ABSTRACT

This literature review provides a general overview of the dwarf mistletoes, Arceuthobium spp., with emphasis on those species which affect host plants which are members of the family Cupressaceae. A detailed review is given of the current status of Arceuthobium oxycedri in forests of Juniperus excelsa in the Province of Balochistan, Pakistan

Arceuthobium spp. are parasitic seed plants which infect trees and shrubs of the coniferous families Cupressaceae and Pinaceae. This is the only genus of Mistletoes which occurs in both the eastern and western hemispheres. Many species are damaging and cause reductions in increment and tree mortality. As of 1996, 42 species of Arceuthobium were recognized. Most species (34) are found in the New World, predominantly western North America with others occurring in the Caribbean basin, Central America, the Azores, Mediterranean Europe, North Africa, eastern Africa, the Near East, the Indian subcontinent and China.

The biology and life history of all Arceuthobium spp. are similar. Characteristics of the biology of this group of plants which make them amenable to pest management are; they are obligate parasites, are generally host specific, have a long life cycle and generally require 4-6 years to produce seeds, have a relatively slow rate of spreads and the presence of infection is easily recognized. General guidelines for prevention and management of dwarf mistletoe infections are presented.

Three species of Arceuthobium infect members of the conifer family Cupressaceae; A. azoricum, A. juniperi-procera and A. oxycedri. A. azoricum is endemic to the Azores where it infects Juniperus brevifolia, also an endemic. This dwarf mistletoe produces distinct gall-like swellings on the distal portions of branches of its host. A. juniperi-procera is known from Ethiopia and Kenya where it infects Juniperus procera, an economically important species, and is characterized by having an extended flowering period. A. oxycedri has the widest distribution of any species of Arceuthobium and occurs from Spain through Mediterranean Europe, North Africa, the Near East, the Indian subcontinent and China. It also has a wide host range and will infect virtually any species of Juniperus occurring within its natural range (natural or introduced). There also reports of its occurrence on Chamaecyparis thyoides, Cupressus arizonica and C. macrocarpa, all of which have been introduced into portions of the natural range of A. oxycedri. There are reports of this dwarf mistletoe causing serious damage to host plants in Azerbaijan, the Crimean Peninsula of the Ukraine, central Spain and India.

A. oxycedri, was "discovered" in the Sasnamana Valley, near the community of Ziarat, Province of Balochistan, Pakistan, in 1973 in conjunction with a forest disease survey. However, there is evidence that its occurrence was known by local people at least since the 1920s and the aerial shoots were collected and used as feed for livestock. Subsequent surveys established the presence of this parasite in the neighboring Chasnak Valley. The host tree is currently designated as Juniperus excelsa but it has also been reported in the literature as J. polycarpos and J. macropoda. Area of infection is a single, more or less contiguous area which, in 1993, encompassed ca 4 000 ha, equivalent to less than 5% of the total area of juniper forest in the Ziarat-Lorelei Forest districts. Initially, 50% tree mortality was attributed to the infection but later surveys established an infection rate of 36% and a mortality rate of about 13%.

The primary values of the juniper forest in the Zairat-Lorelei forest districts include cover for watersheds which are critical for local agriculture, summer range for livestock, a local source of fuel wood and summer recreation. In addition, the presence of very old trees (> 2 000 years) makes this forest of potential scientific interest.

Surveys conducted during 1993 indicated that the heaviest infection occurred on the north facing slopes of the Chasnak Valley (% trees infected = 53% DMR = 2.10) and that infection intensity in the Sasnamana Valley was significantly lighter (% trees infected = 31%, DMR = 0.54).

In 1978, a dwarf mistletoe control project was undertaken in the Ziarat area with the objective of eradicating this parasite over a period of 5 years. During this period, over 24 000 infected trees are either felled or pruned. The project was terminated in 1983 due to lack of funds. However, it was known that latent infections remained in the infected area.

Recommendations for management of dwarf mistletoe in the Ziarat Area of Balochistan, based on field observations made by the author in 1993, are presented.