Annual weeds are easier to control than perennials because they just live for one season and spread by seed. Perennial weeds are much harder to control because they produce seeds and also can spread by tubers, underground stems (rhizomes) or aboveground stems (stolons).

Why it is difficult to control weeds?

Weeds compete with crops for space, light, nutrients, and water. They have the ability to take up these resources much faster than crops, which will negatively affect the total yield that can be produced.

What are the most difficult weeds to control?

Perennial weeds are the most difficult to control. They spread by seed and creeping roots and if you don't pull the entire root, the plant can actually reproduce from every piece of root left behind.