Gallium mollugo

Smooth bedstraw is a perennial plant with many, upright, square stems. These stems can be 25 to 120 cm (10 to 48 inches) long and tend to be weak. It is able to reproduce by seed and underground stems, contributing to the clumped growth habit. The entire plant is smooth to the touch and this fact is one distinction between smooth bedstraw and a related species, cleavers or rough bedstraw

Smooth bedstraw is particularly difficult to control in forage crops, especially if desirable forage legumes are present. Management is easier before the plant is fully established in the field, so crop scouting and spot control applications around field margins is key to avoid weed movement into a field area
https://www2.gnb.ca/content/dam/gnb/Departments/10/pdf/Agriculture/FieldCrops-GrandesCultures/SmoothBedstraw.pdf