Ramularia Leaf Spot
Ramularia on a younger and older beet leaf (Photo J. Hill)
Pathogen
Fungus
Hosts
Sugar Beet
Symptoms
It appears first on older leaves as brown-grey spots with dark edges. Under a microscope or powerful lens, small white spots can be seen emerging through the stomata. Under humid conditions, similar looking spots occur on Cercospora infected leaves but are distinguished from Ramularia by their black colour. Other distinguishing factors for Ramularia are: The lesions:
Go through the leaf to the other side
Are rectangular in shape
Surrounded by a chlorotic yellow halo
Reddish/brown in colour
Development
It is thought to overwinter on crop debris and can also be seed-borne.
Favourable Factors
Ramularia prefers cooler conditions than powdery mildew - around 17C - and infection only occurs when relative humidity exceeds 95% so it is mainly observed from September onwards.
Importance
It seldom causes significant yield losses in the UK unless it is so severe that leaves are lost and newly debeloping leaves use up accumulated energy from the root. Where disease pressure is severe sugar yield loss can be as much as 25%.
Control
Rotation of up to 4 years
Foliar fungicides should be applied to disease onset (usually late July - Early August) and if lifting beet beyond October a second application should be made 3-4 weeks later.
