I have a large mound of Brown-Eyed Susans. One plant has dried up. When I looked at it, the stems next to the ground were mushy and there was white stuff around them that resembled sawdust.
The sawdust-like substance could indicate that a critter was gnawing on the stems. This could have also led to the rot you see.
Just in case it is a disease, you should remove the affected plant, including the root and any fallen leaves, and dispose of it in a tied garbage bag.
Other than deadheading black eyed susans, is it OK to remove some of the leaves too?
Yes, you can cut the plant back further. I generally leave a few plants tall for some winter interest, but most of the plants I cut down to about 4 to 6 inches above the ground.
https://www.gardeningknowhow.com/ornamental/flowers/black-eyed-susan/black-eyed-susan-flower.htm
Why have my Black Eyed Susan plants got empty seed pods? Only one, a dark orange colour, has seed pods at the bottom of the plant, has a very few pods with seeds in of all the other plants. None have any seeds in their seed pods, and there are hundreds of empty seed pods. The plants (orange, red, and primrose yellow) have all grown very well and covered all trellises, a most stunning sight, so why have such healthy plants not got a seed in their pods? Only exception with a few seeds in some lower pods of the orange one, and even that one has masses of empty pods, so what's going on?
This could be a pollination problem. When there are flowers but no seed production, there may not be enough bees and other pollinators visiting your flowerbeds:
https://www.gardeningknowhow.com/garden-how-to/beneficial/insect-pollination-process.htm
I have a lovely black eyed Susan which has grown beautifully during the summer and I don't want to lose it. It grows on a trellis outside my house on a front wall. Shall I cover for the winter and, if so, with what? Regards, Anita.
It sounds like you have a black eyed Susan vine, since it is growing on a trellis:
This plant is not winter hardy at all, so you will need to bring the plant indoors for the winter. If this is not possible, you can take one or a few cuttings from the vine and grow them indoors, as described in the article.
Do you pinch out the tops of black eyed susie seedlings to make them produce side shoots ?
You should not need to pinch back the seedlings.
Dead heading the flowers when they are spent will help encourage more flowers and a sturdier more compact plant.
https://www.gardeningknowhow.com/ornamental/flowers/black-eyed-susan/black-eyed-susan-flower.htm
we purchased the plant in a pot which had about a 10 inch plastic trellis on it. Should remove the small plastic trellis after I transfer the plant to the ground or let the plant do it,s own thing. I have a trellis set up on a fence directly behind the plant. I am leary of handling the plant in case I damage it.
You may damage the tender vines on the plant if you try to remove the existing trellis.
I would leave it in place.
when are black eyed susans ready for cutting in Minnesota. is it aug,or sept?
Black Eyed Susan's bloom mid summer to early fall.
These plants can flower through Sept and longer.