Question

how weeds effect with crop plants?

Answer 1

Weeds are the unwanted plants growing along with the crop it's shows negative effects to the plants ! for killing weeds we needs weedicides

Answer 2

Weeds are unwanted plants that grow in crop plant. Weed which grow with plants directly effect their nutrition due to which crop is not good.Some weeds also destroys some crops.
Some weeds are also good for plants
In older days when there was no fertilizer
People used to plant weed with crops which protected it from insects