Time running out to prepare for wave of new plant diseases
© Blackthorn Arable and Tomasz/Adobe Stock Climate change is putting arable crops at greater risk from attack by pests and diseases never before seen on UK shores.
According to a scientific review by the Food and Agriculture Organisation (FAO), a single, unusually warm winter may be enough to help an invasive pest establish in temperate regions such as the UK.
While half of all emerging plant pests and diseases are spread by global travel and trade, Defra says weather is the second most important factor.
The biogeography of the British Isles means that many airborne pests and pathogens can naturally traverse the English Channel and spread from continental Europe.
Agricultural crops, horticulture, flowers, and fruits and vegetables are big business in the UK – they are estimated to contribute £4.1bn to the economy every year.
But in the past 25 years, diseases such as cercospora in sugar beet and ramularia leaf spot in barley have taken hold in the UK, and small outbreaks of wheat stem rust have appeared sporadically, threatening that trade and food security.
Outbreaks warning
James Brown, plant pathology research group leader at the John Innes Centre in Norfolk, says although recent outbreaks of stem rust have not been large enough to cause economic damage, it is a warning of things to come.
New strains of wheat yellow rust, which attacked some previously resistant UK varieties, emerged in 2011.
And barley yellow dwarf virus, a virus transmitted by aphids and previously well controlled by insecticides, is a cause for concern because neonicotinoids can no longer be used as a treatment.
In horticulture, the tomato brown rugose fruit virus, which affects mainly tomato and sweet pepper plants, was detected in the UK in June 2019 – five years after the first cases emerged in Israel, causing significant economic losses for growers.
Number of potential pests
There are a vast number of potential plant pests and pathogens that could take hold in the UK; the UK Plant Health Risk Register has identified more than 700 for either further research or as a potential threat to the UK.
And there are 165 pests that threaten UK potato cultivation alone, including potato flea beetles, which can cause a major impact on the crop’s commercial value. In the past, it has been intercepted on ware potatoes at the UK border.
Prof Brown says identifying which countries diseases emerge from is not straightforward, but some of the new strains of yellow rust are known to have come here from east Asia.
“Human movement is the biggest risk of introducing rust, with spores coming into the UK on clothes and footwear,” he says.
Climate change
Climate change is one reason why wheat stem rust has taken hold in the UK, and it is likely to set a precedent.
“Modelling has shown that, over the next 50 years, warmer summers could see diseases associated with hot climates becoming more of a problem in the UK,” says Prof Brown.
One of the biggest consequences for crop production that he sees from climate change is the unpredictability it brings to weather patterns.
“What that unpredictability means for plant diseases is less understood, but we are probably going to get more outbreaks in crops,” he warns.
Is enough being done to prevent diseases emerging?
One of the principal actions to ward off the emergence, or re-emergence, of plant disease is effective breeding.
For example, breeding for resistance has meant better than anticipated control of yellow rust in old varieties, as well as new ones.
In the case of Septoria nodorum, this once prevalent disease, which mainly infects wheat, has virtually disappeared from the UK by breeding for durable resistance.
Many farmers do grow more resistant varieties, but some don’t, and these susceptible varieties play a disproportionate role in spreading disease.
With Septoria tritici, if all farmers chose to grow varieties with at least moderate resistance, there would be less of a problem, says James Brown of the John Innes Centre.
But there are multiple factors why farmers choose a variety – quality, maturity date, standing power, and resistance to other pests and diseases, to name some of them.
Resistant varieties needed
Hasty decisions to withdraw broad-spectrum fungicides and insecticides, including neonicotinoids, have not allowed plant breeders time to breed varieties resistant to some diseases.
“When new diseases comes along, we don’t have resistant varieties – they need to be bred and that is a long process,” Prof Brown points out.
In the case of Septoria tritici, which emerged in the UK as a major problem in the 1970s, it took 20 years before breeders started to release resistant varieties, and another 20 years to get to the point where those varieties could compete with established modern varieties.
“The 2018 neonicotinoids ban was introduced quickly, but it takes nine years to release new varieties of winter cereals, and five years for spring varieties,” he says.
“We have to produce varieties that are not just resistant to one pest or disease, but varieties with at least moderate resistance to all pests or disease. Just focusing on one problem is not the solution.”
Crop management and production will also have a greater role to play in disease control, with the withdrawal of neonicotinoids from general use.
Strategic approach to disease control
The global database of the European and Mediterranean Plant Protection Organisation lists more than 90,000 pests and diseases of interest to plant protection, agriculture, and forestry.
The database spans insects, bacteria, fungi, viruses, and nematodes, yet there are a significant number of species which are not included.
So, what measures are in place in the UK to protect crops and plants from these?
According to the Animal and Plant Health Agency (Apha), there are robust systems to monitor emerging diseases and to identify risks, including the UK Plant Biosecurity Strategy.
This policy, a partnership between the UK, Scottish and Welsh governments and the Forestry Commission, was agreed in January 2023 to co-ordinate the approach of countries to plant biosecurity over the next five years.
It is the second plant biosecurity strategy for GB – the first was in 2014 in response to the first cases of ash dieback being identified.
The pathogen arrived here naturally as wind-blown spores and through the importation of infected ash trees.
Defra says its latest strategy will create a new biosecure plant supply chain to safeguard food security and help mitigate the effects of climate change.
As part of that, Apha’s Internet Trading Unit will be expanded to increase monitoring of online retailers and social media sites for the trade of high-risk plant products.
Certification
Certifying seed is another way to reduce pests and diseases; all seed bought and sold in the UK must be certified and wheat quality must meet EU minimum standards.
But if new pests or diseases do infiltrate these controls, with fewer treatment options now on the market for growers of all crops, managing them will be difficult.
“Once a new pathogen or pest is here, it is here – we need to learn how to control it once it has arrived,” says Prof Brown.
“While breeding for durable resistance has been shown to be effective, for instance, in wheat mildew and barley brown rust, time won’t be on our side.”