There isn't a really good choice for controlling curly dock at this time. The plants have put on a substantial amount of growth already and most products are at best going to toast some of the leaves off of the plant. However, with that said here is some additional info on managing simple perennials such as curly dock:

With any herbicide program, complete control of an entire perennial root system is unlikely with one herbicide application. Follow-up applications the next season(s) are necessary to achieve the desired level of control. Controlling perennial weeds in no-till systems takes persistence.  

Controlling perennial weeds with herbicides often calls for special application methods:

•Use wipe-on applicators to apply nonselective translocated herbicides, such as glyphosate (e.g. Roundup Weathermax) to weeds taller than the crop

•Spot treat to control or suppress perennials prior to planting, in the crop, and at preharvest.

•Monitor fences rows, field borders, and other non-crop areas. Spray perennial weeds that can spread into fields.

•Remove by hand simple perennial weed such as pokeweed and curly dock. A large portion of the root or crown must be removed.

Depending upon how many curly dock weeds that you are trying to manage, either the spot treatments with Roundup in a hand sprayer or digging the individual weeds out with a shovel may be your two most effective ways of eliminating curly dock before it goes to seed again.  Also depending on how far the curly dock is in its seed development, digging them out and dropping them on the ground may not be a good practice.  If the seeds are far enough along in their development, they could still complete their development even after they are pulled out.  They may need to be carried out of the field.

Spot treating with Roundup or another glyphosate product might be very effective at this time in curly dock's development.  They should be flowering or setting seed now which means that movement of materials within the plant are going to be directed toward the roots.  This will carry the glyphosate to the roots and give a better overall kill of the entire plant.