A sugar beet disease in Germany is making virus yellows the forgotten challenge. CPM reports from the recent IIRB Congress in Cambridge.
“We need to find solutions quickly, otherwise we will lose sugar beet in our rotations.” ACHIM JESSER
By Mike Abram
Virus yellows might be taking much of the sugar beet research focus in the UK, but in Germany and other parts of Europe, another challenge is equally, if not more feared.
Syndrome des basses richesses (SBR) and rubbery taproot disease (RTD) (see box) have some similarities to virus yellows, in that the pathogens are vectored by an insect, and, in the case of SBR, cause yellowing of sugar beet leaves.
But rather than being a virus, SBR is caused by bacteria transmitted by planthoppers. First recorded in Burgundy in France in 1991, it’s now Germany, Switzerland and Austria bearing the main brunt of infections.
Symptoms show up in late summer as yellowing and chlorosis of older leaves, lance-shaped or asymmetrical new leaves, with necrosis of vascular root bundles, which presents as brown rings in the cross-section a root. The roots don’t rot and remain processable, but with losses of up to 5% sugar content and 25% root yield.
PATHOGEN COMPLEX
Like virus yellows, SBR is a complex of pathogens, with the proteobacterium Candidatus Arsenophonus phytopathogenicus (ARSEPH) implicated, while the ‘A’ and ‘P’ strains of the stolbur phytoplasma Candidatus Phytoplasma solani (PHYPSO) can also be present.
ARSEPH was the classic main SBR pathogen in most countries, but in Germany the ‘P’ strain of the phytoplasma is now dominant. Where both or even all three are present together, which has been found in parts of Austria, the impact on crops is usually more severe.
A similar complicated picture occurs with the cixiid planthopper vector. At least three types have been shown to carry the pathogens. Pentastiridius leporinus is more common in western and central Europe, driving the classic ARSEPH bacterial infections in much of Germany, but also transmitting the stolbur ‘P’ strain phytoplasma in eastern Germany.
GENERALIST VECTORS
In Austria and further southeast in Europe, the principal vector of the ‘P’ strain is a reptalus species, but again it can transmit either pathogen type.
Both are generalists rather than specific to sugar beet. DNA sequencing of Pentastiridius leporinus by German researcher Omid Eini at the Institute of Sugar Beet Research (IfZ) found DNA from up to 32 plant species, including weed species such as nettles, bindweed, meadowgrasses and cocksfoot.
With no direct cure for infected beet plants – the pathogens are parasites that live and feed in the plant’s phloem carrying sugars from leaves to roots, and therefore impossible to hit with a spray.
A longer-term control solution, and ultimately probably more effective measure, will be through breeding, with some promising results from trials comparing SBR-tolerant varieties versus susceptible varieties.
In the meantime, agronomists and experts are concentrating on finding agronomic measures that reduce risk, again mirroring the UK experience with virus yellows.
“We’re at the beginning of the race,” admitted Südzucker agricultural research coordinator, Achim Jesser, who’s been working in partnership with growers and grower associations in Germany to implement various control practices on farm. “But we have to find solutions quickly, otherwise we’ll lose sugar beet in our rotations.”
Various research projects are starting to help suggest what could work on farm. For example, KWS research at its field station in Seligenstadt, west of Frankfurt, has found that most of the yield damage happens during the period of peak planthopper flights.
In 2024, that coincided with a 10-day period from 20 June, while in 2025 it was a slightly longer 20-day period in mid-June, explained Carsten Stibbe, KWS R&D head of field station at IIRB’s recent 80th Congress in Cambridge.
“The key finding is there’s a beginning and an end, which indicates a chance for a control system – we just need to able to detect the beginning and end of flights.”
That could be one application of two complementary models using AI-based image analysis of sticky traps being developed by Dr Facundo Ispizua Yamati and colleagues from IfZ.
The first model identified cixiid planthoppers from other insects caught in traps to 94% overall accuracy, he reported, while the second model distinguished between the main SBR-relevant planthopper groups, with 99% accuracy.
KWS’ research also looked at the effectiveness of insecticides, finding the contact insecticide lambda-cyhalothrin gives up to 10 days control, with a combination with systemic insecticide acetamiprid providing some increased activity up to 15 days after exposure to planthoppers.
Südzucker’s research builds on those findings, trialling the use of combinations of insecticides and foliar fertilisers across small plot trials and in around 60 on-farm split fields.
These too showed promising results, with the combination of three sprays of a tank mix of contact and systemic insecticides providing 10-14% higher white sugar yield; adding in a foliar fertiliser boosted that to a 16% increase in both small plot and grower strip trials over untreated controls, reported Achim.
“Importantly, it’s economically feasible for the grower. They make more money if they spray compared with doing nothing.”
PROGRESSIVE RESEARCH
A second project had an even more ambitious scope. In four regions, Südzucker designated that all the growers and fields in the region were part of the trials, explained Achim.
In these trials, growers were asked to adjust their cropping rotation to grow spring crops rather than the typical winter wheat after beet, as well as to use insecticides and foliar fertilisers to protect and strengthen the beet crop.
Researchers monitored planthopper emergence from the spring crops versus winter wheat outside the designated project areas, finding 80% fewer planthoppers emerging in the spring crops.
“While there are economic questions [about growing spring crops], this could be part of the solution,” suggested Achim.
Visually, the beet in the region looked better too, he added. “But it’s all about did it improve yield? The short answer was yes, delivering around 20% more white sugar yield on average inside those regions compared with a 3km surrounding area.”
Armed with these results, last year Südzucker provided similar recommendations to all its grower base. The result, after three consecutive years of losing up to 1.3% sugar content year-to-year in the beet delivered to the factories in SBR-affected regions, was a 1% increase in sugars, said Achim.
“While it was a good year for beet, this gives us hope that these measures and farmers trying to do something about SBR are helping us to go in the right direction,” he concluded.
This article was taken from the latest issue of CPM. Read the article in full here.
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