Once there was a fertile valley that was blessed with mild climate, abundant water and good soil.

Prosperous farmers grew many varieties of conventional crops, and sold great quantities of their yields at markets in faraway countries.

Other farmers proudly grew crops that were certified by the government as “organic” – free of pesticides and other toxins that controlled agricultural pests but also harmful to humans and the environment. Organic products were sold mostly to local, health-conscious consumers.

One day, a salesman came to the valley peddling the seeds of an entirely new type of plant. “Nature could never create plants like these,” he boasted to a gathering of farmers. “They’re ‘GE,’ that’s ‘genetically engineered’ in a laboratory. They’re really two very different organisms joined together – like a mermaid.

“You don’t need pesticides to grow them because we’ve attached genes from pesticidal bacteria to their genes. They’ll kill bugs that try to eat them. That will save you money and protect the environment from pesticides.”

“But I don’t use pesticides,” said a skeptical organic farmer.

Nevertheless, a few of the conventional farmers decided to try the new plants and found they grew well and repelled insect pests as advertised.

But no one foresaw that wind and insects would spread pollen from the GE plants to related plants on nearby conventional and organic farms and even to wild plants. Once pollinated, those plants passed their pesticidal GE genes to their offspring.

Then the conventional farmers whose crops now carried GE genes made a shocking discovery: They could no longer sell their yields on the international market because many foreign countries, fearing genetic contamination, banned GE foods. These farmers lost money dumping their yields on secondary markets.

Many organic farmers quickly lost their certified-organic status, because the GE genes their crops now harbored were officially labeled as a pesticide. Frequently, these small farmers went out of business, and were forced to sell their farms to large landholders at reduced prices.

Farmers naturally tried to destroy the contaminated crops by burning, plowing and replanting their fields. But the GE genes persisted year after year, perhaps being reintroduced from contaminated wild plants.

Ultimately, the valley’s farming economy was devastated.

Thus ends my cautionary parable about GE plants. I hope it’s entertained you. But is it plausible?

We know there have been many documented cases of reciprocal “gene flow,” the exchange of genes between GE and non-GE crops and wild plants. One telling example is the virtually complete despoiling and disappearance of Canada’s organic canola farming industry caused by genetic contamination of its crops by GE canola introduced in 1996. Clearly, GE genes can spread uncontrollably and with unpredictable implications for agricultural sustainability and wild plant evolution.

Along with compromising the genetic makeup of conventional plant varieties and devastating organic seed stock, GE/non-GE cross-pollination can negatively affect the value of plant yields in certain markets. This was amply demonstrated in 2013 when some uncultivated GE wheat plants mysteriously appeared in a field in eastern Oregon.

Japan and Korea immediately banned some Oregon wheat imports for a few weeks, costing Oregon farmers millions of dollars. Their losses were partially recovered through a lawsuit against Monsanto, which had originally planted the GE wheat in nearby experimental fields.

Every so often, I read a cheery article about intrepid volunteers who remove non-native, invasive plants from our local ecosystems. If we continue to spread GE crops across our agricultural landscape, their progeny will inevitably be counted among those invasive plants at our ecological house.

Philip S. Wenz, who grew up in Durango and Boulder, now lives in Corvallis, Oregon, where he teaches and writes about environmental issues. www.your-ecological-house.com.