Ergot (claviceps purpurea) is a fungal pathogen that affects all cereal crops and a number of other grass species. Infection only becomes apparent during grain formation, where individual grains are replaced by black fungal masses (‘ergots’), up to 2cm in length.
Although posing minimal effect to yield, standards for ergot content are strict, with a zero-tolerance stance taken by most processors.
This is due to the mycotoxins produced by ergot that are highly toxic to both humans and animals. Costly grain cleaning will be required of a contaminated load.
What to look out for
Ergot is not a seed-borne disease, however it is associated with contaminated seed.
Although tolerances are very low, ergot may be present in certified seed. The regulatory minimum standard allows for up to 3,000 ergot pieces in a half tonne seed bag, whereas the higher voluntary standard only allows up to 500 ergot pieces in a half tonne seed bag.
The first sign of ergot infection may be the development of honeydew at flowering, which is when spores first enter the ear.
Black ergots that are white inside then form in place of grains, which can be clearly seen in the field. Ergots are harvested with the grain and may be mistaken for rodent droppings in the heap.
Ergots only survive for around one year on the soil surface, although they can survive longer than this in storage.
Risk factors
Cool and wet conditions during flowering favours spore production, and the presence of host grass species also increases risk of spore spread.
Grass species known to spread ergot include blackgrass, ryegrass, cocksfoot, couch and annual meadow-grass.
Open flowering wheat varieties, or those with a prolonged flowering period are more susceptible to infection.
Prevention
There are a number of steps that growers can take to reduce the risk of ergot development.
- Avoid open flowering varieties, or those with a long flowering period.
- Reduce the presence of host species, through rotation extension with non-host species and careful management of grass weeds, particularly blackgrass.
- Ploughing to bury ergots to at least 5cm.
- Carefully manage grass margins, beetle banks, road verges etc. When sowing grass margins, consider later-flowering species and manage grass species known to spread ergot.
- Where possible, choose seed certified to the higher voluntary standard, or farm save your own seed where you can manage the ergot contamination yourself.
- Some seed treatments will provide a level of protection.
Spread and infection
Ergots, either from contaminated seed lots, or that have fallen to the ground from the previous harvest, germinate in the spring and produce mushroom-shaped spore bearing stroma.
The spores are distributed by the wind to open flowers of cereals and grasses. Spores then germinate in the flowers, causing an infection that leads to development of sticky honeydew.
This honeydew attracts insects which then transfer spores to further plants. Spores can also spread through rain splash and physical contact. Black ergot pieces then form in place of grain during grain formation.
You can find more information about ergot risks and management through AHDB and SRUC.
