Late blight—Phytophthora infestans
On leaves, late blight lesions typically first appear as irregular, small, pale to dark green water-soaked
spots that are surrounded by a zone of yellowish tissue. Lesions may expand rapidly and become brown to
purplish black. White sporulation of the fungus may be observed at the periphery of lesions, principally
on the underside of leaves. On stems and petioles, lesions are brown to black and may also support sporulation
of the fungus. Tubers develop a firm brown decay.
Destroy and remove cull piles and volunteer plants. Use certified tubers. When planting tubers, keep
them covered with soil "hills." Bordeaux
mixtures may be used as a protectant. When late blight
has developed on foliage and tubers are at a risk of infection, make sure that vines have been completely
dead for 2 - 3 weeks before harvest as the fungus does not survive very long in dead foliage. Avoid harvesting
under wet conditions. Eliminate all tubers and plants after harvest.
blight symptoms on potato leaves
decay in potato tubers