There are poorly-soluble compounds that become trapped in the upper layers of the soil. They are absorbed through the roots, and act by inhibiting photosynthesis in young seedlings. They are best applied before budburst on weed-free soils (weed-shadow effect). The higher the clay content of the soil, the less they are leached, and so the less risk there is to the vine.
They are slowly broken down by micro-organisms, but their effect can last several months. Prolonged use can cause problems in re-plantations.

The only residuals approved in the UK are Isoxaben (FLEXIDOR) and propyzamide (KERB), though Oxadiazon (RONSTAR) does have some residual effect.Simazine used to be used, but there is now too much resistance to it, so its approval has been withdrawn.