Given half a chance, microscopic pathogens will eat our crops for breakfast, lunch and dinner - causing diseases which lower yields, reduce harvest quality or even contaminate the crop with harmful toxins. Short generation times mean they can adapt quickly to our defences, whilst international trade, crop monocultures, and climate change are helping them spread rapidly around the globe.
Weeds represent a growing threat to crop yields and global food security. Although the widespread use and efficacy of herbicides has meant that large yield losses from weeds have been largely avoided since the introduction of chemical weed control in the 1960s, widespread evolution of resistance to herbicides is leading to increasing yield losses from weeds in intensively managed cropping systems. Epidemics of herbicide-resistant species are now becoming increasingly common including black-grass in northwest Europe, Palmer pigweed in southern and central United States, and Wimmera ryegrass in Australia.
Insects are a huge problem for food production, either through direct feeding damage to plants or by the crops diseases they spread. But insects also play a vital role in the functioning of terrestrial ecosystems, and they are in steep decline. Balancing crop and insect protection is tricky to achieve - but mitigating against the overuse of insecticides will reverse population declines, thereby protecting the important roles that insects play in our farmed landscape, such as pollination, decomposition, and pest regulation.
STRAIGHT FROM THE EXPERTS
We need to protect crops and the environment
“It is estimated that within the current cropping systems, 50% of production worldwide would be lost without the use of pesticides. However, that doesn’t mean that we shouldn’t be developing better and more sustainable control of pests, weeds and diseases that doesn’t rely on conventional pesticides.
“What we need is a ‘crop and environment protection’ strategy that considers the effects of pest control alongside protecting non-targets. To develop such systems needs basic discovery science looking at combining good agronomy, healthy soils to produce resilient crops, stable host plant resistance and better integrated pest management using field margins/inter cropping, biopesticides, and naturally occurring insect and plant signalling chemicals.
“There is still a place for the judicious use of chemistry to firefight outbreaks of pests, diseases and weeds when other measures have failed or there are new, unexpected threats to our crops. For this we need selective compounds that affect only the target organisms. We also need to work closely with the stakeholders who can help us deliver such systems, such as agrochemical companies, agronomists and farmers.”
Efforts are ongoing to improve plants’ abilities to fight diseases
“If we stopped using fungicides to control pathogens, all crop yields would immediately drop by 15-25% and for some farmers in high pressure disease situations, they’d have to give up on some crops altogether.
“An increasing number of fungicides have been banned, and commercial plant breeders have increased efforts to develop new crop cultivars with broad spectrum resistance to multiple fungi types. This breeding effort is ongoing but is slow - and often these new varieties are lower yielding because these plants use some of their energies to protect themselves – but things will get better.
“Several new and faster ways are being pursued to protect crop plants. These include the identification and elimination of features of the host that make them susceptible to disease, such as certain ‘susceptibility’ genes; ‘hybrid crops’ that have been crossed with other varieties or sometimes wild relatives to gain more disease resistance genes; and the use of nanoparticles coated with RNA molecules that directly target and silence genes in the pathogen needed to cause disease.
“These new ways will be in use on farm within the next 10 years.”
Crops lost to disease lead to wasted fertiliser, water, and land
“Although there is a desire to reduce chemical applications, fungicides reduce the carbon footprint of crop production because other inputs such as fertilisers, aren’t wasted when crops are lost. There is something like a 12% reduction in net GHG-emissions per tonne of food produced by using fungicides compared to production without fungicides because of the additional land needed to make up the shortfall.
“Improved surveillance, monitoring and forecasting of plant pathogens and pests can help to reduce unnecessary applications of crop protection products. We’re currently improving detection of airborne spores that cause the most important plant diseases to improve timing of when the products are applied. Our spore detection work is developing automated spore traps that text the grower to alert them if key pathogens are present - allowing them to apply chemicals only when needed.”
We need to monitor crops for fungi – but also fungicide resistance
“Currently fungicides play an essential role in protecting crop yields, but many disease-causing fungi have developed complete or partial resistance to multiple types of fungicide. Moreover, increased regulations are reducing the chemical options available to growers, and insufficient chemistry is coming through the industrial pipeline to replace those that are lost. Although alternative approaches will be deployed in coming years (such as RNAi, biological control), fungicides will continue to have a role to play in crop protection as part of integrated pest management strategies.
“Looking forward, ongoing resistance monitoring in pathogen populations, combined with deployment of appropriate resistance management strategies, will be critical to prolong the lifespan of fungicides and protect crop yields. New technologies will enable ‘smarter’ and greener crop protection, with real-time, in-field detection of multiple fungal pathogens, and quantification of fungicide resistance in pathogen populations.”
Genome editing has the potential to enhance disease resistance in crops
“Genome editing clearly has the potential to reduce the use of fungicides by accelerating development of cultivars, which are resistant to certain groups of fungal pathogens. The technology is a versatile tool for improving crop traits, including disease resistance and herbicide tolerance. Since, in some cases, plant susceptibility to pathogens is conferred by the presence of susceptibility genes, genome editing has improved disease resistance by knocking them out – as seen with the powdery mildew disease in wheat and tomato.”
Pesticide-free is unlikely - but we can certainly reduce it
“There is a Europe wide effort to reduce pesticide inputs while maintaining yields. This includes evaluating weed management approaches that use non-chemical approaches; making software and apps that facilitate reduced pesticide use more readily available and usable; and quantifying the contribution of biodiversity to control crop pests.
“The research is finding that it is usually the case that a completely pesticide-free approach will incur a yield penalty but is also demonstrating the potential of promising non-chemical alternatives to reduce pesticide inputs. These include ecological approaches to regulating weed populations, and the contribution of a diversity of natural enemies to controlling crop pests.”
We need to protect crops and the environment
“Because of the effectiveness of herbicides at supressing weeds, they’ve become a mainstay of conventional farming - and simply dropping all herbicides from the equation would very likely lead to reduced yields. Unfortunately, we also now know that weeds can rapidly adapt to repeated herbicide use. Over 260 species worldwide have evolved some form of herbicide resistance, making weed control strategies which are reliant on herbicide alone less sustainable in the long term.
“Thankfully, the potential of other non-chemical and ecological weed management strategies has now been highlighted, and technological advancements in weed detection and suppression can also play a role. Research now suggests that by combining herbicide use with a diversity of non-chemical approaches and using technology to target weed plants more effectively in future, it may be possible to reduce total herbicide use and selection for resistance whilst maintaining effective weed control.”
Weed genomics just the germ of an idea
“There have been relatively few times where molecular biology and genomics techniques have been applied to weed sciences compared to model or crop plants. There are a handful of studies published across a variety of species, and although the number is increasing, only about five weed species genomes are publicly available. This is very different from what is happening in crops where many genomes are available, myriad molecular techniques are routine, and numerous different groups are using these to generate knowledge that leads to improved crops.
“Instead, Weed Science explores more than 260 species that have recorded herbicide resistances, for which, we have just a fraction of the genomic data, limited optimized molecular techniques, and fewer shared resources. Looking at the impact the genomics revolution has had on crop science, we can feel confident that increasing access to weed genomics and optimising and applying molecular techniques will make a difference to how we understand and therefore control weeds.”
Persistent use of insecticides is not the answer
“The long-term solution is smart agriculture because we need to protect both nature and the people working in agriculture. We often forget that nature is joined up, linked by many complex relationships that we still don’t understand fully. Fiddle with one bit, and that effect may ripple over and cause an unexpected outcome in another. Likewise, it’s not always widely acknowledged that growers are exposed to huge financial risk – they are after all a business and will only grow crops if they can see a profit.
What does smart agriculture look like? Well, it's not one thing but a composite of many things - although it’s certainly not the persistent use of insecticides. We need consumers to get past an aversion to ‘wonky fruit and veg’ and communicate that even blemished vegetables and fruit are still good to eat and are a product of a healthy environment. We also need to support science that seeks to help growers make important financial and environmental decisions. For example, the industry should adopt forecasting tools to inform when and if to use insecticides, catalyse crop breeding to build resistance to pests, and deliver innovative soil management science to support the system in which insects need to thrive."
A better understanding of pests will help alternative control development
“For the foreseeable future, chemical interventions will be required to protect food production yields from insect pests. However, it is certainly possible to better manage the use of traditional pesticides more effectively and move away from current prophylactic application methods through integrated pest management systems.
“This approach combines several different techniques to help control crop pests including, effective pest monitoring systems that allow for timely application of control measures only when pests are above a critical threshold; biological control methods (such as natural enemy recruitment); and new ecological control methods such as using pest insect pheromones to bait insect traps or using large amount of pheromone to disrupt their mating.
“Traditional and new, more selective chemical pesticides still have a place but only when all other control methods have failed. Development of alternative control methods requires the fundamental basics of the insect-crop system to be better understood.”
Whether driven by politicians, consumers, or pests’ evolving resistance, it’s clear our approach to crop protection needs to change. There is no silver bullet, but a range of methods that when used together, could significantly reduce our pesticide use.
By utilising technology, such as fungal spore monitors or real-time insect surveillance data, farmers could limit spraying to only when it is needed. The development of crops better able to withstand pests and diseases will also help, as will a better understanding of how we can harness nature to control outbreaks of pests and weeds. More diverse rotations to lengthen the amount of time between the same crop, combined with improved soil health, will be needed to reduce land used for food production and the carbon footprint of farming, while helping maintain a secure food supply.