Cover Crops More Effective Than Insecticides for Managing Pests
Promoting early-season plant cover, primarily through the use of cover crops, can be more effective at reducing pest density and crop damage than insecticide applications, according to a Penn State-led team of researchers.
In a newly published study, the researchers suggest that the best pest management outcomes may occur when growers encourage biological control in the form of pests’ natural enemies by planting cover crops and avoiding broad-spectrum insecticides as much as possible.
The use of cover crops and other conservation-agriculture practices can help reduce erosion and nutrient loss, enhance soil health, and improve pest management, noted study co-author John Tooker, professor of entomology in Penn State. Although the adoption of such methods has increased, he said, the use of pesticides continues to grow in the United States and globally, potentially killing nontarget, beneficial species and reversing pest-management gains from the use of conservation-agriculture tactics.
“Plant cover, such as cover crops, can provide habitat for populations of natural enemies of pests,” Tooker said. “Winter cover crops, for example, can harbor predator populations outside the growing season of the cash crop. Once the cover crop is killed to allow the growth of the cash crop, cover crop residues remain on the soil during the growing season and enhance habitat for predators.
“Studies have found that cover crops reduce insect pest outbreaks by increasing predator abundance, but to retain these benefits, it’s critical to protect these predatory species,” he said.
The goal of this study was to investigate how conservation-agriculture practices — cover crops, no-till planting and crop rotations — interact with two pest-management strategies that employ insecticides. These strategies are preventive pest management, in which growers plant seeds treated with systemic insecticide for the control of early-season pests, and integrated pest management, or IPM, an approach that involves scouting for pests and using insecticides only when pest numbers exceed economic thresholds, and then only when nonchemical tactics are ineffective.
The researchers set out to examine these scenarios by establishing two experimental no-till fields at Penn State’s Russell E. Larson Agricultural Research Center to test the effects of pest management and planting small-grain cover crops over three years in soy-corn-soy and corn-soy-corn rotations.
The team divided each field into plots, with six treatments each replicated six times in each field over three years. While the crop species changed annually with the rotation, each plot received the same treatment each year.
For the IPM strategy, researchers scouted the IPM plots for insect pests and compared pest populations to economic thresholds to determine whether insecticide applications were needed. They used an insecticide — a single, in-furrow application of a granular pyrethroid — only in the second year of the study.
The researchers, who recently reported their results in Ecological Applications, found that using any insecticide provided some small reduction to plant damage in soybean, but no yield benefit. The findings suggested that in corn, vegetative cover early in the season was key for reducing pest density and damage.
An unexpected result, the team said, was that the IPM strategy, which required just one insecticide application, was more disruptive to the predator community than preventive pest management, likely because the applied pyrethroid was more toxic to a wider range of arthropods than neonicotinoid seed coatings.
“With the single use of insecticide in the IPM treatment, nontarget effects persisted more than a year after application, without reducing plant damage or density of white grubs, the targeted pest,” Rowen said. “This pyrethroid also indirectly decreased soybean yield in IPM plots more than a year later, perhaps because of having fewer predators present to protect plants.”
This finding highlights the importance of choosing the most selective insecticide possible when chemical control is justified within an IPM strategy, Tooker explained.
The researchers concluded that planting cover crops and fostering natural-enemy populations protected corn and soy from damage and that promoting early season cover was more effective at reducing pest density and damage than either intervention-based strategy.
“But because cover crops can also leave cash crops vulnerable to some sporadic pest species, growers should be careful to select the best cover crop species for each situation and to scout regularly for early-season pests,” Rowen said. “In addition, maximizing the benefits of cover crops for biological control requires sparing use of insecticides, because preventive use of selective insecticides and reactive use of broad-spectrum insecticides both can reduce predator activity without guaranteeing pest control or greater crop yields.”
| How does this knowledge affect growers? From Dr. Jonathan Lundgren: Despite good intentions, integrated pest management was doomed to fail from its inception. Its inherent problem is that insect pests are not an entomology problem, but integrated pest management treats them as though they are. Prior to the 1940s, insect pests strongly influenced human culture. They directed where we lived on the planet (disease transmission), what we ate and when we decided to be outside, and they scurried their way into our vernacular (e.g., “bugs in the system,” “a lousy fellow”). Synthetic pesticides changed all of that. The discovery that organochlorines killed insects led to the rise of DDT and its kin, and we used it indiscriminately across the land and water. Insecticides were applied as an insurance policy against the possibility of pests, and corporations fed this misperception with great gain. Insect pests became resistant to the pesticides, necessitating more chemistries to be applied. To reduce the rising use of insecticides and increase their longevity, the Integrated Control Concept was coined (in 1959 by Smith et al.). It established the concept of economic thresholds — insect pests only need to be treated when they exceed a certain population level. And this theoretically should have reduced insecticide inputs. Fifty years later, arguably, the verdict is in. IPM did not deliver on its promises. We now apply pesticides to more acreage than we ever have. Doses may be a little lower, but their impact is far greater because many of the chemistries are directly and indirectly more toxic to life than even the early organochlorines. They are marketed as things like genetically modified crops and seed treatments. These days, a big part of managing pests is all “in the bag”; insecticides are again used as an insurance policy against insects becoming a problem. Wildlife is declining; insects around the world are in decline; human health is deteriorating rapidly. A central problem with IPM as it is practiced is that it assumes that pests are inevitable. Farmers from around the world have taught me, though, that pests are only a problem when your system doesn’t have enough diversity in it and when you have too much uniform disturbance. Insect pests aren’t an entomology problem. Insect pests are a soil problem. They are a problem of a system devoid of life. But most of all, insect pests are a cultural problem. The Penn State study reveals that cover crops were more effective than IPM and insecticidal seed treatments in managing pests using biological control on an experiment farm. This research is commendable; it adds fuel to the fire that cover crops are a viable tool for managing pests in this region. I think that an even more valuable contribution is that this study examines pest management on a bit more of a systems level. Cover crops and the biological control it supports are identified as the mechanisms behind why the cover crop system functions relative to the PPM and IPM systems. Our experience at Ecdysis Foundation is that this is only part of the story. Cover crops and biological control only work on farms when they are embedded in an agro-ecosystem that fosters soil health and life. Indeed, they are a part of that system. But if we only focus on these two elements of the system, we will slip into the same hole we did with IPM. The cover crops, along with no-till and abandonment of pesticides, in the system developed for the study do a lot more than increase the number of predators on a farm. Covers change the microclimate, making it more difficult for pests to grow. They increase the number of benign herbivores, potentially increasing competition with pests. They alter the physiology of the crop plant, potentially making the crop more resilient to pests. They alter the microbial community, potentially leading to altered symbioses that keep herbivores in check. The science is clear that plant diversity, cover and minimal uniform disturbance to the soil are inherent in pest suppression. We make our pest problems when we sterilize our farms beyond recognition as ecosystems. We know regenerative food systems work, but we can’t always know all of the mechanisms for why. In sum, the natural world is complex beyond our ability to understand it. Science is slowly catching up to the farmers who have created viable systems that are devoid of pests. Until then, science needs to take a back seat to faith. |
Study Finds Fungicides on Apples, Other Fruits Can Host Drug-Resistant Bugs
Fungicide treatments on apples and other fruits to prevent spoilage and extend shelf life may help host and boost the transmission of pathogenic yeasts that are multi-drug resistant, warns an international team of researchers.
According to mycologist Anuradha Chowdhary from the University of Delhi, studies so far have examined the effect of fungicides on the human pathogen Aspergillus fumigatus. But the new work, published in the journal mBio, focuses on drug-resistant strains of Candida auris, a pathogenic yeast that spreads quickly in hospitals and has been isolated from nature.
Fungicides used in agriculture may inadvertently select the drug-resistant fungi, Chowdhary said.
The team screened the surfaces of fruits for pathogenic C. auris and other yeasts. The fruits were collected in 2020 and 2021 from areas of northern India and included 62 apples — 20 picked in orchards and 42 purchased from a market in Delhi.
Each fruit species hosted at least one type of yeast. The scientists found drug-resistant strains of C. auris on a total of eight apples (13 percent) and used whole-genome sequencing to identify 16 distinct colonies. The apples included five Red Delicious and three Royal Gala varieties. All 8 of those apples had been stored before purchase, and none of the freshly picked apples hosted C. auris. The group found other Candida strains on the packed apples.
C. auris is resistant to many drugs. It was first identified in 2009 in Japan, and since then it has emerged in or spread to all inhabited continents. Researchers have been investigating how the pathogen originates and spreads. The new findings suggest the apples could be a selective force for the pathogen and could help it to spread.
Chowdhary said the new study shows how the environment, animals and humans are all connected.
| How can this information aid growers? From Kathleen DiChiara: Before we become discouraged by the new findings, let’s first consider the role that our eating habits may be playing in creating the next superbug. Our global food system has changed the way we consume food. In fact, most people expect to see their favorite fruits and vegetables at the supermarket all year — even when they’re not in season locally. Harvest season for apples in the U.S. varies depending on the variety and the state, but it generally falls somewhere between early August and mid-November. Only about 5 percent of apples consumed in the U.S. are imported, according to the U.S. Apple Association. So, if you’re biting into an apple in April, it was likely harvested months ago. Bacterial and fungal communities on apples are inevitable — after all, fruits have their own ecosystems. However, the type of growth that apples host is highly dependent on the number of inputs between harvest and consumption. In fact, microbiome analysis of fresh apples in the present study showed negative results for C. auris. The research suggests that the origin of C. auris on the surface of stored apples is most likely from contamination of apples by human hands that were colonized with C. auris during postharvest and storage and through the distribution chain. An apple’s surface has a natural protective wax to reduce water loss and prevent pathogenic attacks. However, to increase shelf life of stored apples, common practices include precooling, washing, sanitizing and then applying a thin layer of edible wax consisting of esters of a higher fatty acid with monohydric alcohols, hydrocarbons and free fatty acids, to replace what was stripped away. This allows apples to be stored for 6 to 12 months at low temperatures before distribution — a shocking fact to many people. Once the apples are prepared for transport, they are often treated with a fungicide to prevent spoilage, which may help select and boost the transmission of pathogenic yeasts that are multi-drug resistant. It seems that once we implement post-harvest practices to extend shelf life, we amplify the growth of C. auris, which dominates commensal strains and other yeasts. So, before we chase down stronger antifungals medications or more fungicides, perhaps we should reconsider whether all our efforts to make fresh food “shelf-stable” are worth it. Perhaps, eating local, seasonal food in rhythm with Mother Nature would be a better public health measure. |
Language of Fungi Derived from their Electrical Spiking Activity
Researchers at the University of the West of England’s Unconventional Computing Laboratory have discovered that fungi “exhibit oscillations of extracellular electrical potential” — electrical communication — that is similar to human speech. The results were published in the journal Royal Society of Open Science.
The team studied four different species of fungi (ghost fungi, Enoki, split gill and caterpillar) and measured their electrical signals via microelectrodes inserted into the organisms’ mycelia — the microscopic roots of a fungus. They detected spikes of electrical signals that are often clustered into “trains of activity.” These trains are comparable in distribution and fungal word length to human languages. The average train was about six spikes, which is comparable to the number of words in an average human sentence.
Several of the species of fungi appear to exhibit more complex communication than others, and patterns of communication change in response to external electrical, optical, chemical and physical stimulation.
| How does this affect farmers? From Harriet Mella: Brain death means the cessation of electrical spikes. So our functions of life and our intelligence are associated with patterns of spikes — not just random activity. It is well known that fungal mycelia generate electrical spikes — evidence of bread mold being electric was published as early as 1976. So why does a publication that claims that fungi have an electrical vocabulary of 50-word patterns cause such a stir today? Is it new knowledge that organisms communicate? No. Is it esoteric that organisms communicate? No. Is it legitimate to apply pattern recognition algorithms to fungal spikes? Yes. It is beginning to become common knowledge that the vegetation and its belowground partners are one communicative network. What is causing controversy is the idea of intelligence being attributed to the targeted, fast communication. The electrical language seems to be a universal language, just as universal chemical signals may be — ageing bacterial biofilms, such as those associated to roots, attract other species with electrical oscillations. An older study shows that a fungus gets electrically excited when finding food. What we do not know — and this is where the opinions diverge — is if the excitement is perceived as such by the fungus and if we are looking at information shared on purpose — or if the spikes are simply byproducts of growth processes. Plants do react with and to electrical signals, so it is a fair possibility that they coordinate their behavior with fungi and bacterial biofilms through electrical and chemical signals in one integrated network. While we are now confronted with the question of how much intelligence to attribute to our soil, it is a safe bet that agricultural techniques that deprive a soil of its “nervous system” — the extended network of fungal hyphae interlinking microbes — causes the loss of a good part of a soil‘s functionality. Has anyone ever looked at roto-tillage as a soil-dementing disease? Pathogenic fungi spring back from soil disruption much better than the “beneficial” mycorrhizal network. Maybe in the long run this research about fungal communication will bring us back to a more literal understanding of soil as nature’s body. |
