Subject: Herbicides

Expert’s Results-Driven Methodology Leads to Exclusion and Summary Judgment in Paraquat MDL

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An expert witness is not supposed to pick a desired result and then reverse engineer inputs and methods that reach that result.  As the Ninth Circuit observed 30 years ago, “[c]oming to a firm conclusion first and then doing research to support it is the antithesis of [the scientific] method.”  Claar v. Burlington Northern R.R. Co., 29 F.3d 499, 502-03 (9th Cir. 1994).  A recent opinion from the Southern District of Illinois offers a fine example of an expert with a results-driven approach and a court that called him out on it.

In re Paraquat Products Liability Litigation, 2024 WL 1659687 (S.D. Ill. Apr. 17, 2024), arises from a multidistrict litigation (“MDL”) in which the plaintiffs claim to have developed Parkinson’s disease as a result of exposure to an herbicide, paraquat.  Four plaintiffs whose cases had been chosen for the MDL’s first trials offered a statistician (the parties disputed whether he also qualified as an epidemiologist) as their sole expert to establish general causation.  He had a difficult task, as no peer-reviewed literature established a link between paraquat exposure and Parkinson’s disease.  Indeed, when the court asked the plaintiffs to identify such literature, the plaintiffs could cite only a single opinion article.  That article had been shared with another of the plaintiffs’ experts before it was published, leading the court to conclude in deciding a prior discovery dispute that there was reason to investigate “whether counsel for the MDL plaintiffs, their experts, or other third parties may have influenced the contents of the article for the benefit of one side in the MDL.”  2023 WL 8372819 (S.D. Ill. Dec. 4, 2023).

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Texas Supreme Court Refocuses on Causation and Affirms Summary Judgment in Herbicide Drift Case

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The question of whether a particular application of herbicide on one property caused damage on another’s property requires expert testimony.  When a plaintiff claims that herbicide drift caused reduced crop yields, it is not enough for an expert to opine merely that the drift caused damage to plants – the plaintiff must establish that the defendant’s application of the herbicide caused the reduced crop yield.  The distinction may sound nuanced but can have profound ramifications on litigation.  This is well illustrated in the Texas Supreme Court’s recent decision in Helena Chemical Company v. Cox, — S.W. 3d –, 2023 WL 2335694 (Tex. Mar. 3, 2023), an important and highly followed case focusing on the causation requirement in cases alleging yield loss to a crop from alleged exposure to pesticides.

The plaintiffs in Cox were cotton farmers who alleged that the defendant had supervised an aerial application of herbicide that drifted onto plaintiffs’ properties and damaged their crops, causing reduced yields.  A government inspector conducted a visual inspection of the damaged crops and claimed to find “markers” for the herbicide’s two active ingredients, but no lab testing was performed.  The inspector also identified no “consistent pattern” or “drift pattern” of crop damage over the large area encompassing the various plaintiffs’ noncontiguous properties.  Plaintiffs disclosed a slate of experts to support their allegations, but the trial court excluded the experts and granted summary judgment to the defendant.  The court of appeals reversed, finding the experts admissible despite their inability to trace the alleged drift of the herbicide in question from defendants’ application site to plaintiffs’ properties.

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