Reports of Bonnie's Plants in the Northeast with Late Blight are in the news right now and I am sure many folks are worried about their tomato plants. This is an incredibly nasty disease that causes terrible looking lesions which start on the stems and move to the leaves.
Because of the distribution of plants all over the country by Bonnie's and others, and the fact that they don't know where it is coming from, Bonnie's greenhouses or at the stores, they are very concerned and have pulled plants off the shelves of several stores. This is akin to the situation with produce that is grown in factory farms, processed in very large scale and distributed all over the country. When there is an outbreak, it is almost impossible to control the spread.
If your plant shows signs of these particular lesions, they should be destroyed immediately, you will not be able to prevent the spread of the disease. Because the fungal spores travel airborne, it will move to your other plants and only get worse. If you don't have lesions like this, don't worry, you are probably just fine. We haven't had any reports of lesions on any of our plants and we don't have any reason to believe our plants have been contaminated since we don't sell in big box stores.
Fungicides can be used to prevent this disease and prevention is important if you live in areas where rainfall is extremely heavy for weeks at a time. This creates the perfect conditions for the spread of diseases.