Ergot in cereals: All you need to know about spread, symptoms & management
Ergot Claviceps purpurea is a fungus that affects cereals and grasses around the world. The fungus only infects open, unfertilised flowers, which is why it primarily affects flowering rye that has been open for a long time.
The problem comes when the fungus develops fruiting bodies which contain highly toxic alkaloids that are highly poisonous to humans and animals. Yield losses resulting from the ergot disease are usually relatively low, however, farmers are affected by the lower prices commanded by the contaminated rye. No immediate measures exist to manage ergot. Preventive measures such as GRAINGUARD, offer viable options and are effective. This article explores the deciding factors and why they make sense.
Ergot spread: worldwide and primarily on rye
Ergot Claviceps purpurea is found worldwide. It is most common in cereals with long open flowering periods, and which require time for pollination and fertilisation. For this reason, rye is particularly susceptible to ergot as it is dependent on cross-pollination, followed by triticale which is facultatively cross-pollinated. The fungus is not limited by self-pollinating cereals like wheat, however, infestations are less common. A further 600 grasses can also become infected with ergot fungus. Ergot infestations vary greatly across regions and year by year as the fungus is highly dependent on cool, wet conditions coupled with high humidity. Some years are severely affected, while others see hardly any symptoms. Since the fungus mainly infects rye, it is inevitably more common in areas with heavy rye cultivation.
The ergot life cycle
The ergot fungus belongs to the group of tubular fungi (Ascomycota). Ergot sclerotia is its permanent form. Sclerotia overwinter at or just below the soil surface. Under favourable conditions, they germinate in spring and form bottle-shaped fruiting bodies (Perithecia). Ascospores form in the tubes inside (the asci) and are ejected when the grain flowers. If the spores land on plants not yet been fertilised, they infect the ovary via the stigmas (primary infection). Asexual conidia then develop in the ovary and a sugar-containing sap is produced which is commonly referred to as honeydew. Rain splash, insects and contact between the ears spread the honeydew to other unfertilised stigmas and trigger secondary infections. Around four to six weeks later, the clearly visible sclerotia develop from the primary and secondary infected fruit plants in parallel with grain ripening. These then either fall to the ground or are harvested with the grain.
The first symptoms of an ergot infestation occur during flowering when a yellowy, sticky secretion is produced on the flower head. This is the sugar-containing honeydew which is formed once the primary infection has taken place. As the grain ripens, deep red or purple sclerotia form with a white interior. The ergot elongates and curves like a horn. It is usually clearly visible on the ear as it is often much larger than a grain kernel. Ergots can vary from a few millimetres in length up to four centimetres.
Factors promoting ergot infestations
Prevailing weather conditions are the decisive factor in ergot Claviceps purpurea infestations. A cold, wet spring coupled with high humidity favours fungus germination and growth, however, these conditions are also perfect for infection. This is because the wet cold prolongs flowering and means that the fungus encounters more unfertilised plants.
The number of unfertilised flowers is even higher in unfavourable weather as it prevents the pollen drift necessary for pollination. (Incidentally, the effect of a lack of pollen can often be seen in the sown margins of stands. Cereals facing the wind flower longer due to the lack of pollen and are therefore more often affected by ergot).
Reduced plant numbers in stands can act as an additional amplifier as this leads to uneven flowering. Flowering grasses on field margins or emerging in the field are also conducive to ergot infestation as they become intermediate hosts for the fungus.
Management of ergot in cereals
There is no immediate management available for ergot. Preventive measures, however, offer an effective way to minimise the risk of this disease, while keeping symptoms to a minimum.
The first step is to review the grain cultivation site. This should be open to the wind so that it promotes pollen drift and rapid pollination.
Ergot can survive in the soil for one to three years, therefore crop rotation needs to be set up to provide a sufficient break between rye and triticale. It is advisable to integrate broad-leaf plants into crop rotation. In situations where a crop of rye follows another crop of rye, the disease risk can be reduced with intensive ploughing of the sclerotia. Ploughless tillage after rye should be avoided if possible. As a minimum, it must be carried out to a depth of no less than five centimetres.
Measures should be taken to manage and promote pollination so that the pathogen has less time to infect the flowering plants. It makes good sense to focus on rye varieties with improved pollen release.
Using sclerotia-free seed is important during sowing, and purified seed offers a safe option.
Mowing grasses around the field edges before flowering is advisable, as these grasses are also prone to the disease and can act as host plants and promote reproduction.
Ergot is highly toxic - thresholds apply
If, despite preventive measures being taken, the fungus Claviceps purpurea infects a crop, grading is necessary because the sclerotia of the ergot fungus contain alkaloids that are toxic to animals and humans. If consumed, ergot poisoning can be severe, ranging from gastrointestinal disorders to loss of limbs and miscarriage. To protect consumers and livestock, the thresholds for ergot must be observed. These are currently 0.05 per cent in food and 1000 mg/kg in feed, which corresponds to 0.1 per cent. In 2024, the threshold for food will be reduced to 0.02 per cent.
To observe the toxic limit, special procedures are used to sort ergot from grain. Harvesting offers an early option to separate as many sclerotia from the crop as possible by adjusting settings on the combine harvester. Grain needs to be well ripened for this to succeed. Harvesting must be carried out in dry weather. Depending on the intensity and spatial occurrence of the disease, it is possible that only isolated areas of the field are affected, offering the possibility of harvesting and handling these separately.
After harvesting, cleaning is carried out in mill with the appropriate cleaning systems in place. Sorting is carried out according to weight and colour. For severely affected grain, this process may need to be repeated several times.
Ergot in the Middle Ages
Thanks to the thresholds and purification methods available these days, ergot no longer plays a role in today’s nutrition. In the Middle Ages, however, ergot was the cause of countless epidemics. At the time, the toxicity of the alkaloids contained was not known, therefore consumption of food containing up to twenty per cent contaminated rye repeatedly led to mass poisonings. These epidemics became known as St. Anthony's fire and often had devastating consequences, with symptoms ranging from hallucinations to convulsions and paralysis. Many people died or were left with severe impairments after losing extremities. Ergot also contains chemicals that stimulate contractions meaning miscarriages are frequent.
It was not until the 17th/18th century that people came to understand the link between these epidemics and ergot. From this point on, ergot has been increasingly separated from the crop, reducing the chance of poisonings. Thanks to the change in dietary habits in favour of potatoes recently, St. Anthony's fire has largely disappeared, however, ergot is still used in small doses in medicine.
Great results with GRAINGUARD
Treatment of seeds with GRAINGUARD creates the optimal conditions for a good start and stress-resistant crop development. Plants treated with GRAINGUARD benefit from improved nutrient and water uptake thanks to excellent root growth.
Overall, trials have clearly demonstrated that GRAINGUARD improves plant vitality and assured yield stability, particularly in difficult conditions.
Read more about GRAINGUARD.