Cottonwood (Populus deltoides)
DESCRIPTIONS
Cottonwood: A close relative of the willow, the eastern cottonwood shares some of its characteristics. Also a dioecious plant, it bares pistils and stamens in catkins, although its catkins tend to droop, whereas willow catkins are normally upright or spreading. Its fruit is a 2-4-valved capsule. The cottonwood grows only as a tree, with spreading branches and a tall crown reaching heights of over 100 feet. Multi-stemmed cottonwoods may reach diameters of over 10 feet. The tree bark is nearly black, deeply furrowed, and decorated with resinous, many-scaled leaf buds in winter. Leaves are simple and alternately arranged on the stems. Cottonwood leaves have broad, flat bases that taper to a point near the tips. Leaf margins are deeply serrate and often curve inward towards the centermost veins of their blades.
DISTRIBUTION AND HABITAT
Cottonwood: This native tree ranges from Quebec and New England to Florida, and west to the base of the Rocky Mountains. Like the willow, cottonwood prefers forested wetlands, and flourishes in riparian and flood plain habitats; it generally occupies low woods, moist prairies, and river banks. It can be found along streams and ditches, around the edges of ponds, and in almost any damp depression, whether natural or man-made.
LIFE HISTORY AND EFFECTS OF INVASION
Willow and Cottonwood: Female flowers of the willow and cottonwood are pollinated in the springtime, giving rise to many-seeded capsules that ripen between early summer and late fall. The seeds are usually dispersed by wind and water. Asexual reproduction can take place by suckers, sprouts, and root shoots. Saplings flourish in damp, well-lit areas. Cottonwood and willow are shade-intolerant, and do not compete well under dense forest canopies. Some willows and cottonwood are occasionally considered problem plants that alter wetlands by limiting herbaceous undergrowth. Once in the sapling stage, these woody plants are difficult to eradicate.
CONTROLLING WILLOW, COTTONWOOD, BOXELDER, AND DOGWOOD
When choosing a control strategy for willow, cottonwood, boxelder, or dogwood, it is important that the habitat manager carefully observe the life-history responses of the trees or shrubs within the target region, because responses may vary from region to region, affecting the success of management manipulations. For instance, in northerly regions, willow can be controlled by mowing seedlings and saplings and subsequent flooding; farther south, mowing and flooding may actually induce more aggressive plant growth.
Mechanical Methods: The complete drawdown of water in an impoundment during the hottest summer days may prevent the establishment of extensive root systems by woody plant seedlings. Combined with discing, drawdown can terminate newly established seedlings and destroy the root systems of older plants. It should be noted that in southern latitudes, woody species of plants may experience an enhanced germination rate if drawdowns expose great expanses of mud flats before seed dispersal; exposing mud flats after seed dispersal can reduce and confine establishment of woody plant growth.
Discing is an economical technique that can destroy both aerial and subterranean woody plant growth. A double cross-disc is most effective for disturbing especially dense stands of trees and shrubs. Discing 2-3 times during the growing season is the best method to impair seedling growth. Discing becomes ineffective when plant stems reach more than three inches in diameter. After plants reach four inches in diameter, bulldozing is the only feasible method to physically remove them from the landscape en masse. The method is rarely advised due to the obvious resulting alteration of wetland topography.
Cottonwood can be eradicated through girdling. Boxelder, however, is resistant to girdling and sends up multiple shoots below the point where its phloem is severed. Large-diameter trees can be removed with a chainsaw. Resprouts must be recut, or herbicides may be applied to the cut stump (see below).
Chemical Control: Because new shoots may sprout from severed trunks, cut stems and stumps must be treated with an herbicide, such as glyphosate licensed for use in wetland environments.
Glyphosate applied to foliage at 7pts/acre in August has been found to kill dogwood and willow, although this herbicide will harm most anything green. Notice must be posted before spraying due to possible fish contamination. Hand-held or tractor-mounted wick applicators can be very effective in the application of foliar herbicides to relatively low dogwood and willow stems.
Grey dogwood can be successfully controlled by cutting stems in summer and fall, and then carefully applying an herbicide to cut stems using a spot applicator. Basal bark application may also be effective.
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