Biological invasions became one of the most prominent ecological issues on earth in the middle of the 21st century. Although there were many troublesome pests such as gypsy moths and fire ants, runaway flora was vastly more invasive.
Several species upset the balance by attacking other helpful plants. Autumn olive ruthlessly eliminated other species. Black locust, toxic to any, could grow 30-90 feet. With a 2-4 foot trunk diameter, it eliminated diversity in the remaining forests by hoarding the sunlight.
Multiflora rose created dense thickets which were particularly destructive to pastureland because it replaced many of the forage plants needed by the scarce livestock. The farming industry faced other problems, such as white snakeroot which caused any livestock which consumed it to produce milk fatal to humans. Stinging nettle ran rampant during the green sky era and so did highly flammable cheat grass, which was easily ignited in the intense heat to create large, uncontrolled fires. Garlic mustard took over all the ground leaves.
However, above all these lurked one prolific, heinous green menace. The fast-growing highly invasive kudzu vine constantly battled with humanity to reclaim structures and farmland. So troublesome was the kudzu vine that Thayer Corp created spot-fire treatment teams (like Mack Willis') to deal with the leafy scourge.