Mountain View Linked Herbicide to Tree Deaths

Laboratory tests confirmed imazapyr caused the decline of dozens of public trees near city landmarks.

Updated on Sept. 24, 2026 in Botany

Bold flat-color editorial illustration showing a stylized, geometric tree root ball in soil, representing environmental analysis in Mountain View. — Mountain View officials have banned the herbicide imazapyr after linking the chemical to the death of 33 public trees near the city library. AI Illustration. Upload story photo >

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Mountain View officials have identified the herbicide imazapyr as the culprit behind the death of 33 trees near the public library. The city has discontinued use of the chemical after initial investigations revealed its presence in soil and tissue samples.

Why it matters

The discovery highlights the unintended consequences of city vegetation management policies. Officials transitioned to imazapyr in 2021 to replace glyphosate, but the recent findings have forced a halt to its use as the city monitors hundreds of other potentially affected trees.

Laboratory testing confirmed the presence of imazapyr in soil and tissue samples. The city is currently monitoring 150 additional trees showing signs of deterioration following the chemical's usage since 2021.

The details

Impacted trees have been identified across Stevenson Park, Gateway Park, and medians along Castro Street, with additional removals planned at the corner of Mercy and Franklin streets. City staff have begun soil drenching in these areas to mitigate residual herbicide levels before replanting native species.

Mountain View began using imazapyr for weed control in 2021.
Trees were removed in declining condition in July 2026.
City workers cut down trees at the library during the summer of 2026.
Soil will be tested every 90 days to monitor herbicide levels.

The Big Picture

This incident follows the city's 2021 transition from glyphosate to imazapyr as an alternative for weed control. The findings contradict the anticipated benefits of the shift and require a reevaluation of chemical application methods for public vegetation.

Residents may notice ongoing remediation efforts, such as soil drenching, in public parks and along Castro Street medians. While the city plans to replant native trees, these areas will remain under observation until soil safety thresholds are met.

The takeaway

Effective urban forestry requires rigorous long-term monitoring of chemical applications near public spaces. Future planting efforts will prioritize native species once the soil is successfully cleared of residual herbicide contaminants.