Neck openings and tunic bottoms which have placket openings tend to roll unless an edging is added. There are times, though when you want a simple clean line and an edging is just not what you want. Here are a few methods to prevent roll on your placket edges.
1. Set aside several yards of your yarn before you start knitting. Using the separate length of yarn, e-wrap over the last 5 needles opposite the carriage. Knit 1 row. Using another length of yarn on the other side of the knit piece, e-wrap over the last 5 needles opposite the carriage. Knit 1 row. Continue to add the e-wrap to the end needles alternating each side every row until you reach the end of your placket.
2. If you have a ribber, you can set your main bed and ribber needles at the two edges of your knit piece for full needle rib. That would be the 5 edge needles on either side of the main bed and only the corresponding 5 needles on the ribber. Knit to the desired length of the placket. Check your machine ribber manual for full needle set-up.