Late Blight -- Take A Deep Breath!

A good friend and long time gardener just called me, wanting to pass along news "from the Extension Service" that because of the blight, tomatoes and potatoes can't be planted again in the same place for 3 years, and that only resistant hybrids can now be planted. She was apparently told the disease lives on in the soil, and wanted me to hasten and pass along this information.

Well, gees, take a breath! Yes, it is always good to rotate crops (though there is also the theory that in small home gardens you can't get them far enough away to matter), and yes, if you're into hybrids, you may find some of them have more disease resistance.

No, Late Blight does NOT live in the soil. Here's what I found on the Extension Service websites from Michigan and Ohio, and the Plant Pathology Department at Cornell in New York (at which point I stopped looking since there seems to be no disagreement, this otherwise excellent July 17 article from the NYT notwithstanding):

Late blight is caused by the fungus Phytophthora infestans. Unlike most pathogenic fungi, the late blight fungus cannot survive in soil or dead plant debris. For an epidemic to begin in any one area, the fungus must survive the winter in potato tubers (culls, volunteers), be reintroduced on seed potatoes or tomato transplants, or live spores must blow in with rainstorms. Disease development is favored by cool, moist weather. Nights in the 50’s and days in the 70’s accompanied by rain, fog or heavy dew are ideal.

In all liklihood, we in the Northeast have Big Biz to thank for this. By July 28, the NYT had more to report:

The source of the outbreak is being investigated by pathologists. Home gardens likely helped spread the infection: Lowe’s, Home Depot, Kmart and Wal-Mart all sold tomato seedlings with late blight in their garden centers from April to June. All are offering refunds or credits to gardeners who must destroy their plants.

(Personally, I wouldn't be surprised if that was arranged by our (not) friend, the big M.) Fat lot of good a refund to gardeners does for our farmers who have lost untold thousands of dollars in this epidemic.