Saving spinach: A WSU plant researcher’s work helps lucrative spinach seed industry

WSU plant pathologist Lindsey du Toit speaks about her research to stop spinach wilt Feb. 24, 2018, in her greenhouse at the university's Mount Vernon extension facility. (Rachel Alexander / The Spokesman-Review)

Lindsey du Toit is on a mission to save American spinach seeds.

Her greenhouse at Washington State University’s Mount Vernon Northwestern Washington Research and Extension Center is full of young spinach plants growing in small pots, organized in groups of 12.

Some overflow with healthy green leaves. Others are bare, with a few pins showing where spinach had briefly lived, then died.

“This grower is going to be happy,” du Toit said, pointing at healthy leaves shooting out of the pots from field 23.

Growing spinach for seeds is a fussy enterprise. The plant “bolts,” switching its growth from new leaves to flowers and seeds, only when exposed to lots of daylight. It also fares better in cooler climates, and the developing seed can be damaged by fungi if it gets wet.

Farmers plant spinach seeds in late March or early April and typically harvest by mid-May.

The plant first grows spinach leaves, then begins to flower. The leaves change shape and become more bitter, and the plant grows stalks with flower buds. Seeds develop and will eventually dry and turn brown, indicating they’re ready for harvest.

Because of the long days and climate required to grow spinach seeds, a small slice of western Washington and Oregon is the only part of the United States well-suited to producing the crop. Washington produces about one-quarter, mostly in Skagit and Snohomish counties.

And the Skagit Valley is running out of land.

The problem is a fungus called Fusarium oxysporum, which enters spinach plants through the roots and grows inside the plant’s vascular system, preventing water and nutrients from reaching the leaves. Eventually, the plant withers and dies.

Fusarium wilt, as the disease is called, has been a known problem among farmers for decades. The fix was simple, if imperfect: leave fields fallow for 15 to 20 years, and it’s usually safe to plant spinach again.

But over time, the spread of the fungus has made it hard for growers to find fresh soil.

“There used to be 3,500 to 4,000 acres of spinach seed in Skagit County and there’s closer to 2,000 now,” said Kirby Johnson, a seed farmer and president of the Puget Sound Seed Growers Association.

The acreage planted each season varies, depending on the contracts growers get with seed companies. Those companies like to spread out risk between growing regions, du Toit said, reducing the chance that a bad growing year decimates their entire seed supply.

Washington’s main competition for spinach is in Denmark, which is seeing a boom thanks to skyrocketing demand for baby spinach.

Baby leaves can be harvested as soon as 18 days after planting, du Toit said, and growers in California and Arizona can plant year-round. A typical crop takes about four million seeds per acre.

“It’s changed spinach completely as a commodity,” du Toit said.

Growers in Denmark have a major advantage: They rarely have to worry about fusarium. Because their soils are alkaline, fusarium wilt doesn’t thrive in them.

Denmark is also at a higher latitude than Washington, so it can grow some varieties of spinach that require even longer days to bolt.

To keep up, Washington growers have to work around fusarium.

It’s a challenge for many reasons. One of the biggest being that leaving a field without spinach for 15 or 20 years isn’t a guarantee that fusarium is gone.

Du Toit recalled working with a farmer once who planted a 50-acre field for spinach seed and had most of his crop die from fusarium. Forty of those acres hadn’t had spinach on them for 16 years, and the other 10 had been left for 25 years. The 10 acres were a bit healthier, but the result was catastrophic for the grower.

With an acre of spinach seed selling for $2,000 to $3,000, it’s not a gamble farmers want to take.

The WSU research center is looking at many options for stopping the fungus, including treating seeds.

Applying fungicide isn’t effective, du Toit said, because the fungus lives in the soil and is absorbed through the plant’s roots. Since water and nutrients flow from the soil to the plant, not the other way, treating the plant itself won’t kill the fungus in the soil. And treating an entire field of soil is cost-prohibitive – and can kill many helpful nutrients and organisms in the soil.

But to limit the damage in the meantime, du Toit’s answer has been soil testing, a project her lab started about a decade ago. For $200 per field, farmers can bring in a five-gallon bucket of soil before spring planting begins.

In each soil sample, du Toit and her students plant three varieties of spinach: one that’s somewhat resistant to fusarium, another, weaker variety and one in the middle. Each soil-variety combination gets four pots, which are distributed throughout the greenhouse so small differences in light and airflow affect each batch equally.

This year’s test involved 57 soil samples from Skagit Valley farmers, each from a different field.

“There’s probably $20 million of crop being assessed here,” she said.

It’s a service farmers say has helped them avoid crop failure.

“This last year I had a field I thought was probably ready for spinach and if I would not have taken that sample in to her, I probably would have plotted that field,” said Todd Johnson, a Skagit County seed grower (no relation to Kirby Johnson). Instead, he was able to move his production, avoiding a crop failure or reduced yield.

Test results can be a double-edged sword.

“It’s also made seed companies not give me a contract on a field that I’d have planted,” Kirby Johnson said. He didn’t think the results were too bad, but the company didn’t want to take the risk.

Kirby Johnson isn’t bitter about it, though. He said du Toit’s work is critical for helping Skagit Valley farmers.

“She is by far the best researcher that we’ve had here in my lifetime,” he said.

Du Toit’s latest project is evaluating spinach varieties for resistance to fusarium. She’s hoping to find solutions that will help farmers work with the disease, rather than just avoiding contaminated fields.

Fusarium is a genus of fungus that affects many other crops, including barley and bananas. It’s the pathogen behind Panama disease, the fungal wilt that wiped out Gros Michel banana plantations across Central America in the 1940s through 1960s.

The species that wilts spinach thrives in acidic soils like those in western Washington.

Hybrid spinach seeds are grown in a closed market, where farmers work under contracts with seed companies and are paid per pound of seed they produce. Farmers may have little idea how the strain they’re growing responds to disease.

“Some growers don’t know how susceptible their lines are,” du Toit said.

In the Skagit Valley, the growers and seed companies have a regional meeting in March where everyone maps out their fields. To avoid genetic drift and contamination, plots of different spinach varieties must have at least a mile between them, Kirby Johnson said.

Seed companies give farmers the seeds they’re going to grow. Breeding varieties that are resistent to fusarium hasn’t been a priority, du Toit said, because seed companies have so many other things they need to breed for: resistance to diseases common in the California spinach fields, deep green color and transportability.

“Historically, there hasn’t been a need to breed for it,” du Toit said.

Her second greenhouse tests new lines of spinach by growing them in soil with various degrees of fusarium contamination. Some varieties do well in all three soil samples, while others wither and die in the fusarium-rich mix.

Seed companies bring her lines they want to test and pay $75 for each variety. She said it’s not uncommon to hear that spinach varieties she’s working with are still under development.

Todd Johnson said he’s hopeful her work could lead to spinach seeds that are more resistant to the wilt. That could mean farmers don’t have to wait quite as long between spinach crops, freeing up land to keep baby spinach on the table.

“If we could get down to an 8- or 10-year rotation, I think we would be in great shape,” he said.