Poison sumac is one of the unusual plants in that it is honestly pretty; it turns a gorgeous crimson in the fall, yet it causes rashes in people who are susceptible. Worst of all, it has a very strong, wide spread, and deep root system, which makes it difficult using normal means to eradicate.
Many people have struggled for hours in the summer sun, suitably clothed in long sleeve shirts, pants, and gloves to prevent skin irritation, in attempt to dig poison sumac up. The problem is that the plant is so hardy that if any of the roots are left behind, they will simply send up a new poison sumac plant.
Commercial herbicides don't provide a very good answer, either. Not only do they tend to kill every plant in the area when used at the strength necessarily to kill poison sumac, but also they also usually don't get to the deep roots when mixed and applied according to package instructions in surface treatments.
It would seem that the only choice would be to let the plant grow, which is no solution at all. Luckily, there is a surprisingly easy way to get rid of poison sumac. It even works for problem blackberry bushes, poison oak, and poison ivy. Note that since poison sumac can seed itself, this may need to be repeated several times a year for a couple years before it is entirely removed.
Special note of caution: Some people are extremely allergic to poison sumac, poison oak, and poison ivy. In the case of such extreme allergies, it is neither safe nor wise to work with these plants at all.
For those who aren't badly allergic, begin with the following supplies:
1 sharp pair of pruning sheers
1 pair of good rubber gloves (they must be fairly thick)
1 empty 3-pound coffee can (do not use plastic)
1 pint of diesel fuel
1 pint of commercial vegetation killer (2-4-D or a product containing 2-4-D is preferable, but is becoming much harder to find in most places)
Carefully mix the vegetation killer with the diesel in the coffee can. Vegetation killer is toxic, and diesel is a solvent, so take care to avoid splashes or contact with the skin.
Immediately clip the poison sumac or other plants you are trying to kill, to within a couple inches of the ground. Dip the brush in the poison mixture and liberally brush the fluid on the fresh cut, coating the cut completely.
The gloves, can, brush, and mixture should be discarded after treating the poison sumac.
What happens is this: The diesel, which again is a solvent, acts to suspend the poison. It functions to deliver the poison to the deepest roots by reverse capillary action. In other words, it soaks in through the cut in the plant and is drawn into the roots. The diesel isn't the killing agent, the herbicide is, but the diesel allows the poison to reach all the roots. This would not be possible with normal surface treatment.
Within a week or two, the sumac will be dead.
Remember though that seeds in the ground will still germinate and grow into more sumac plants, which is why the procedure should be repeated. The branches and limbs that are trimmed should also not be burned as the smoke can carry the poisons in the sumac and can cause allergic reactions in the people who breathe the smoke. Instead, bury them where they can decompose naturally.
Using this method will remove poison sumac and other hard to kill but unwanted plants, while causing minimal damage to other plants in the vicinity. Care must be taken when using this method, however if you want to get rid of poison sumac and don't want to spend hours of fruitless and back breaking digging to do it, this will get the job done.