In the typical life history of late blight in Maine (Figure 1), the pathogen persists from year to year only in potato tubers and usually spreads from sprouting tubers in cull piles from volunteer potato sprouts from culls left in the garden or field while harvesting and, less commonly, from planting diseased seed. Let’s look at what differed in 2009, and what can we do in 2010. Late blight occurs regularly in Maine, but usually it is spotty and not severe – and usually it does not affect tomatoes. The fungus is called Phytophthora infestans, which may sound familiar to those who remember history, because this organism was responsible for widespread potato problems in Ireland in the mid-1800s. Late blight is caused by a fungus with great similarity to some algae, which helps explain why it needs lots of moisture to do well. I have repeatedly stressed that understanding the biology of the organism that causes the disease is the first step in avoiding it. Some of you may be tired of hearing about it, but whether the crisis repeats in 2010 depends greatly on the weather and on what gardeners and farmers do to prevent the disease. Information for Prospective Host FarmersĪs everyone knows, last summer was wet and late blight was widespread on farms and in gardens.Information for Prospective Apprentices.Russell Libby Agricultural Scholar Awards.If the disease is present in the area, follow a 5- 7 day fungicide schedule, using fungicides recommended specifically for late blight control.Preventative fungicide sprays for early blight, Septoria and anthracnose protect against late blight.
Fruit symptoms are unlikely to be confused with other diseases, except buckeye rot however, late blight causes the fruit surface to become rough. Symptomatic leaves can be sealed in a plastic bag with a damp paper towel overnight, then checked for a gray to white moldy growth on the underside. Key diagnostic features on foliage are lesions that are not stopped at leaf veins. The organism can travel great distances by wind. The disease may overwinter in plant debris or cull piles (potato or tomato). The fungus grows most actively from 15- 21☌ (59- 70☏). Lesions on fruit appear as firm greyish-green to brown, rough, irregular shaped blotches, which rapidly enlarge.īuckeye rot (Fruit symptoms are unlikely to be confused with other diseases, except buckeye rot however, late blight causes the fruit surface to become rough.) Under favourable conditions, the pathogen can blight the foliage so quickly, that it appears the plants were hit by frost. These stem lesions may quickly girdle the stem and kill it. Brownish cankers may appear on leaf petioles and stems. On the underside of leaves, spots may develop a grey to white moldy growth, especially under conditions of high humidity. A pale yellow or green halo may surround the leaf lesions. Initial leaf symptoms are pale green to brown water-soaked spots, which enlarge rapidly and become brown to purplish-black. This disease is easily spread by wind and can rapidly destroy the crop. However, late blight causes the fruit surface to become rough. Fruit symptoms are unlikely to be confused with other diseases, except buckeye rot. Cool nights and warm days, with moist weather, are ideal for disease development. The late blight fungus prefers temperatures from 15- 21☌ (59- 70☏). Fruit lesions are firm, rough, and greasy-looking, with greyish-green or brown blotches.Brownish cankers on leaf petioles and stems may girdle and kill the plant.A grey-to-white moldy growth may develop on the underside of infected leaves, especially under conditions of high humidity.Pale green-to-brown water-soaked spots develop on the leaves lesions enlarge rapidly and become brown to purplish-black.