Contact: Bud Reaves, Anne Arundel County | ipreav00@aacounty.org
ANNAPOLIS, MD (April 3, 2018) – Every year in late March and early April, cherry trees burst forth into bloom in Maryland. Some of the first to bloom in the spring, cherries are among the showiest flowers in the forest. However, most of the cherry trees that get the attention are non-native species brought here for their showy flowers or their tasty fruit, and some may become invasive. To observe the coming of spring, the genus Prunus, including cherries and their relatives, has been chosen as the April Invader of the Month.
Prunus is part of the Rose family, Rosacea, which consists of approximately 430 species. The fruit from Prunus species are known as stone fruits for their hard pits. All parts of Prunus species are toxic except for the fruit. Prunus species include deciduous and evergreen members with a few having spiny stems. Leaves are always simple and alternate, usually lanceolate, sometimes round, unlobed, and often with necataries or glands on the leaf stalk. Flowers are white or pink with five petals and sepals and numerous stamens, and are borne singly or in umbles of two or more on racemes. Species included in the genus are cherries, almonds, peach, plums, nectarines and apricots. In addition to the 430 or so species within the genus there are numerous cultivars of these economically important trees.
In North America there are approximately 30 native species in the genus Prunus, including numerous plums and several cherries. The plum species are most valuable as food for wildlife, such as birds and small mammals, which depend on the nutritious fruits during the summer and fall. Native plums are edible by humans but are not cultivated regularly. The native cherries are also valuable to wildlife but are generally not eaten by people due to their small size. Black cherry, Prunus serotina, is the most common native cherry and is a highly valuable timber tree used for furniture and cabinetry. Black cherry is also very important for wildlife. The fruit is consumed by numerous birds and mammals and is a source of nectar and pollen for many pollinators. Ironically, its use as an ornamental has led to it becoming an invasive species in Europe.
Exotic members of the Prunus genus are also found throughout North America, introduced for ornamental purposes or planted for their fruit. Ornamental cherries are the most common, notably the ‘Yoshino’ cherry, Prunus yedoensis, a hybrid of two other ornamentals, which are famously the focus of the Cherry Blossom Festival held in Washington, D.C. every spring. Other notable ornamentals include the ‘Kwanzan’ cherry, a cultivar of Japanese Cherry, Prunus serrulata. The ornamental cherries as a whole are not known to be invasive. As cultivars they bear either no fruit or small amounts of fruit. Like most cultivars, Yoshino and Kwanzan cherry are cultivated by grafting.
Bark, fruit, and leaves of invasive sweet cherry, Prunus avium. Photo: Robert Vidéki, Doronicum Kft., Bugwood.org
Fruit-bearing Prunus species, including cherries and plums, can be invasive. In Maryland, sweet cherry, Prunus avium is the most common invader. It has been reported in thirteen Maryland counties including Baltimore City, according to the Maryland Biodiversity Project. Sweet cherry, of which there are abundant varieties, bears fruit on spur shoots that produce white flowers in April, with fruits ripening in late June or July. The bark on sweet cherry is distinctive, described as smooth purplish-brown with prominent horizontal grey-brown lenticels. Leaves are somewhat shiny above and spear shaped. Sweet cherry is spread by birds and is found on the edges of forests and hedge rows, and in forest interiors. Occasionally, it will form stands, displacing native species. Sour cherry, Prunus cerasus, has a similar habit and can be found in the same areas as sweet cherry. It is a smaller tree than sweet cherry with similar bark, with the leaves having more rounded serrations on the edge. It has been reported in seven counties, mostly in the central part of the state. A few other cherries including Mahaleb cherry (Prunus mahaleb) and Nanking cherry (Prunus tomentosa Thunberg) have also been reported in Maryland
The threat from non-native species of the Prunus genus is broad. Members of this genus will spread to forests and hedgerows through dispersal of their fruit by birds and mammals. This can displace native species of the genus that have similar habitat requirements. Exotic Prunus species also serve as hosts for various diseases such as brown rot and leaf spot that affect orchards and ornamental plantings, and insects such as the peach tree borer.
Managing these exotic fruit bearing trees has value to native forests, farms, orchards, and nurseries alike. Trees in in this genus are generally shade intolerant and can be excluded by keeping a closed canopy in the forest. Individuals can be girdled with the application of an appropriate herbicide to prevent resprouting using label recommendations for rates. If planting a tree for ornamental purposes, use a cultivar that doesn’t bear fruit. Enjoy the flowers and fruit, but don’t forget the forest.