Temporal and Spatial Epidemiology of Phytophthora Root Rot in Fraser Fir Plantations.

In 1999, 19 plots of Fraser fir (Abies fraseri) with a disease focus were established in commercial plantings grown for Christmas tree production in the mountains of five western North Caro-lina counties. Progress of Phytophthora root rot caused by Phytophthora cinnamomi as estimated by mortality was followed in each plot over 3 to 4 years in an attempt to understand dispersal of inoculum. Slope, aspect, and field production age at the time plots were established were recorded. Rainfall estimated from National Weather Service stations each growing season also was recorded. The relationship of site parameters and rainfall to dispersal and disease was investigated. Disease incidence and mortality were assessed in June and September each year for 3 or 4 years depending on plot. Phytophthora root rot as estimated by mortality counts over time in a logistic regression model progressed in only five of 19 plots over 3 years. None of the site parameters correlated with mortality data, although slightly more disease was found in plots with a north aspect. Rainfall was below normal in the 3 years of the study and did not correlate with mortality in any year. Lack of disease progress in the majority of plots was attributed to drought conditions in the region. In the five plots where mortality increased over time, spatial analysis suggested an aggregated pattern of diseased plants. Aggregation was apparent but not very strong among nearest neighbors, but was considerably stronger among groups of trees within a local area. This aggregation within groups was stronger when larger group sizes were examined by beta-binomial analysis. A spatial analysis by distance indices method (SADIE) indicated the presence of secondary clusters occurring several meters away from the main focus. A stochastic model also was employed that indicated a combination of spatial processes were likely involved, specifically a tendency toward spread within a local area, but not necessarily to the nearest neighboring trees, combined with an influence of background inoculum that could not be accounted for within local areas and may have come from external sources. Thus, all sources of inoculum including infected planting stock, inoculum in soil, infected trees, and contaminated equipment were equally important in epidemics of Phytophthora root rot in Fraser fir and dispersal of P. cinnamomi.

First Report of the Telial Stage of Gymnosporangium exiguum on Ashe Juniper Adjacent to Hawthorn with Rust in Southwest Texas.

The telial stage of Gymnosporangium exiguum (2) on Ashe juniper (Juniperus ashei) was observed in Bandera County, TX, in April and May 1999 after rain events. Symptomatic plants with multiple lesions were found at low frequencies in dense J. ashei populations. Orange telia formed on scales and bark and on 2- to 3-mm-diameter twigs and became nearly inconspicuous when dry. No hypertrophy was observed. Previously reported telial hosts include J. californica and J. excelsa cv. Stricta in California; J. mexicana and J. scopulorum in Oklahoma; J. virginiana in Texas; and J. deppeana var. pachyphloea in Oklahoma and Texas (1). An aecial stage identified as G. exiguum has been observed for many years on native hawthorns (Crataegus crus-galli, C. greggiana, C. mollis, C. stevensiana, C. tracyi, C. turnerorum, C. viridis var. desertorum, and several natural hybrids) in Bandera, Bexar, Edwards, Gillespie, Kendall, Kimble, Real, and Uvalde counties, Texas. Prominent roestelioid aecia were observed on hawthorn leaves, petioles, fruits, peduncles, thorns, and, less often, on twigs. In two experimental plantings of hawthorns in Bandera County, rust severity was rated as low to moderate in six populations of C. greggiana and hybrids; moderate in two populations each of C. stevensiana and C. tracyi; moderate to severe in three populations of C. crus-galli and hybrids; and severe in one population each of C. mollis and C. viridis var. desertorum. G. exiguum was previously reported on a Crataegus sp. in Texas and on Heteromeles arbutifolia in California (1). Flowers, fruits, plant forms, and drought tolerances are characteristics of some endemic hawthorns that provide landscape and wildlife advantages. G. exiguum causing rust disease may limit the ornamental potential of highly susceptible hawthorn species in southwest Texas. Inconspicuous infections on susceptible ornamental Juniperus spp. also could have phytosanitary implications. Voucher specimens (aecia and telia) are on deposit in the Mycological Herbarium, Department of Plant Pathology, North Carolina State University, Raleigh. References: (1) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN. (2) F. D. Kern. 1973. A Revised Taxonomic Account of Gymnosporangium. The Pennsylvania State University Press, University Park.

First Report of Thyronectria austroamericana Canker on Thornless Honey Locust in North Carolina.

Specimens from a thornless honey locust (Gleditsia triacanthos var. inermis 'Shade Master') with cankers were submitted in May 1999 to the North Carolina State University Plant Disease and Insect Clinic by staff from the North Carolina Zoological Park (Asheboro). Abundant stromata of Gyrostroma austroamericana, the anamorph of Thyronectria austroamericana, were associated with the cankers. A visit to the Zoological Park during August 1999 revealed seven additional honey locust trees with multiple branch and stem cankers and dieback. All infected trees had perithecia of T. austroamericana and/or its anamorph. The fungus is distinguished by the large clusters of yellow-brown perithecia with dark brown tips produced on stromata emerging from lenticels, elliptical muriform ascospores, and sparse ascoconidia (1,2). Ascoconidia form as the result of ascospores budding within the ascus. Other trees of the cultivar are an integral part of the landscaping theme of the African Pavilion of the park, and park staff were concerned about disease spread. Infected trees were 8 years old, and several had evidence of sunscald cankers, a common infection court of T. austroamericana (2). Thornless cultivars of honey locust are popular landscape plants in the central and eastern United States and may be seriously affected by T. austroamericana (2). Apparently 'Shade Master' is very susceptible to the fungus and should not be used as a landscape tree, especially where the disease has been reported. This is the first report of T. austroamericana in North Carolina on any host. Voucher specimens have been deposited in the National Fungus Collection, Beltsville, MD (BPI 74693), and in the Mycological Herbarium, Department of Plant Pathology, North Carolina State University, Raleigh. References: (1) E. V. Seeler, Jr. J. Arnold Arbor. Harv. Univ. 21:429, 1940. (2) W. A. Sinclair et al. 1993. Diseases of Trees and Shrubs. Cornell University Press, Ithaca, NY.