Tarrytown, N.Y. – 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.

According to plant pathologists, this killer round of blight began with a widespread infiltration of the disease in tomato starter plants. Large retailers like Home Depot, Kmart, Lowe’s and Wal-Mart bought starter plants from industrial breeding operations in the South and distributed them throughout the Northeast. (Fungal spores, which can travel up to 40 miles, may also have been dispersed in transit.) Once those infected starter plants arrived at the stores, they were purchased and planted, transferring their pathogens like tiny Trojan horses into backyard and community gardens. Perhaps this is why the Northeast was hit so viciously: instead of being spread through large farms, the blight sneaked through lots of little gardens, enabling it to escape the attention of the people who track plant diseases.

It’s important to note, too, that this year there have been many more hosts than in the past as more and more Americans have taken to gardening. Credit the recession or Michelle Obama or both, but there’s been an increased awareness of the benefits of growing your own food. According to the National Gardening Association, 43 million households planned a backyard garden or put a stake in a share of a community garden in 2009, up from 36 million in 2008. That’s quite a few home gardeners who — given the popularity of the humble tomato — probably planted a starter or two this summer.

Here’s the unhappy twist: the explosion of home gardeners — the very people most conscious of buying local food and opting out of the conventional food chain — has paradoxically set the stage for the worst local tomato harvest in memory.

So what do we do?

For starters, if you’re planning a garden (and not growing from seed — the preferable, if less convenient, choice), then buy starter plants from a local grower or nursery. A tomato plant that travels 2,000 miles is no different from a tomato that has traveled 2,000 miles to your plate. It’s an effective way to help local growers, who rely on sales of these plants before the harvest arrives. It’s also a way to protect agriculture. If late blight occurs in a small nursery it’s relatively easy to recognize, as straightforward as being able to see the plant, recognize its symptoms and isolate it before it has a chance to spread.

This is less of an option on a farm that’s spread out over dozens of acres, nor is it likely once the plant gets to a large retailer. A plant pathologist from Cornell told me she visited one such store and noticed the tomato plants were infected with blight. She immediately reported it to the manager, who said he couldn’t remove the plants without approval from his superiors (which would take time). The pathologist returned a week later to find that the plants were still there.

In fact, this late blight outbreak appears to be a classic example of what Charles Perrow, a sociologist, calls a “tightly coupled” accident. With tight coupling — lots of tomatoes grown in one place, say, or distributed by one large retailer — failures in one part of the system can quickly multiply. The damage cannot be as readily controlled. The recent spike in food-borne illnesses is another example of the problems associated with an overly consolidated food chain. E. coli’s been around for a long time; what’s new is how quickly and widely it spreads when there are only a few big meat producers.

There’s another lesson here for the home gardener. When you start a garden, no matter how small, you become part of an agricultural network that binds you to other farmers and gardeners. Airborne late blight spores are a perfect illustration of agriculture’s web-like connections. The tomato plant on the windowsill, the backyard garden and the industrial tomato farm are, to be a bit reductive about it, one very large farm. As we begin to grow more of our own food, we need to reacquaint ourselves with plant pathology and understand that what we grow, and how we grow it, affects everyone else. (Potato farmers in the Andes, for example, plant disease-prone varieties at high altitudes where the cold keeps pathogens in check — to protect themselves and their neighbors. They don’t get as big a harvest, but they decrease the risk of an epidemic.)

Government can help. For all the new growers out there, what’s missing is not the inspiration, it’s the expertise, the agricultural wisdom and technical knowledge passed on from generation to generation. Congress recognized the need for this kind of support almost 100 years ago when it passed the Smith-Lever Act, creating a network of cooperative extension services in partnership with land-grant universities. Agricultural extension agents were sent to farms to share the latest technological advances, introducing new varieties of vegetables and, yes, checking the fields for disease.

The cooperative extension service is still active, but budget cuts have left it ill equipped to deal with a new generation of farmers. The emphasis now is on reaching farmers through mass e-mail messages and Web-based dialogues, with less hands-on observation. That’s like getting a doctor’s check-up over the phone. More agents in the field during those critical weeks in June might well have resulted in swifter, more effective protection of the plants: early detection of any disease requires a number of trained eyes.

The food community has a role to play, too — by taking another look at plant-breeding programs, another major fixture of our nation’s land-grant universities, and their efforts to develop new varieties of fruits and vegetables. To many advocates of sustainability, science, when it’s applied to agriculture, is considered suspect, a violation of the slow food aesthetic. It’s a nostalgia I’m guilty of promoting as a chef when I celebrate only heirloom tomatoes on my menus. These venerable tomato varieties are indeed important to preserve, and they’re often more flavorful than conventional varieties. But in our feverish pursuit of what’s old, we can marginalize the development of what could be new.

That includes the development of plants with natural resistance to blight and other diseases — plants like the Mountain Magic tomato, an experimental variety from Cornell that the Stone Barns Center is testing in a field trial. So far there’s been no evidence of disease in these plants, while more than 70 percent of the heirloom varieties of tomatoes have succumbed to the pathogen.

Mountain Magic is an example of regionalized breeding. For years, this kind of breeding has fallen by the wayside — the result of a food movement wary of science and an industrialized food chain that eschews differentiation in favor of uniformity. (Why develop and sell 20 different tomato varieties for 20 different microclimates when you can simply sell one?)

Breeders in regions vulnerable to late blight should be encouraged to select for characteristics that are resistant to it, in the same way that they select for, say, lower water demands in the Southwest. While they’re at it, breeders could be selecting for flavor and not for uniformity, shipping size and shelf life. The result will mean not just tastier tomatoes; it will translate into a food system with greater variety and better regional adaptation.

Healthy, natural systems abhor uniformity — just as a healthy society does. We need, then, to look to a system of food and agriculture that values and mimics natural diversity. The five-acre monoculture of tomato plants next door might be local, but it’s really no different from the 200-acre one across the country: both have sacrificed the ecological insurance that comes with biodiversity.

What does the resilient farm of the future look like? I saw it the other day. The farmer was growing 30 or so different crops, with several varieties of the same vegetable. Some were heirloom varieties, many weren’t. He showed me where he had pulled out his late blight-infected tomato plants and replaced them with beans and an extra crop of Brussels sprouts for the fall. He won’t make the same profit as he would have from the tomato harvest, but he wasn’t complaining, either.

Sometimes giving in to nature can be the biggest victory of all.