Early Blight
Alternaria solani and Alernaria alternata
Pathogen
Fungus
Hosts
Potatoes, tomatoes (A. solani)
Symptoms
Spots on foliage are dark brown with circular rings giving a target appearance. These spots may merge to form dead patches. This disease can be differentiated from late blight as white mould-bearing spores do not develop around the foliage spots during humid weather conditions.
Development
Early blight, as the name implies, appears before the onset of late blight but does no spread throughout the foliage in UK potato crops as it does in warmer climates such as the USA. Early blight is comprised of two different species (A. alternata and A. solani) and these can only be differentiated in the laboratory by closely studying the spores. A. solani is more easily controlled by fungicides in the field. Carried over on plant debris in the soil which releases spores in the spring to infect newly establishing crops. Can also infect the tubers which act as an additional source of inoculum.
Favourable Factors
Hot, dry weather with extended periods of leaf wetness.
Importance
Historically, was not considered to be of economic importance in the UK. However in recent years it has become more conspicuous on the continent, Scandinavia and the UK, particularly in the warmer summers of 2010 and 2011. The reduced use of mancozeb in blight control programmes and the introduction of more susceptible varieties are also thought to have contributed to the increased incidence of this pathogen. The disease can cause yield losses if uncontrolled.
Control
Disease free seed
More susceptible varieties are being grown. Markies is the worst affected, but also found on Hermes, Maris piper, Maris Peer, Saturna, Vivaldi and Estima.
Crop rotation
Remove sources of inoculum such as crop debris and volunteers
Crops growing less vigorously or under stress from high soil moisture deficit or nitrogen deficiency are more at risk of infection
Fungicides applied to control late blight will also control the spread of early blight. Certain active ingredients have specific activity on early blight.
