Sunday, October 11, 2009

Early steps to stop late blight

By Jenna Burleigh

Q: What is late blight?

A: Phytophthora infestans, a fungus-like oomycete pathogen, called late blight, is an infection that kills tomato and potato plants. An oomycete is "a simple organism similar to a fungus that feeds on rotting material or living plants by absorbing nutrients through fine threads," according to MSN Encatra. This is the same infection responsible for the severe potato famine in Ireland in the 1850s, forcing many to starve or emigrate.

Late blight can affect a plant at any time in the growing season, and if detected, should be promptly destroyed. The disease can infect the leaves, stems, fruits and tubers of tomato and potato plants, which are susceptible only when wet, according to this article. However, this includes if the plants are moist from dew, irrigation, sprinklers, and even fog.

Q: How do spores infect plants?

A: The disease can only survive on living tissues. It usually survives through the winter on potato tubers, which spread the infection when replanted as seed. Infected plants grow and develop noticeable signs of the disease. Some signs include dark-colored abrasions on the stem of the plant or on the fruit or tuber. Leaves will turn brown and decay, or fuzzy, white spots can appear on the leaves, containing spores. Spores spread by wind or splash onto new hosts with rainfall. It was once thought that late blight wouldn’t spread after harvest, but it can, according to this site.

Q: What will stop the spread of late blight?

A: There are several actions you can take to protect your crops from late blight. The best measures are preventative steps. When purchasing your seed for the new growing season, make sure it is certified healthy seed, and be sure to ask if there were any signs of late blight during the harvest of these seeds.

Inspect all of your seed carefully. If you see black or purple-colored abrasions on tubers, dispose of them properly. This does not just mean throwing the infected seed away, but either burry it two feet below the surface, feed it to livestock, freeze it, or completely till it into the soil if your previous crop was ruined by late blight.

One simple method to help reduce the risk of late blight to tomato and potato plants is to make hills around the roots of the plants. Placing as much soil as possible around the plants will help protect tubers and roots from spores that filter through the soil.

If you have discarded tubers from a previous harvest, without properly disposing of it, make sure to kill the plants if they start to grow. Late blight may have infected it, and if spores are allowed to grow, this could eventually infect your new crop, as well as surrounding plots.

Fungicides are available that will help prevent late blight. Once the disease has infected a crop, it is difficult to save it unless it is treated with a fungicide with systemic activity (meaning they penetrate the plant tissue), within 24 hours of infection. Even then, it may be too late to save the plant. Warm, dry weather, both day and night, would naturally stop the infection, at least temporarily. However, the plant should be destroyed before the infection spreads to other plants. Fungicides are most effective when applied regularly.When storing potatoes, growers should keep them in a cool, dry place. Keeping them put of moist areas ensures that late blight cannot infect the tubers, because it needs moisture.

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