Risky Business

Carol Miles
WSU Plant Pathologist Lindsey du Toit (center), graduate student Shannon Carmody (left) and Sakata Seed America representative Kathy Lindbloom (right) discuss the results of this year’s soil testing that show different levels of risk for Spinach Fusarium wilt disease. (Photo by Kim Binczewski)

Soil test results help spinach seed growers identify best spots for spring planting.

Nearly two dozen spinach seed growers got a heads-up on which local fields may be most conducive to yielding a healthy crop this year, as a result of a WSU Spinach Fusarium Wilt Soil Bioassay Open House held here February 19.

Example of a high-risk soil shows pins indicating dead or dying spinach plants.  (Photo courtesy of Lindsey du Toit)

Hosted by WSU Plant Pathologist Lindsey du Toit and her WSU Mount Vernon vegetable seed pathology research team, the annual open house was the result of a two-month soil assessment aimed at determining the risk of the disease Spinach Fusarium wilt in commercial fields being considered for this spring’s spinach seed crop plantings.

The timing of the open house allows growers to work with seed companies in identifying their top field choices for spinach seed crop locations prior to the March 2 pinning meeting, when 2015 planting sites will be designated by random drawing, du Toit said.

In the past six years, 200 fields have been tested in Whatcom, Skagit, Snohomish, Island and Clallam counties.
This year, 29 growers brought in samples from 30 fields in this region, where soils are notorious for fostering Spinach Fusarium wilt, which can cause severe economic losses — including leaf wilt, stunting, root necrosis, reduced seed yield, and even total crop failure – in a spinach seed crop. The fungus that causes Fusarium wilt, Fusarium oxysporum f. sp.spinaciae, is able to survive 10-15 years in soil — even when spinach is not present.

Spinach plants thriving in a soil with very low risk of Fusarium wilt.  (Photo courtesy of Lindsey du Toit)

For comparison, plots made from the field soils were each planted with three parent spinach lines, ranging from highly susceptible to partially resistant to Fusarium wilt. Results displayed at the open house made it visually clear which of the tested fields can be safely planted to spinach.

Nineteen of the 30 fields – represented by soil plots full of vibrant, leafy, green samples — were identified as low risk for harboring the disease.  So even if a line of spinach susceptible to Fusarium wilt is planted, chances are the resulting crop will be productive, du Toit said.

“The more important results were which fields should not be planted to spinach seed crops because of a high risk of Fusarium wilt,” she added. “Four fields received that designation and will likely not be planted to spinach seed crops in 2015.”

Those field samples yielded soil plots with sparse, yellow, dying spinach plants.

“The contrast is remarkable,” said first-time spinach Marty Galbreath of Burlington’s Lazy J Farm.  “It’s great for growers to know what’s happening in the soil before we invest all our resources in the field.  If you didn’t know, you could end up losing your whole crop – just like that.”