Weeds and Parasitism.?

Question

Would you consider weeds to be parasitic?

I think some species are parasitic, but is large crabgrass (scientific name Digitaria sanguinalis) parasitic?

Thank You!

Answer 1

Since crab grass spreads by root and will grow anywhere I would not consider this parasitic. It does not depend on other plants for life. It is aggressive though.

Answer 2

Yes, some weeds are truly parasitic, in that they directly attack other plants and deprive them of water, nutrients, etc.  

There are two kinds: the total parasite and the partial parasites.   I don't know whether carbgrass is partially or totally parasitic; it's a question for the exerts.  

Answer 3

Yes, because they are feeding off of their host and taking their nutrients (ex. weeds in my garden cause my tomato plants to stay small)

Answer 4

Most weeds wouldn't be parasitic in the classic definition, but rather sucessful competitors.  Since weeds do not operate by attaching to or internally invading a host, they are not really parasitic.  By outcompeting other plants for water and nutrients, they hurt plants around them, but not truly in a parasitic way.  The exception would be epiphytes which literally attach to their host and suck nutrients from them.