Zizia aureus fall regrowth

Right now Zizia aureus (golden Alexanders) is showing lush growth throughout our open savannas. Fall regrowth like this is fairly common.

Fall regrowth is an interesting ecological phenomenon. I assume this works as follows:

• Since Zizia is a species that shows up early in the spring, it does best in cooler weather.
• It flowers, sets seed, and dies back by early August, but the root stock is still alive.
• When the weather turns cool again, new buds grow and form leaves.
• The leaves photosynthesize and translocate carbohydrates to the roots.
• When winter comes, the above-ground portions die back, but the roots remain alive.
• Spring growth starts early, as soon as the soil starts to warm up. The energy in the roots from the fall process gives the plants a head start. 
• Flower buds start to show in early April.
• The whole cycle continues through another year.

There are lots of "bad" plants that exhibit fall regrowth, and probably carry out this same cycle. One of the most serious is garlic mustard, but others are reed canary grass, bluegrass, motherwort, and mullein.

Incidentally, right now is an excellent time to spray any bad plants using glyphosate. Most of the native plants have senesced and will not be affected, whereas the green leaves of the weeds will absorb the herbicide and translocate it to the roots. The only problem is to avoid spraying any good plans such as Zizia.