Spring sickness has been around since the 1950s and possibly at least the 1940s and still we don't know exactly what causes it although there are suspects. It's very hard to study because you never know which fans or plants will get it in a given year, plus you have to wait a year between instances so testing ideas is slow going. Too often it is put down to weather conditions after the shoots have emerged but one thing we do now know is that it starts before the shoots first emerge in spring.
