It depends on the weed. Overall you’re going to put pressure on it. With conventional fields like the ones pictured in this article, there’s often no ground cover. If you have a ground cover (say, clover) and you’re defoliating the weeds all the time, then you have a chance.

But some weeds, like invasive blackberries here in the Pacific Northwest, are extremely resilient and will shrug off defoliation.

Thanks for the info!

> But some weeds, like invasive blackberries here in the Pacific Northwest, are extremely resilient and will shrug off defoliation.

How does that work? I thought all plants (by definition?) need photosynthesis to stay alive in non-dormant states.

Do blackberry plants have some way of getting energy other than photosynthesis in their leaves?

Invasive European blackberries can also draw energy directly from the anger of gardeners vainly attempting to remove them.

If you keep cutting it off and have control over its whole potential growing area it will eventually die. It has some scary properties like roots that travel 20 feet easily and spring up a new independent plant and a insane growth rate once it sprouts. If it’s out of control you probably need someone to first destroy the hedge with a flamethrower

They grow these enormous and very resilient root balls under ground. I was taught that the most efficient way to kill a blackberry bush was to remove the structure above ground, locate a central stalk that leads under ground, and stick the end in kerosene or gasoline I don't remember which. That gets sucked up into the root ball and kills the plant. Never done it myself, mind.

Sure that is a one-stop permanent solution for a plant which grows back its leaves very quickly but the question is, how can the plant thrive enough to harm other crops if you defoliate it every day?

What? I'm telling an anecdote about blackberries over here. It's not commentary on the broader topic.

If the crop is near a bush, then the plant can happily grow in the bush and send roots to the crop.

I’m not a botanist but my understanding is that the root balls hold a ton of energy and the plant can just keep sending out shoots, and spread underground for fairly long distances. So, eventually that energy source will run out, but they’re invasive because of how resilient they are at finding sneaky ways to hide and appear.

> I thought all plants (by definition?) need photosynthesis to stay alive in non-dormant states.

There are parasitic plants that don't photosynthesize at all, like the Monotropoideae and Rafflesiaceae.

Among photosynthesizing plants, rhubarb can be "forced" (grown in complete darkness to reduce bitterness and get an earlier harvest), and potatoes can sprout if left in the pantry for too long.