Peter Davies and Mark Scherzer are the owners of Turkana Farms in Germantown, NY. This week Peter writes: Just the other day I was looking on the bright side of the rather dry, hot spring we have been having here in Columbia County. At least, I thought, these weather conditions will prevent the late potato (and tomato) blight that wiped out our tomato crop last year. But my ears pricked up several days ago when Michelle Norris on NPR’s All Things Considered (who grew up in Chatham) announced that a basil blight, a very aggressive fungal disease named downy mildew, is now plaguing the Northeast and South. Wanting to know more, I googled “basil blight” and was disturbed not only to learn that downy mildew is well established in our region but, much to my dismay, that there is a good chance, in spite of our very different weather conditions this year, that potato (tomato) late blight will be returning as well. Do we, I now wonder, face a summer without both locally grown tomatoes and basil? I won’t repeat the information and advice on the late potato blight offered in my earlier bulletin “Tomatoes With Trepidation”, but refer you to Rural Intelligence’s archives should you want to review it. And I also suggest you look at the update provided by Meg McGrath, associate professor plant pathology at Cornell: So far, 33 New York State counties have reported late potato (tomato) blight infections, but up to now Columbia County seems to have escaped, Ominously, Dutchess County to the south and Rensselaer to the north have not.
But let’s look at the other fungal threat, this one to sweet basil, the mainstay herb of summer. We were late getting our Genovese and Thai basil planted this year, so we are still at the seedling stage and have nothing to examine yet. But those of you further along should examine the upper surfaces of your basil leaves for faint yellow bands, and the undersides for tiny grayish, almost purplish specks. These symptoms show up two weeks after the initial infection. Once the symptoms appear, it is not long before the leaves turn yellow, brown, and grey, making them unappetizing in appearance. It is important to be especially vigilant on your garden rounds during periods of heavy rains and high humidity. The home grower can control the disease by daily examining the plants and carefully, so as not to shake loose the fungal spores, removing the diseased leaves, which should be bagged to prevent dispersion. It is by wind-carried spores that the fungus is most commonly spread. Some advise harvesting the entire plant at the first sign of infection and bringing it to table or processing it for pesto (the disease is not toxic to humans). For large scale growers the logistics of containing the fungus are, of course, much greater. There are already cases farther south in which farmers have had to destroy entire crops. Affected growers are replanting and turning to organic fungicides, and vigorously culling any infected plants.
There are some preventive measures that we can still take this summer. According to McGrath, organic fungicides have limited effectiveness. But there are other things one can do. Basil grown in open, sunny areas is far less vulnerable than plantings in shadier beds with poor air circulation. And a constant supply of basil is possible, even in these adverse conditions, if one plants basil in waves every few weeks in different corners of the garden. There are also varieties of basil which seem disease resistant, but unfortunately, not the sweet basil or Thai varieties. Lemon and purple basil seem more resistant, and two varieties, pepper basil and spice basil, don’t seem affected by the fungus at all. Apparently now that we have the late potato blight and basil blight in our region, we can expect annual visitations from now on. Climatic conditions and the degree to which we are all vigilant in containing the infections will determine the degree to which our future crops will suffer. It seems strange that things we have always grown, vegetables we have always taken for granted as sure-fire producers, are becoming so vulnerable. It seems that globalization is one of the primary factors in this change. The basil blight was first reported in Uganda in 1933 and not reported again until 2001 in Switzerland, and now in 2010 it is at our doorstep. How has downy mildew made this incredible journey? Not only is the downy mildew spread by wind born spores, it is also, unfortunately, capable of infecting seeds. Up until now I have been admiring the growth of my tomatoes from afar and have taken the emerging rows of basil completely for granted. But on my next visit to the garden I’ll be giving these plants a special scrutiny. —Peter Davies
