Front Hub Wheel Falling off
Yes - one or two torque arms will help.   Otherwise all the impulse is being send through your dropouts, which will be steel and will flex.   This undoes the wheel nuts over time.   This also fretts out the dropouts whih will cost you a new fork.

Do you have anti-rotation washers in the fork dropouts too?  Even my 250W motor needed them.

More info:


From http://www.ebikeschool.com/torque-arm-need-one/