Blocking sunlight from native species of plants, competing for soil moisture, competing for nutrients, and producing a chemical that inhibits other plant growth.
To control the plant there are different solutions depending on the severity of the situation. If the plant is still small hand-pulling is effective. Once the plant has reached adult hood then there are two solutions to choose from. One is the cut-stump method which involves cutting the plant off at its stump. The other is spraying either folier spray or basil-bark method.