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A borer type insect is likely the cause.

I would remove the plant and dispose of the material.

You can treat the soil with an insecticide.

https://www.gardeningknowhow.com/plant-problems/pests/insects/crown-borer-management.htm

It depends on the variety. Some varieties should be red when harvested, while others should be harvested when green because the stalks never turn red. If you have a red variety, wait until the stalks are red to harvest. After harvesting, you can trim the plants back or leave them alone until after winter. Here is an article that you may find helpful: https://www.gardeningknowhow.com/edible/vegetables/rhubarb/harvesting-rhubarb.htm

If you plan on harvesting, then yes, do so before winter--even fall. It is not usually a good idea to harvest this late in the season as it may cause the plant to go into a late season growth spurt, which opens it up to damage. It will use up energy it will need for the winter and may not be able to last through the winter due to this.

Let the stalks die down naturally, when they have perished in the first frost or two, remove them.
You can add a touch of mulch to the plant and crown to add some winter protection.
In my zone 4 garden I don't mulch and have no issues with my plants surviving in a sheltered location.

https://www.gardeningknowhow.com/edible/vegetables/rhubarb/protecting-rhubarb-in-winter.htm

Generally I like to see some of the leaves left on the plant to help feed the plant.
Rhubarb is generally quite hardy and your plant likely will regrow in spring.

https://www.gardeningknowhow.com/edible/vegetables/rhubarb/protecting-rhubarb-in-winter.htm

It appears that you have Rhubarb growing in your garden.

Here are some links with more information.
https://www.gardeningknowhow.com/edible/vegetables/rhubarb/grow-rhubarb.htm
https://www.gardeningknowhow.com/edible/vegetables/rhubarb/harvesting-rhubarb.htm