Olive leaf spot and its control with fungicides

Abstract

REPEATED OUTBREAKS of the leaf spot disease of olives (Olea europaea I..J.) caused by the fungus Oycloconium oleaginum Cast., have occurred in California for the past seven or eight years. This disease is well known in Mediterranean countries and has received the attention of plant pathologists there since the middle of the last century. Although known in California for over fifty years, olive leaf spot received little attention until the recent outbreaks. In 1941 I. J. Condit' and the late W. T. Horne, of the University of California Citrus Experiment Station at Riverside, began observations on the disease at Fall Brook, San Diego County, and in 1942 conducted certain spray tests. Condit and Horne's data (not published) indicate that a material reduction in infection followed applications of bordeaux sprays. In January, 1944, we began fungicidal tests and observations on disease development at Fair Oaks, Sacramento County. The trials were conducted at this location until 1946, when the work was transferred to an orchard near Orland, Glenn County. The results of the observations and tests are presented herein. THE DISEASE Common Names. The disease has been called "bird's eye spot," "leaf spot," "peacock spot," and "Oycloconium leaf spot," the last name probably appearing most frequently in the literature. Symptoms. Although symptoms most often occur on the leaf blade, they are sometimes found on leaf petiole, fruit, and fruit stem (Petri, 1913; Berries, 1923). Condit and Horne observed lesions on fruit and fruit stems in San 1

Effect of temperature, relative humidity, leaf wetness and leaf age on Spilocaea oleagina conidium germination on olive leaves

“…The temperature range of 5 to 25°C observed for conidium germination on detached olive leaves is similar to that reported previously for S. oleagina conidium germination by Saad and Masri (1978). However, other researchers have reported conidium germination on agar to occur at a minimum of 5°C, with an optimum of 20°C, and a maximum of 30°C (Wilson and Miller 1949;Dzaganiya 1967;Kashy et al 1991), although Mijuskovic (1969) reported germination occurring on agar at 7 to 28°C with an optimum of 14 to 19°C. The wide range of temperatures at which S. oleagina conidia germinate suggests that infection may occur throughout the year in olivegrowing regions with mild temperatures leading to high OLS disease levels since young susceptible olive leaves are always available in groves.…”

“…However, despite the yield losses caused by OLS in some areas very little is known about the biology of the pathogen and some results appear to be contradictory. For example, the temperatures for conidium germination on agar were reported by Wilson and Miller (1949), Dzaganiya (1967), and Kashy et al (1991) to be a minimum of 5°C, an optimum of 20°C, and a maximum of 30°C. Chen et al (1981) also showed that conidium germination on agar occurred in the temperature range 6 to 28°C, with an optimum at 16 to 20°C.…”

“…In California, Wilson and Miller (1949) reported severe outbreaks of OLS in the period 1941 to 1949, with yield losses of up to 20% in some areas. In the Mediterranean olive-growing regions, which are characterized by long dry summers, OLS is controlled by application of copper-containing fungicides prior to winter rains (Teviotdale et al 1989).…”

Use of Cu Fungicides in Vineyards and Olive Groves

“…Today, it is present throughout the world, in all olive-growing regions. The disease is common worldwide and causes serious problems in cooler olive-growing regions, with yield losses estimated to be as high as 20% (Wilson & Miller, 1949). Experts regard it as one of the most widespread and dangerous olive fungal diseases (Obonar et al, 2008).…”

“…In Mediterranean regions, such as Italy and Spain, three fungicide applications (end of winter, end of spring and late autumn) are recommended (Graniti, 1993). In Californian olive groves a single spray of copper-sulphate (Bordeaux mixture) gave satisfactory control of olive leaf spot when applied prior to rains in autumn or early winter (Wilson & Miller, 1949). Some authors also reported that one annual application of copper-based fungicides in late autumn, before the rainy period, effectively controlled olive leaf spot under low disease attack in Californian olive-growing region (Teviotdale et al, 1989).…”