Sudden Oak Death

From Freepedia

Sudden Oak Death

Scientific classification

Kingdom:	Protista
Phylum:	Heterokontophyta
Class:	Oomycetes
Order:	Pythiales
Family:	Pythiaceae
Genus:	Phytophthora
Species:	P. ramorum

Binomial name

Phytophthora ramorum
Werres et al. 2001

Sudden Oak Death (Phytophthora ramorum) is a water mould infection which afflicts some oak species and some other trees and shrubs, causing them to die rapidly. It also causes a non-fatal leaf disease in many other plants such as rhododendrons and California Bay Laurel. There is no known cure but new studies show that periodic wildfires help protect against the mould.

It was first discovered in California in 1995 when large numbers of Tanoaks (Lithocarpus densiflorus) died mysteriously, and was described as a new species of Phytophthora in 2000. It has subsequently been found in many other areas including Britain, Germany, and some other US states, either accidentally introduced on nursery stock, or already present undetected. The origin of the disease remains unknown, although it was reported infecting European nursery rhodendrons and viburnum in 1993.

In tan oaks, the disease may be recognized by wilting newshoots, older leaves becoming pale green, and after a period of two to three weeks, foliage turns brown while clinging to the branches. Dark brown sap may stain the lower trunk's bark. Bark may split and exude gum, with visible discoloration. After the tree dies, suckers will sprout next year, but thier tips soon bend and die. Ambrosia beetles (Monarthrum scutellare) will most likely infest a dying tree during midsummer, producing piles of fine white dust near tiny holes. Later, bark beetles (Pseudopityophthorus pubipennis) produce fine red boring dust. Small black domes, the fruiting bodies of the Hypoxylon fungus may also be present on the bark. Leaf death may occur more than a year after the initial infectgion and months after the tree has been girdled by beetles.

In coast live oaks and black oaks, the first symptom is a burgundy-red to tar-black thick sap bleeding from the bark surface.

Promoting tree health may help prevent disease and insect infestations. Make certain roots and soil remain undisturbed, prune dead and dying branches out, and landscape below oaks with mulch or drought-tolerant plants. When a tree dies, experts recommend cutting it down and grinding down the stump. Firewood should be covered with 6 mil plastic, sealed at the edges with dirt or rocks, for six months to prevent beetle emergence.

In addition to oaks, any other forest species may be host for the disease, including rhodedndron, madrone(Arbutus menziesii), evergreen huckleberry (Vaccinium ovatum) California bay laurel (Umbellularia californica), buckeye (Aesculus californica), big-leaf maple (Acer macrophyllum), toyon (Heteromeles arbutifolia) and manzanita (Arctostaphylos spp.) Coastal redwoods (Sequoia sempervirens), Douglas fir (Pseudotsuga menziessi), coffeeberry (Rhamnus californica),and honeysuckle (Lonicera hispidula) and Shreve's oak (Quercus parvula v. shrevei) are also afflicted. Disease progression on these species is not well documented but hikers have observed dead Douglas firs with massive quantities of red frass surrounding their base. Redwoods exhibit needle discoloration andcankers on small branches, with purple lesions on sprouts that may lead to sprout mortality.

The disease is known to exist in California's coastal ranges bewteen Big Sur and southern Mendocino County and is confirmed in Alameda, Marin,Mendocino,Monterey, Napa, San Mateo, Santa Clara,Santa Cruz, Solano and Sonoma counties. It is reported in Orgeon as well as of 2002.