Shares of Newport Beach-based American Vanguard Corp. rose by more than 8% to a market value of about $341 million on a recent court decision that clears it for sales of a fungicide.

The boost for the maker of agricultural and specialty chemicals came on a decision by the United States District Court for the District of Columbia to void a “Stop Sale, Use or Removal Order” issued in August 2010 by the United States Environmental Protection Agency.

The order affected sales of the pentacholoronitrobenzene (PCNB) product line by wholly-owned subsidiary Amvac Chemical Corp.

The EPA contended that American Vanguard does not identify trace impurities in lists of ingredients for new pesticide or chemical formulations.

American Vanguard challenged the regulatory agency’s move, citing denial of due process.

The court found that the EPA official who signed order lacked authority to do so.

The case has been sent back to the EPA for reconsideration.