Salinas Valley Agriculture

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INSV negative lettuce leaves arranged side by side with brown spot symptoms on midribs.

Cause of lettuce midrib spotting symptoms is still inconclusive

August 18, 2026
By Nicholas E Clark, Yu-Chen Wang
  In early July, a pest control adviser (PCA) brought samples of romaine lettuce to the UC Cooperative Extension office of Monterey County in Salinas. The lettuce was from a couple of fields in Gonzales nearing harvest. The PCA was concerned about blemishes on the leaf midribs that appeared as…
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