All weeds are created equal, right? Wrong. Some weeds are hardly troublesome while others cause huge problems for farmers, yield, machinery and more.

If you’re wondering which weeds are which, keep reading: The Weed Science Society of America has updated the definitions for the four—yes, four—different types of weeds.

Here they are:

Weed. “A plant that causes economic losses or ecological damages, creates health problems for humans or animals or is undesirable where is it growing.” Think crabgrass, giant foxtail or common lambsquarters, for example.

Noxious weed. “Any plant designated by federal, state or local government officials as injurious to public health, agriculture, recreate, wildlife or property. Once a weed is classified as noxious authorities can implement quarantines and take other actions to contain or destroy the weed and limit its spread.” For example, purple loosestrife, hydrilla and witchweed are all noxious weeds. There are over 100 weeds on the Federal Noxious Weed list.

Invasive weed. “Weeds that establish, persist and spread widely in natural ecosystems outside the plant’s native range. When in a foreign environment, these invaders often lack natural enemies to curtail their growth, which allows them to overrun native plants and ecosystems.” Examples of invasive weeds include tree-of-heaven, tamarisk and downy brome (cheatgrass). Many invasive weeds are also classified as noxious.

Superweed. “In addition to the science-based definitions above, many people use the slang term ‘superweed’ to describe weeds that have evolved characteristics that make them more difficult to manage as a result of repeated use of the same weed management tactic. The most common use of the slang refers to a weed that has become resistant to one or more herbicide mechanisms of action after their repeated use in the absence of more diverse weed control measures.” Click here for a comprehensive list of herbicide resistant superweeds.

As farmers know, weeds are bad news. Follow best management practices to make sure you beat these yield robbers, whether they are just weeds, noxious, invasive, or “super,” in your fields.