USDA APHIS has advised:

• Vietnam will require destruction or reexport of U.S. wheat or soybeans in which seeds of Canada thistle (Cirsium arvense) are detected in incoming deliveries arriving March 1, 2019 or later. APHIS will implement a Canada thistle sampling protocol during U.S. export phytosanitary inspection for wheat and soybeans after an expected directive is issued by the Federal Grain Inspection Service. Only consignments in which no Canada thistle seed is detected will be eligible for phytosanitary certification for Vietnam
• FGIS will issue a new directive by Wednesday, February 27, which will describe the procedures for detecting Canada thistle (Cirsium arvense) seeds in wheat and soybeans bound for Vietnam. All wheat and soybean consignments with inspection dates on or after the directive date will require seed analysis. APHIS will issue phytosanitary certificates for wheat and soybeans bound for Vietnam inspected on or after the directive date only when accompanied by a completed export phytosanitary inspection report (e.g. FGIS-921-2) indicating freedom from seed of Canada thistle. The FGIS directive is to be posted at: https://www.ams.usda.gov/about-ams/fgis-program-directives.

NAEGA continues pursue measures based on sound science and consistent with international convention that are least trade distortive. We are working to support  work with VN PPD in order to establish a compliance regime to pre-empt the precautionary and yet-to-be-identified-or-justified visual inspection at import and re-export measures upon port arrival of U.S. cargoes in VN.   We are also filing detailed and updated reporting, including discussion actions exporters as well as NAEGA might take.  Reports can be found here.