Feb 152011
 
Tomato Flower
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IF the hardship of growing vegetables and fruits in the Northeast has made anything clear, it’s that the list of what can go wrong in the field is a very long one.

We wait all year for warmer weather and longer days. Once we get them, it seems new problems for farmers rise to the surface every week: overnight temperatures plunging close to freezing, early disease, aphid attacks. Another day, another problem.

The latest trouble is the explosion of late blight, a plant disease that attacks potatoes and tomatoes. Late blight appears innocent enough at first — a few brown spots here, some lesions there — but it spreads fast. Although the fungus isn’t harmful to humans, it has devastating effects on tomatoes and potatoes grown outdoors. Plants that appear relatively healthy one day, with abundant fruit and vibrant stems, can turn toxic within a few days. (See the Irish potato famine, caused by a strain of the fungus.)

Most farmers in the Northeast, accustomed to variable conditions, have come to expect it in some form or another. Like a sunburn or a mosquito bite, you’ll probably be hit by late blight sooner or later, and while there are steps farmers can take to minimize its damage and even avoid it completely, the disease is almost always present, if not active.

But this year is turning out to be different — quite different, according to farmers and plant scientists. For one thing, the disease appeared much earlier than usual. Late blight usually comes, well, late in the growing season, as fungal spores spread from plant to plant. So its early arrival caught just about everyone off guard.

And then there’s the perniciousness of the 2009 blight. The pace of the disease (it covered the Northeast in just a few days) and its strength (topical copper sprays, a convenient organic preventive, have been much less effective than in past years) have shocked even hardened Hudson Valley farmers.

Jack Algiere, head vegetable farmer at the Stone Barns Center for Food and Agriculture (where I have a restaurant that purchases from the farm), lost more than half his field tomatoes in three days. Other organic farmers were forced to make a brutal choice: spray their tomato plants with fungicides, and lose organic certification, or watch the crop disappear. Even for farmers who routinely spray, or who reluctantly spray precautionary amounts, this year’s blight lowered yields. (Fungicides work only to suppress the disease, not cure it.) As one plant pathologist told me, “Farmers are out there praying and spraying.”

Of course, farmers aren’t the only ones affected. If you love eating flavorful organic field tomatoes, good luck — they’ll be as rare this summer as a week without rain. And those that survive will cost you; we’re already seeing price increases of 20 percent over last year.

So what’s going on here? Plant physiologists use the term “disease triangle” to describe the conditions necessary for a disease outbreak. You need the pathogen to be present (that’s the late blight), you need a host (in this case tomatoes and potatoes) and you need a favorable environment for the disease — for late blight that’s lots of rain, moderate temperatures and high humidity.

Does that last bit sound familiar? It has been the weather report for the Northeast this summer, especially in June. Where we saw precipitation fit for Noah’s Ark, late blight found something akin to a four-star hotel. Those soggy fields and backyard vegetable plots? Inviting, and all too easy to check into.

But weather alone doesn’t explain the early severity of the disease this year. We’ve had wet, cool summers in the past, but it’s never been this bad. Instead we have to look at two other factors: the origin of the tomato plants many of us cultivate, and the renewed interest in gardening.

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