Grey Osier Dogwood (Cornus racemosa)
DESCRIPTIONS
Dogwood: Of the five species of dogwood shrubs found in Wisconsin, only gray (Cornus racemosa) and red osier (C. Sericea) seem to be troublesome. Both species are multi-stemmed shrubs commonly reaching a height of 8 feet. The simple leaves of this genus occur in opposite arrangement; their margins are not distorted by lobes. The flowers are borne in a cyme of four small petals and four minute sepals. Each flower forms a fruit, called a drupe, that bears a single seed. Red osier dogwood has bright red twigs, while gray dogwood twigs are maroon-brown to gray.
DISTRIBUTION AND HABITAT
Dogwood: Grey and red osier dogwoods enjoy a wide distribution that includes the northern, temperate climates of the United States. Red osier prefers the moist soils of damp woodlands, riparian zones, flood plains, and in some cases, mesic woods and moist flats. Grey dogwood is often found in slightly drier areas, including mesic prairies.
LIFE HISTORY AND EFFECTS OF INVASION
Dogwood: These shrubs reproduce both sexually and vegetatively. Flowers bloom between March and July, depending on region. Fruits are generally borne in September or October, and are dispersed by gravity, birds, and other animals. Germination of the seeds occurs the following spring. The best natural seed beds are moist, well-drained, rich loams. Dogwoods can reproduce vegetatively through suckers, sprouts, and root shoots. They seem to grow best in areas of intermediate light intensity, although they can survive both in direct sunlight and as an understory plant.
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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