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.

The Texas Supreme Court began by upholding and clarifying its prior precedent in holding that:

“[T]he ultimate issue . . . in a toxic tort case . . . is always specific causation—whether the defendant’s product caused the plaintiff’s injury.” Bostic v. Georgia-Pacific Corp., 439 S.W.3d 332, 351 (Tex. 2014). It is important to emphasize at the outset that the plaintiffs’ injury here is not “damage” to cotton plants, such as wilted leaves. Instead, the injury for which the plaintiffs seek recovery is a financial one—decreased revenue from a reduced yield of cotton at harvest. It is therefore not enough for the plaintiffs to show that drifting herbicides reached their plants and “damaged” them in some way. Instead, they must show that Helena’s application of Sendero caused their plants to yield less cotton at harvest.

The Court held that in order to satisfy this burden, it is not enough to merely claim that any exposure can harm the crop.  In other words, visual symptoms in response to alleged exposure is insufficient.  Instead, a plaintiff must show what amount of the alleged pesticide reached the crop, and whether that amount would substantially contribute to the claimed lost crop yields.  In doing so, “there must be reliable evidence ruling out other plausible alternative causes.”

In Cox, the Court noted two plausible alternative causes – weather and other herbicides – and noted that none of plaintiffs’ experts had accounted for the possible effect of weather on the reduced crop yields at all.  This was particularly problematic in that many of the plaintiffs had applied for insurance benefits for losses caused by weather.  The Court also noted that the record supported application of numerous other herbicides in the area as well as an application of the herbicide in question by actors other than defendant.  Although two of plaintiffs’ experts opined that defendant’s application was the only one large enough to cause the “heavy losses” alleged by plaintiffs, the Court held that “this approach largely assumes the matter to be proved.”  Because the experts’ reasoning depended on the unproven assumption that the reduced crop yields were all caused by a single source – notwithstanding the experts’ failure to address weather-related losses – their reasoning amounted to their mere say-so and was excluded.

The Court also noted that, at least in this case, lay opinions of the farmers themselves were not sufficient.  Because “[d]etermining whether a particular application of aerial herbicide substantially contributed to the failure of crops miles away requires knowledge and analysis of scientific matters beyond the competence of laymen,” expert testimony was required.

Additionally, in dealing with plaintiff’s burden of showing “whether it [was] the defendant’s product,” the Court noted that positive test samples showing the active ingredient may not carry the day if there is evidence of multiple products containing the same active ingredient being used in the geographic vicinity.

Finally, while the Court did not go so far as to explicitly require field-by-field (USDA fields)-level causation, it made clear that a “plaintiff must show causation for the entire area for which he seeks recovery, and using USDA’s field designations may be a useful way to do so.”

In summary, the Cox decision reinforced that traditional causation determinations applied in cases alleging yield loss to a crop from alleged exposure to pesticides, and that plaintiffs would be required to meet their burdens with reliable and admissible expert testimony based on sufficient evidence and data.