Late Blight Reemerges in 2010 Gardens

The tomato/potato late blight has reemerged for the 2010 growing season. The return of Phytophthoria infestans is not good news for backyard gardeners. Once infected, the tomato plants turned sickly black within days after being infected and are dead in about a week's time. While not harmful to humans, it is a deadly pathogen for prized tomatoes and potatoes.

Once the plants become infected, they need to be immediately destroyed. There is no hope for infected plants. The late blight, the most severe of any tomato or potato disease, is a communal disease; it can spread rapidly through neighborhoods, counties and states. It is a problem for all and the response necessarily needs to be communal.

Gardeners can take several precautionary steps. It is important to monitor both tomato and potato crops frequently. If a suspicious plant is discovered, contact the local extension office, for proper identification. Late blight is generally characterized by pale green or brown spots on the upper leaves, lesions on the leaves and the presence of a white downy substance. The stems and the fruits can also show similar signs. If no suspicious discolorations or lesions are discovered, a spray program can help the 2010 tomato and potato crop

There are commercial sprays available which can help backyard gardeners, but the sprays are only effective if no blight has been discovered. Many commercial growers have already begun spraying crops but some home gardeners, similar to last year, could be unaware of the blight's renewed march. Some avid gardeners, aware of the latest 2010 outbreak, will rely on homemade sprays such as manure tea or a baking soda spray; other fungal sprays are available at many garden supply centers. However, any spray program, commercial or home brew, must begin before the blight arrives.

In 2009, the late blights began in a nursery in the south which shipped tomato plants to many box stores further north. Unfortunately, many unaware home gardeners purchased the infected plants and the late blight spread rapidly. Adding to the severity of the problem were the weather conditions experienced in much of eastern North America in 2009; the cool and rainy summer in 2009, were ideal conditions for the late blight. As the season came to an end last year, late blight had spread from the the eastern coast to well beyond the Mississippi and in large areas of Canada

A somewhat similar discovery of the late blight occurred in June of this year in Pennsylvania where the late blight was discovered in a monastery garden in nearby Blair County. Those plants were traced to a local nursery in nearby Somerset County, Pennsylvania which sold plants to many other customers as well as the monks. The nursery has not been identified. Agricultural officials in western and central Pennsylvania are not hopeful for a successful tomato or potato harvest in that region.

Other earlier and sporadic outbreaks of the late blight have been discovered in several other states: New York, Massachusetts, Delaware, Maryland, Indiana, Wisconsin and Maine for example, have reported cases of the deadly late blight. The source of the blight in those states, unlike the Pennsylvania case, have not yet been pinpointed or identified to date this year.

The late blight travels quickly and is frequently carried upwards of forty miles by the wind. The spores can also be spread by rain, machinery, people and wildlife. The late blight is a devious disease; it can also be present in solanaceous weeds; hairy nightshade and bittersweet nightshade are two of the most common culprits. Those weeds should be removed. Weed control, a normal good gardening practice, is an important management action in the fight against the blight.

The late blight, luckily for now, can not survive the winter; it needs living tissue to survive. The bad news is the blight spores have could have mutated and could be able to survive winter weather. Researchers are also investigating the possibility of another new and trickier strain of the disease.

The late blight spore can survive winter on underground potatoes missed during the fall 2009 harvest season. It is important to dig all potatoes, particularly if the blight was present. The early spring "volunteer" potatoes that sprout, should be removed because of the possibility of contamination. Agricultural officials also recommend destroying any volunteer tomato plants as well.

It is always a good idea to never compost plants of the nightshade family which include tomatoes, as well as eggplants, peppers, tobacco and potatoes, including sweet potatoes. If the plants are suspected of being infected, they should be burned or placed in plastic bags, allowed to remain in the hot sun for several days and then taken to a landfill. At the end of the season, spent tomato plants and rotting tomatoes should be disposed in a landfill or burn pit.

The late blight will not survive in tomato seeds. One possible action gardeners can take to avoid contamination is to start seedlings from seed saving or from seeds from reputable seed dealers. If a potato crop is to be grown, use certified seed. Crop rotation, good garden practices, such as cleanliness and attention to plant details can be effective in managing late blight problems for the 2011 season.

Researchers are developing tomatoes which are resistant to the late blight, however, questions remain regarding expense, availability, taste and growth habits. Late blight can be controlled; it is a community disease and the solution is everyone working together. As the disease evolves, different management techniques will be needed for the future.

The only other options are expensive tomatoes that taste something like cardboard.