The Fourth Circuit tells us:

Generally speaking, chemical crabgrass control products are most effective when applied to “pre-emergent” crabgrass . . . the products are also effective on early “post-emergent” crabgrass but are ineffective when applied to mature crabgrass plants . . .   Scotts [plaintiff] contends that the Vigoro [defendant] package misleads consumers into believing that Vigoro can kill mature crabgrass.

editor’s note – I have found that doing nothing until the first frost kills the crabgrass is effective.

This is about depicting mature crabgrass on the crabgrass killer package.  Scotts has apparently been in and out of court over the Vigoro packaging which looks something like this.  Scotts argues that because the product only kills crabgrass up to four weeks old, rather than the mature crabgrass depicted on the bag, the graphic conveys the literally false message that Vigoro is capable of killing mature crabgrass.  This sounds a little suspect (I mean are they going to depict crabgrass roots on the package?) until you hear that Scotts came up wth survey evidence that 92.5%  of the respondents understood the package to mean that.  This impressed the District Court.

However, the Circuit Court threw the survey into the dustbins of expensive surveys given zero weight due to faulty methodology.  Scotts also wasn’t able to show that Vigoro intentionally set out to deceive anyone into thinking it could kill mature crabgrass.  Hit the remand button.

Scotts v. United Industrial, 65 USPQ2d 1161, no. 02-1738 (4th Cir. Dec 23, 2002).