![]() The cultivation of largely immune varieties, the use of healthy seed and the control of second-growth potatoes from the previous year in the successive crops are the most effective preventive measures. With susceptible varieties, an infested potato crop can completely fail within a few days in humid and warm weather. The Phytophthora infestans pathogen can also occur at shoot tips, stalks and petioles. In the early hours of the morning, a greyish-white layer of fungus can be detected on the underside of the leaf, at the light-green zone of transition from diseased to healthy tissue. Mostly forming from the leaf edge or leaf tip, these patches quickly increase in size in damp weather. Many cycles of early blight spore production and lesion formation occur within a single growing season once primary infections are initiated. The yellowish-green patches on the lower leaves soon change to chocolate-brown. humid conditions, sporangia located in leaves and stems are washed off and pulled down to the soil where they can produce zoospores and infect tubers near the soil surface. Infected plants can normally be recognised by the browning of the base of the stem, or of individual parts of the stem. ![]() Primary infestation can be detected in the spring on individual plants scattered throughout the crop, and can usually be traced back to infested planting material, although potato-waste dumps and second growth are also possible sources.įurther spread to healthy plants (secondary infestation) from primary outbreaks occurs mainly downwind. The disease is caused by Phytophthora infestans and is infamous for causing the potato famine in Ireland in the 1840s. Potato late blight is caused by the pathogen Phytophthora infestans. Late blight is a disease that can infect many solanaceous plants such as tomato, potato, and solanaceous weeds, however, there have been no reports of late blight in pepper or eggplant. ![]()
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