The Chokecherry Tree
By Melissa Ruth Bjerke

 

Abstract

The chokecherry tree is a well known fruit tree with information readily available concerning growth, features, and diseases. However, information involving methods of propagation and future economic potential of this plant has not been written about widely. Over the course of the next few years, these aspects of chokecherry production is likely to become more thoroughly researched.

Introduction

The chokecherry tree, a member of the Rose family, may not be as famous as some of the other rose family members such as the plum, peach, apple and almond tree, but many people are discovering that it has many attractive qualities that a n increasing number are incorporating into the landscape of their yard. Many also enjoy the autumn harvest of berries or even conventional purposes such as windbreaks. Unfortunately, just as the other stone fruit species are susceptible to disease, the c hokecherry is no exception. Propagation and breeding research which may help decrease the threat of these diseases is fairly new concerning the chokecherry tree, but many advances have and will be made for years to come.

Classification

The chokecherry is a humble tree, known to nearly everyone as it grows wild throughout the United States and Canada, but many are realizing its aesthetic qualities and planting it in the domestic environment of their homes. The family < I>Rosaceae claims nearly 200 species under the Genus Prunus, consisting of trees and shrubs. Forty different species of the chokecherry tree can be found throughout the United States and Canada, particularly more abundant in the northern regio ns. They can all be classified into three major groups; Common, Western and Black chokecherry trees. (Aipperspach, 1980).

Growth

The appearance of chokecherry trees in varied climates suggest that it is very adaptable, and particularly winter hardy. Prunus virigianiana grows as a medium to tall shrub generally, but if grown in unfavorable conditions, it tends to be more shrub-like and in prime conditions, it grows like a tree up to twelve feet. Prime conditions include a sunny location and moist rich soil. It is not especially choosy about the soil in which it grows, but it does not do as well in poor , shallow or deep, sandy soil.

Production and Use

One of the most attractive features of the chokecherry tree is the mass of dense flowers clusters at the end of the branches. These flowers normally bloom during the latter part of May. In the fall, from August to September, the chokecherr ies have ripened and are ready to be harvested if one wishes to do so. The berries are typically a very dark red with a rounded shape. It is hard to believe that people have found ways to make even the bitter taste of the chokecherry edible, but many en joy chokecherry jellies, wines, and syrups. The chokecherry was once a staple for the Native Americans who used it to make pemmican and also stored it frozen or partly dried to be eaten throughout the winter.

However, chokecherries can also be poisonous. The seeds, leaves, and bark of many stone fruits contain glycoside, which produces cyanide. In addition, the chokecherry produces prunasin, which is similar to cyanide. But fortunately, they are not any more dangerous than eating plums or apples because the flesh is not poisonous in these fruits. Livestock have reportedly died due to consuming the fruit in large quantities, but these are normally under poor feeding conditions and the chokecherry leaves were a last resort for food.

Disease and Pest Management

As the chokecherry tree is being more utilized, people must also keep in mind the diseases that it is prone to become infected with. Most of these diseases are common to all stone fruit trees and some infect other trees as well.

One of the most common diseases to be aware of is the Black Knot fungus, Dibotryon morbosum. It is recognized by long, black swellings at the tips of branches that eventually kill them. Severe infections may involve the fungus girdling the mai n branches of the tree or the stem, but this seldom occurs. To control this fungus, knots must be removed in the spring by pruning the infected branch four to five inches below the knot. Knots should be destroyed by burying or burning them. Removing th ese knots early prohibits the release and dispersal of its spores to infect other plants or reinfect the same tree. Pruning may need to be done annually for several years due to the long time before the fungus is visible. Use of fungicides, in addition to pruning, will ensure the best removal of the fungus. Orthorix or Bordeaux mixture should be applied before bud break in the spring and captan and benomyl should be applied weekly throughout the month of June.

Another disease infecting stone fruits is a fungus that produces "plum pockets". These are characterized by the fruits becoming as large as eight to ten times their regular size, hollow and having a distorted color and shape resulting in sev ere fruit loss. This fungus may also cause the leaves and shoots to curl. Removal of the infected fruits after they have fallen prove to be of little value concerning control. Control relies mainly on the use of fungicides just before bud break, which is when the infection occurs. Lime sulfur or Bordeaux mix can be applied after the threat of freezing, but before bud break. Otherwise if foliage is evident, it will be burned by the chemical.

What may appear to be plum pockets on chokecherry trees, could actually be the effects of an insect, Contarinia virginianiae. This small fly is known as the chokecherry midge which lays its eggs on the fruit so that the larvae tunnel inside and feed on the meat of the fruit hollowing it out. Little is known on how to control this insect, except that fungicide sprays are of no benefit.

Brown rot, Monilinia fructicola, is also a trademark of all stone fruits. This disease is fairly inconspicuous to the homeowner until the ripening fruit develop the brown rot, rapidly wither, and fall to the ground. In favorable weather condit ions, such as warm and humid, fruits can rot in a matter of a few hours. Control for this fungus should begin in late summer or early fall by removing all infected fruit, all remaining fruit and all cankered twigs and burning or burying them. Fungicide sprays may be helpful. Benomyl or captan can be applied as soon as blossoms show color and then periodically according to recommendations.

Perennial cankers, caused by fungi Valsa cincta and V. leucostoma, may infect a tree for years until they eventually girdle the branches or stem resulting in death. Removing all sites of entrance for the spores of this disease is the bes t method of control. This can be achieved by removing cankered wood and destroying it and covering and protecting all pruning wounds with a fungicidal dressing. Captan fungicide spray can be applied to the entire tree after pruning, but prior to the nex t rainfall.

Bacterial infections are also problems for chokecherry trees. Bacterial spot, Xanthomonas pruni, and "shothole", Pseudomonas syringae, are recognized by leaves with a lot of little holes in them. Prior to this state, the leave s appear to have water logged spots on them, which turn black and fall out, leaving the holes. Infection of the fruits produce brown spots on them. These diseases are difficult to control but conscientious planting methods could reduce infections. Avoi d use of too much nitrogen in fertilizer and do not plant young, vulnerable trees next to old ones.

Powdery mildew is another fungus, Podosphaera oxyacanthae. It infects the leaves covering them with a powdery mildew causing them to curl upward. This disease is easily controlled with benomyl fungicide, but is usually not necessary in North D akota.

The chokecherry tree is a wild host for a stone fruit disease known as the X-disease. Infected trees reveal slow growth in the spring and six to eight weeks later, the berries become a bright orange or red and diseased leaves fall off. Fruit producti on is hindered throughout the entire life span of the tree until death which is about three to four years after infection. There is no cure for a tree that has been infected with this disease. They only control strategy is to plant disease-free stock and isolate those that are already infected.

Virus diseases attack stone fruits, such as the Prunus ringspot virus. Effects of this virus are yellow rings, lines, bands, spots and other abnormalities of the leaf. A virus common in the chokecherries inhabiting North Dakota is "common cherry yellows". Infected plants may live for several years, but exhibit poor branching, premature loss of fruit and eventually long, willowy, unbranched shoots, and little to no production of fruit. This disease also has no cure and removal or isolation of diseased stock warrants the only control.

Winter Injury

Other damage on chokecherry trees can be inflicted during the winter. Hard frosts in the spring can kill delicate budding shoots or rapid drops in temperature below freezing before the tree is completely hardened off or is just coming out o f dormancy in the spring can cause the trunk to split. Other winter injury includes sunscald. Sunscald occurs mostly in late winter when the sun warms the inner bark making it physiologically active, and then suddenly drops down to below freezing. This rapid change in temperature kills the inner bark which is a vital part of the plant because it contains the vascular cambium. The vascular cambium consists of the phloem and xylem which carries water and vital nutrients to the outer areas of the plant a nd its roots. The dead tissue may appear to be sunken in and discolored and is vulnerable to parasites and infection. To prevent winter sunscald, shade the southwest side of the trunk and main branches. They can also be wrapped in reflective paper or p ainted white with an interior water base latex paint to reflect the sunís rays and avoid the trunk and branches from warming. (All information about stone fruit diseases, control and winter damage was collected from Disease Control in Cherries, Plums, and Other Stone Fruits; North Dakota State University, NDSU Extension Service.)

Propagation

Propagation of the chokecherry consists of mostly seedlings. Seedlings are the main propagation material used because a majority of chokecherry trees cross-pollinate. Since chokecherries cross-pollinate so readily, nursery or orchard manag ement is almost impossible. (DNA Gardens Ltd.,1999) Cross-pollinating introduces new varieties and higher fruit yields. When planting chokecherry trees, it is recommended to plant more than one variety.

Cuttings of chokecherry trees may be used if a tree has been bred to possess specific qualities such as a sweeter fruit, dark purple foliage, or possibly even resistance to a disease. These particular features might be lost or weakened if cross-pollin ated so cuttings allow new plants to grow consisting of the exact same genetic make-up as the original plant. However, if many chokecherries were grown together, for example, in an orchard, it would not be desirable to grow only one type of cultivar. Rea soning behind this theory is that if one plant is infected with a disease, every other tree would also be susceptible to that disease which could infect the entire orchard. Another reason is that cross-pollination produces stronger plants, more resistant diseases and stresses such as climate and drought.

Current Research

Research and breeding of chokecherries has not been long underway. A program, initiated in 1993, was developed to breed superior fruiting cultivars. Anticipated release of twenty top clones was the spring of 1999. Breeding populations hav e been established at Indian Head, Star City, and Carman, Manitoba. Further research on stratification methods and sowing dates for propagation are still being researched. (Schroeder and Neill,1999)

References

    1. Aipperspach, L. B. 1980. Ecology of Prunus virginiania in North Dakota; M.S. Thesis, North Dakota State University.

    2. Anonymous. 1999. The rose family. http://www.ednet.ns.ca/educ/museum/poison/roses

    3. DNA Gardens Ltd. 1999. Tissue culture or seedling - what's the difference?.http://www.dnagardens.com/whatsthe.htm

    4. Lamey, H. A. and R.W. Stack. 1999. Disease control in cherries, plums, and other stone fruits. North Dakota State University, NDSU Extension Service. http://www.ext.nodak.edu/extpubs/plantsci/hortcrop/pp689w.htm

    5. Prairie Plant Systems Inc. 1999. Chokecherries http://www.prairieplant.com/fruit/choke.html

    6. Schroeder, W. and R. Neill. 1999. Horticulture research across the prairies - chokecherry research. http://www.ag.usask.ca/department/plsc/hratp/fruitcrops/choke.html

    7. Ward, T. The common chokecherry. 1999. http://www-ag.usask.ca/cofa/departments/hort/hortinfo/fruit/choke.html