Most critical weed competition period is upto . . . . . . . . months after transplanting exist in sugarcane.

First of all the critical period of weed competition can be defined as the period between early growth during which weeds can grow without affecting crop yield and the point after which weed growth does not affect the yield. It is approximately $${\frac{1}{3}^{{\text{rd}}}}$$ of the duration of the crop. And in the case of sugarcane, it is approximately 4 months.