as wireworm (the larval stage of the common click beetle) and Fusarium Rot (a disease caused by the Fusarium oxysporum pathogen). These two pests are entirely different in their biology, but share similarities in their tenacity in crop destruction and persistent presence for years within the soil.
Wireworms are generalists that feed on the roots on many root crops, making control by crop rotation redundant. While each Fusarium strain is specific to each crop, it can remain dormant in the soil for over a decade.
Benefits of biocontrol
Establishing a community of organisms that actively hunt the target pest has the capacity to provide control over the entire lifespan of the crop. Unlike fumigation, the target pest will never be completely eliminated from the field; however, the pest numbers should be kept perpetually in check. Without chemical intervention, the crop also has the potential to benefit from the presence of other beneficial organisms. For example, a fungus called rhizobium forms symbiotic relationships with legume crops; the rhizobium provides nitrogen taken from the atmosphere to the crop, while the crop provides simple sugars to the rhizobium. The occurrences of beneficial organisms only contribute to increased yield potential.
Promising developments against fusarium root rot
The impact of soil-borne fungi can be detrimental to a farmer’s field, not to mention any neighbouring fields. Fusarium has the ability to remain in a dormant state within soil until its particular food source—our food—is reintroduced into the field. This dormant form can be transported by soil attached to farmer’s boots and equipment tires to other fields where it awaits its target. Generally speaking, the occurrence of this pathogen in any farmer’s field is more or less inevitable.
Recent studies have found promising results with the use of nematodes as predators against the fungus that causes Fusarium rot; although, further research on how these organisms interact in actual field conditions has yet to be accomplished. The sheer diversity of nematodes in the soil results in a wide range of species that are specialized to different resources—mainly other organisms within the soil. It is reasonable to speculate that that there are nematodes specialized to target each agricultural pest; however, identifying the species and determining their relative efficacy requires much research.
In addition to nematodes, other research suggests certain yeast species isolated in Egypt have the capacity to control the Fusarium causing fungus with up to 60% inhibition. While this is not necessarily a curative control method, effective control could be maintained in combination with other biocontrol agents.
Promising developments against wireworm
Wireworm, being a generalist insect, feed on the roots of grasses and corn, as well as any other energy-storing root crop like potatoes, rutabagas, carrots, turnips, beets, or garlic —to name a few. Being a generalist allows this pest to thrive in any crop planted in the soil, making infested acres potentially useless.
Research conducted in 2009 tested the use of nematodes and two strains of fungi against populations of wireworm. While the use of nematodes only provided 35% control in field conditions, a combination between these nematodes and other biocontrol agents have the potential to provide acceptable control. On the other hand, the most promising results for the control of wireworm involve two fungal strains (Metarhizium anisopilae V1002 and LRC181A) which provided 90 to 100% control over wireworm populations.
Farming, by nature, is a high risk business endeavour; it involves many high-cost inputs to a volatile product that is susceptible to adverse weather, chemical damage, disease, pest damage, and market deflation, among other common business risks. A farmer’s willingness to adopt new methodology, that may or may not work, is nothing short of tenuous.
The largest problem is that farms willing to adopt the use of biocontrol agents need to adapt their current pest management strategies to work with biocontrol agents. While many other pests, such as aphids, are easy to control with chemical applications, the simple presence of pesticides in the environment has the capacity to kill any biocontrol agents. Unlike adopting the use of a new chemical, adopting the use of biocontrol agents ultimately restricts the use of many other helpful chemicals.
A seemingly simple solution would be to convert all pest management practices to biocontrol agents; however, the lack of research and development within this technology leaves a limited selection of biocontrol agents.
One might respond with the solution to simply increase research in this area, but there lies the next hurdle that is Canada’s Pest Management Regulatory Agency (PMRA). This lengthy 12 section (excluding sub-sections) process is intended to fully understand the implications and effects that a particular product (mainly chemical) will have on the environment, and has the potential to last several years before approval.
The future of biocontrol agents
Further development of the biocontrol agents discussed above should not be abandoned. Even though efficacy is too low in providing a curative fix, their use in combination with other biocontrol agents and cultural prevention techniques could provide effective control for farmers. A community of predatory organisms will provide longer lasting control over soil-borne pests than any pesticide or fumigation.
As soil-borne pests gain resistance to the limited chemicals available for control, a greater emphasis will be placed on biocontrol agents. The unique needs of each farm will require unique combinations of biocontrol agents for a complete pest control program. Until a wider range of biocontrol agents are available for combined use and synergy, this method of control is just as limiting as fumigation. To expedite the increase of available biocontrol agents, local farmers need to express their individual interests and their increasing need for these products to create a realized demand.
[infobox title=’Joseph Levitsky’]Joey Levitsky is in his third year of full-time Bachelor of Agriculture studies at the University of the Fraser Valley with a focus on practical scientific applications in the agricultural industry. He combines this knowledge and experience with opportunities to work within the industry, observing farming practices, identifying and quantifying damages, and predicting resulting yields at his part-time job with Expert Agriculture Team Ltd.[/infobox]