Late Blight

Symptoms

Large gray-green water-soaked blotches that brown within days, white sporulation on leaf undersides in humid mornings, and firm brown greasy patches on fruit. Spreads regionally on storm fronts and can level a planting in under two weeks, the Irish famine pathogen on its second host.

Management

Because inoculum blows in, sanitation alone cannot hold it; resistant varieties carrying Ph-2 + Ph-3 (Mountain Magic, Defiant PhR, Iron Lady) changed the game for growers in blight-prone regions. Destroy volunteer potatoes and infected plants immediately, cull piles are the classic season-starting source. Regional monitoring networks track outbreaks in real time.