Tree Profiles: Flowering Dogwood (Cornus florida), Part 2
This is the second half of a two part series on flowering dogwood. The following examines the cultivation of the tree, as well its damaging agents and pests, allergenic potential, and various uses.
Flowering dogwood (cornus florida), also referred to as dogwood or cornel, is one of the most popular ornamental trees in North America. It is considered an understory tree, developing beneath many other tree species, including oaks, hickories, yellow poplar, sweetgum, Virginia pine, loblolly pine, American beech, and red maple. Flowering dogwood often grows in conjunction with blueberry, sassafras, serviceberry, and brambles.
Flowering dogwood is a popular selection for cultivation in the United States. Many cultivars are highly regarded for their various attributes. Over one hundred cultivars are recognized by federal authorities; more than twenty cultivars are sold for commercial and personal use. Flowering dogwood cultivars are generally divided into groups based on certain characteristics, including flower size, flower color, leaf variegation, and growth habit. Flowering dogwood is generally cultivated from seed. Seed that has been cold stratified for 90 to 120 days has an almost perfect germination rate. Flowering dogwood is not known to hybridize with other species.
The four cultivars most commonly propagated as ornamentals are ‘Cornus florida f. pendula’, which is notable for its pendulous branches, ‘Cornus florida f. rubrum’, which features red or pink bracts, ‘Cornus florida f. pluribracteata’, which develops six or eight bracts of varying sizes, and ‘Cornus florida f. xanthocarpa’, which produces yellow fruit. In Central America, ‘Cornus florida var. urbaniana’ is widespread across the mountains of Nuevo León and Veracruz, Mexico. This cultivar features distinct gray twigs, and large fruit.
Damaging Agents and Pests
The most serious disease of flowering dogwood is dogwood anthracnose. Dogwood anthracnose is a fungal disease that has crippled dogwood populations across the eastern United States. The fungus requires wet conditions to thrive. As such, trees growing on moist, shady sites are most susceptible. When afflicted, trees will decline quickly, usually failing within two to three years.
Many insects have been identified as injurious to flowering dogwood. Dogwood borer (Synanthedon scitula) is a notable pest of many cultivars. Clearwing moth often invades dogwoods weakened by improper pruning cuts, or sunscald damage. Three types of borers are attracted to flowering dogwood. These include the flatheaded borers Chrysobothris azurea and Agilus cephalicus, and the dogwood twig borer Oberea tripunctata. Leaf miners cause brown blister-like mines to appear on the undersides of leaves. Twig girdlers (particularly Oncideres cingulata), scurfy scale (Chionapsis lintneri), and dogwood scale (C. corni) are also potential pests.
Dogwood club gall is a swelling that occurs on small twigs. It is caused by infestations of midge larvae (Resseliella clavula). Various leaf feeders consume the foliage of flowering dogwood. Some of the most prevalent include the redhumped caterpillar (Schizura concinna), the tussock moth Dasychira basiflava, and scarab beetles (Phyllophaga spp.). The Japanese weevil (Psuedocneorhinus bifasciatus) and Asiatic oak weevil (Cryptepistomus castaneus) frequently attack dogwood in areas where the insects have been introduced.
Basal stem canker is caused by the fungus Phytophthora cactorum, and is capable of girdling the tree. It is considered amongst the most lethal diseases of flowering dogwood. The fungus Myxosporium nitidum causes twig blight, which is often responsible for the dieback of small twigs. Target cankers sometimes occur on the trunk and limbs of flowering dogwood. Armillaria mellea, also known as honey fungus, is a soil-borne fungus that causes root rot in susceptible trees. Flowering dogwood is sometimes infected by powdery mildew, a disease caused by the fungi Microsphaera and Phyllactinia. Meliodogyne incognita, a nematode, can cause severe root galling, which often results in foliar dieback and premature leaf fall.
The leaves and flowers of flowering dogwood are susceptible to spotting and wilting from the fungi Botrytis cinerea, Elsinoe corni, and Septoria cornicola. The fungus Ascochyta cornicola sometimes casuses the leaves to shrivel and blacken. Verticillium wilt (Verticillium albo-atrum) is a significant fungal disease that decimates healthy foliage. Cherry leafroll, tobacco ringspot, and tomato ringspot have also been found on dogwood leaves.
Due to its thin bark, flowering dogwood is easily wounded by fire. The thin bark also causes the tree to more easily sustain mechanical, and pruning injuries. Flooding is detrimental to flowering dogwood. Prolonged flooding often results in root rot. In winter, flowering dogwood may incur frost or wind damage.
Flowering dogwood is classified as a mild allergen, making it ideal for many planting sites.
Flowering dogwood is a valuable source of food for wildlife. The fruits are consumed by more than 36 species of birds, including ruffed grouse, bob-white quail, and wild turkey. Chipmunks, foxes, skunks, rabbits, deer, beaver, black bear, and squirrels are among the many mammals that feed on dogwood fruits. The foliage and twigs are heavily browsed by deer and rabbits.
Dogwood was commonly harvested for use in the manufacture of shuttles for textile weaving. However, plastic shuttles have since replaced this use. Small amounts of harvested wood are sometimes used in the production of spools, small pulleys, mallet heads, jeweler blocks, tool handles, charcoal, knitting needles, turnpins, walking canes, arrows, mountain dulcimers, the heads of certain golf clubs, and fruit presses. They may also be used to create scarlet inks and dyes. Early laminated tennis rackets were crafted from thin strips of dogwood.
Native Americans crafted an herbal infusion from dogwood flowers to treat fevers and colic. The roots, stems, and twig bark were used as a substitute for quinine. Flowering dogwood is the state tree of Missouri and Virginia. The blossom of the dogwood tree has been designated the state flower of North Carolina.