Topcane 700 WG uptake is via roots. Topcane 700 WG works through the inhibition of photosystem II. This is by the destruction of chlorophyll and carotenoids leading to chlorosis (yellowing), and the formation of free radicals that destroy cell membranes, causing necrosis and death. The herbicide does not prevent the emergence of weeds, but action is manifested once the plant begins to rely on photosynthesis. Symptoms appear first on older bigger leaves that consume more water. The spectrum of activity.