Lettuce Virus Resurfaces in Salinas Valley

Researchers record higher case numbers of impatiens necrotic spot virus in 2025 after two years of lower levels.

Published on Feb. 25, 2026

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After two years of lower levels of impatiens necrotic spot virus (INSV) in the Salinas Valley, researchers have recorded a higher number of cases during the 2025 season, though they say INSV did not reach the widespread levels seen in 2022, when the virus led to substantial yield losses, short supplies of lettuce and record-high prices.

Why it matters

INSV is a serious threat to lettuce crops in the Salinas Valley, as it can cause stunting, yellowing, wilting, and distorted leaves, leading to unmarketable heads. The virus is spread primarily by western flower thrips, which are difficult to control, making INSV outbreaks challenging for farmers to manage.

The details

INSV was first documented in Monterey County lettuce in 2006, with minor to severe isolated outbreaks in the ensuing years. The growing seasons from 2018 through 2022 were particularly brutal, with up to 100% crop losses in some fields. While there was a reprieve in 2023 and 2024 due to extensive rains, flooding, and cold weather, thrips numbers and INSV infections appear to be higher in 2025, especially in the fall.

  • INSV was first documented in Monterey County lettuce in 2006.
  • Severe INSV outbreaks occurred in the Salinas Valley from 2018 to 2022.
  • There was a reprieve from INSV in 2023 and 2024 due to extensive rains, flooding, and cold weather.
  • INSV cases increased again in 2025, with a spike in infections later in the summer.

The players

Daniel Hasegawa

A research entomologist for the U.S. Department of Agriculture who observed a few localized outbreaks of INSV early in the 2025 season and a spike in cases later in the summer.

Richard Smith

A retired University of California Cooperative Extension (UCCE) vegetable crops adviser who has studied INSV extensively.

Mark Mason

The manager of Huntington Farms in Soledad, whose 2025 harvest of more than 4,000 acres of head, romaine and leaf lettuce and endive was decent, despite INSV showing up late in the season.

Yu-Chen Wang

The UCCE plant pathology adviser for Monterey, Santa Cruz and San Benito counties, who said virus levels accumulated in 2025, though not as bad as in 2018 to 2022.

Jennifer Clarke

The executive director of the California Leafy Greens Research Board, who said the group will likely focus more of its research on INSV.

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What they’re saying

“I think we've been dodging the bullet the past few years, but it looks like whatever guardrails that existed are breaking down.”

— Richard Smith, retired UCCE vegetable crops adviser (Salinas Valley Tribune)

“You can't spray your way out of this one, which makes it so complicated.”

— Richard Smith, retired UCCE vegetable crops adviser (Salinas Valley Tribune)

“(Hasegawa) and I saw 40-acre fields just wiped out. The whole thing was gone.”

— Richard Smith, retired UCCE vegetable crops adviser (Salinas Valley Tribune)

“(2025) was a good year until September into October. We caught the symptoms at the end of the harvest, but overall, it was OK. We had some fields that were clean and some that were 40% losses.”

— Mark Mason, manager of Huntington Farms (Salinas Valley Tribune)

“The 2025 harvest is not as bad, but that's a matter of perspective. The last few years haven't been as disastrous. Maybe the shock factor is no longer there.”

— Jennifer Clarke, executive director of the California Leafy Greens Research Board (Salinas Valley Tribune)

What’s next

University of California Cooperative Extension entomology adviser Dylan Beal and U.S. Department of Agriculture research entomologist Daniel Hasegawa will continue to monitor the situation and work with farmers to develop new strategies for controlling the spread of INSV.

The takeaway

The resurgence of impatiens necrotic spot virus in the Salinas Valley highlights the ongoing challenge for lettuce growers in the region. While the 2025 season was not as severe as the previous five years, the virus remains a persistent threat that requires diligent weed management, research into resistant crop varieties, and the development of new control methods to protect this vital agricultural region.