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

Experiment Station. S Italic numbers in parentheses refer to "Literature Cited" at the end of this paper. 'T"he literature is not unanimous regarding designation of the qualities that determine the efficacy of insecticides and fungicides. Thus the amount of spray per unit of surface remaining after application, is called "initial spray deposit" (16), "deposition" (8), "initial adhesiveness" (9), and "retention" (fB); the distribution of the material over the surface is "coverage" (3) ; and the resistance to weathering is "adherence" (10) or "tenacity" (2). Horsfall, Heuberger, Sharvelle, and Hamilton (8) designate as "fungicidal value" that ability of the material to prevent spore germination; but the present writer prefers "toxicity" or "toxicological value." [491 ] 492 Hilgardia [VOL.14, No.9 EFFECT OF PETROLEUM OIL, COTTONSEED OIL, AND BENTONITE ON TENACITY OF BORDEAUX Each spray treatment was given in the autumn to four randomized plots, each containing four Paloro peach trees of fairly uniform size. The treatments were bordeaux mixture (10-10-100) to which had been added different amounts of petroleum-oil emulsion, tank-mix petroleum oil, cottonseed oil, or bentonite. Emulsion A was a flowable-type emulsion containing 80 per cent, by weight, of a petroleum oil of 102 seconds Saybolt viscosity and 70 per cent unsulfonated residue. Tank-mix oil was a. petroleum oil similar to that in emulsion A emulsified with blood albumin just before it was added to the spray tank. Emulsion B was a paste-type emulsion containing 82 per cent, by weight, of a petroleum oil of 96 seconds viscosity and 94 per cent unsulfonated residue. The cottonseed oil was a commercial grade. The bentonite was a natural product containing some magnesium oxide. As soon as the spray dried, 200-to 250-gram samples of twigs produced during the past summer were collected and weighed. The twigs were then cut into convenient lengths, placed in glass jars, and shaken for 10 minutes with 500 co of nitric acid water (20 cc nitric acid, of 1.42 sp. gr., per liter). The wash water was filtered and tested for copper by the sodium diethyl dithiocarbamate method" that Callan and Henderson (1) described. Other collections were made after several inches of rain had fallen (December or January) and a.gain just before the buds swelled in the spring (February). The amounts of copper on these samples were the basis for determining the weather resistance or tenacity of the bordeaux. Experiments of 1936-37.-Sprays were applied November 20,1936, well before the first major wave of twig infection by Coryneum which was initiated during rains falling between December 20 and 28. The season was marked by recurrent attacks of the disease during January, February, and March-particularly severe being a wave initiated in early March. According to the November 20 analyses (table 1), considerable variability existed in the initial amount of copper deposited by the various treatments. These data, together with those secured in other years, will be discussed later.

Leaf blight occurs in the Sacramento Valley and in the northern part of the San Joaquin Valley on most varieties of almonds. This disease has not been reported from any other part of the world. On highly susceptible varieties (Drake, Ne Plus Ultra, and Peerless) 15 to 20 per cent of the leaves may he destroyed during the growing season. An immediate reduction in productivity, however, results from the loss of leaf and flower buds, which are killed by the extension of the causal fungus tl Lendcrso nia rubi Sacc.) from the base of the leaf petiole into the supporting twig. Leaf blight is identified by the sudden wilting and dying of leaves throughout the summer. Although a few affected leaves fall, most do not. Fragments of the petioles remain on the tree and produce conidia the following winter and spring. The conidia of the fungus are shaped much like conidia of Coryneum beijerinckii Dud. (cause of the Coryneum hlight of almond) but are much smaller. Control may be obtained by spraying trees with either an eradicarive or a protective fungicide. The eradicat ive fungicide, sodium pentachlorophcnoxide, applied in spring just he fore the buds begin to open is effective against hath leaf blight and the brown-rot blossom blight disease caused by Sclerotinia laxa. N-phenylmercuriethylenediamine is also an effective eradicarive fungicide against the leaf blight fungus. Protective fungicides (capran, ziram, and dichlone) applied at the petalfall stage of bloom, as recommended for the control of Coryneum blight, also reduce infection by the leaf blight fungus.

in the Experiment Station. S The basic copper sulfate designated as A (Basi-Cop) contained 52 per cent metallic copper; that designated as Z (Zinc-Coposil) contained 19 per cent copper; the cuprous oxide (yellow eoprocide) contained 84-85 per cent copper. , The trade name of supplement A is Basi-Spred; of supplement B, Ortho-Adhesive.