Warfare Waged by Canada thistle

•  Barricades: Sharp prickles on leaves supply it with mechanical protection to provide a barrier to prevent grazing and discourage pulling. Grazers instead devour its nearby competitors and free up more territory for Canada thistle to occupy.

•  The Underground: It deploys vertical perennial roots 4- 9’, to even 23’ that support up to 18’ of extensive lateral roots that generate new plant clones every 2-6”! New plant clones declare their own independence of the parent plant after 2 years and grow additional 20’ colonies until colonies reach up to 100’ around in 3 years. Root pieces as small as ¼” x 1/8” survive to fight again with new shoots in 5-15 days or survive 100 days without additional photosynthesis. Mowing or cutting down the parent plant simply mobilizes new buds into militant action.

•  Timing strategies: staggered growth stages occur at the same time, which also aids its overthrow of the Old Guard.

•  Battalions of seed dispersal forces: Each seed has a hard seedcase, “achene”, its own armor. A “pappus”, or fluffy parachute with tiny hooked cells, tops the achene to fly ½ mile to bombard new territory, like an air force. Airborne Goldfinches and Sparrows eat seeds, launch them into flight and use fluffy seeds as down for nests. Seeds endure water and help it launch naval attacks. Seeds also hitchhike rides on ground-force troops: such as small mammals, the hooves of large animals, or people who stow it away in ballast, in hay, on shoes, under garden equipment or other vehicles.

•  Endless reinforcements: by hardy perennial seeds and vigorous seedlings. One plant produces up to 40,000-60,000 seeds that last in the soil seedbank for 21 years or more. Seeds germinate from ½”-3” under ground and with deeper burial, they even survive longer. Flowers outcross and activate its potential for genetic diversity, plasticity, and adaptation. After pollination, seeds form within 10 days. Flowers also self-pollinate.

•  Surprise attack by alien invaders: it arrived here with no biocontrols to keep it in check. It debilitates native biodiversity.

•  Biological warfare: hosts diseases for other plants.

•  Chemical warfare: it’s “allelopathic”, that is, it emits chemicals that inhibit other crops. It sends out the chemical cnicin which reduces yield 80% in Corn, 95% in Soybean, 60% in Wheat and native Grass forage.

•  Attack on food supplies: high nitrate levels can distress or kill grazers.

•  It enlists human assistance: Its pretty, fragrant flowers offer it protection from uncertain gardeners. People assist its spread even more as bird watchers, butterfly gardeners, and bee keepers keep some of these turncoats around.

While it overwinters better than Napoleon’s armies did in Russia, it can’t make it in the South. If you use bio-controls, mow, pull and smother it, or improve soil fertility and moisture levels, and if you repeat these multi-pronged methods of attack on Canada thistle 3 times a season for a few years, you can thwart it.

Wetlands invaders

Floods destroy plants that require specific water conditions, clear a competitive path for floodplain survivors, and give the flood-adapted seeds the required type of watery wake-up call that other plants cannot answer. Enter Common reed, Phragmites australis, a powerful wetland raider. It probably arrived in ship ballast in the 1800s and may have been brought intentionally. After all, it has its uses. Dry stalks can be used for construction, pen quills, shafts of arrows, mats, cigarette paper, and regular paper. The whole plant provides edible food, its seeds provide a wholesome grain.