C. orbiculatus is a serious invasive weed in much of eastern North America.

It has become a serious invasive weed in many areas of Europe and North America, after being introduced as a garden plant.

The bulletin says that a "potentially serious weed" has arrived in Westchester.

All of Leucas species is becoming a serious weed in rice fields, sugarcane and banana plantation.

Black nightshade can be a serious agricultural weed when it competes with crops.

It can be a serious weed of rice cultivation in Asia.

The species is naturalised in Hawaii, and regarded as a serious weed there.

Azolla are also serious weeds in many parts of the world, entirely covering some bodies of water.

It is one of the most serious weeds of agricultural fields in temperate regions of the world.

In crop fields where group 2 herbicides have been repeatedly used this plant can become a serious and damaging weed.