In an effort to breed perennial ryegrass that was resistant to the weevil, researchers in New Zealand inadvertently selected strains that were susceptible to the fungus.
With greater use of these susceptible cultivars, the fungus which is present in the seed, spread more widely with a consequent increase in perennial ryegrass staggers.
Recumbent animals may display tetanic spasms and may die through misadventure, dehydration, starvation, loss of rumen function or predation.
The chief danger to stock at this stage is caused by their lack of coordination, which may result in accidental death by falling in awkward places such as ditches and ponds.
Horses are particularly prone to this disease because of their habit of biting close to the ground, and sparse pastures may encourage heavier grazing with greater intake of infected material.