Phytophthora infestans belongs to a group of plant pathogens commonly called “water molds” because of their affinity and special adaptations to water. These fungicides were previously very effective against late blight and commonly used by commercial growers for control of late blight. To make matters worse, these strains had developed pesticide resistance to several groups of systemic fungicides. In 2009, new strains identified in the mid-Atlantic region were found to be very aggressive on tomato in comparison to the more endemic strains that prefer potato as a host. When late blight is present in a location (e.g., overwintered) or is introduced (e.g., on transplants or by wind currents carrying inoculum) and environmental conditions are favorable, devastating crop loss can result if preventative control measures have not already been implemented.Ī recent problem that makes late blight more challenging to control is the appearance of new strains of P.

However, in major potato-growing regions of Virginia, such as the Eastern Shore, the pathogen may overwinter on potato tubers or on greenhouse tomato plants, making the disease a potential threat each year. In many areas of Virginia, late blight is not typically an annual problem. During wet, cool weather, crop loss due to late blight can be rapid and unstoppable if preventative controls have not been used. Wet, cool environmental conditions, such as those prevalent during the 1840s in Ireland, favor development of late blight. The Irish Potato Famine is a devastating example of the epidemic potential of late blight.

This famine resulted in the death of more than 1 million people and the displacement of nearly 2 million more during a short, five-year period. It has historical significance as the cause of the Irish Potato Famine during the 1840s. Late blight, caused by Phytophthora infestans, is an important and destructive disease on potato and tomato.

Early and late blight of potato