Natural products alone or with copper vs. grape downy mildew: efficacy, costs, Cu impact.

In organic farming copper is one of the few fungicides that can be used and the only effective against downy mildew. Due to the problems of environmental impact associated with the use of this heavy metal, the European Union decided to restrict its use (Annex II Regulation EC n. 889/2008). In order to assess the possibility of replacing the copper or reduce the quantities used, we tested natural products and low rate copper formulations in field trials. The anti-downy mildew activity of these formulations has been studied in an organic vineyard. During the two years of activity we also estimated the economic cost of use of the products to assess their possible use in agricultural practice.

First Report of Twig Canker of Hazelnut Caused by Fusarium lateritium in Italy.

Cultivation of hazelnut (Corylus avellana L.) has considerable economic potential in Italy, in particular, in the northern Lazio Region. Since early summer of 2000, cankered twigs have been observed on hazelnut trees that were severely affected by gray necrosis, which is a disease complex causing fruit drop (1). In subsequent years, sunken areas were observed on 1-year-old shoots from late April through May. The resulting cankers had reddish brown margins and the death of the cambium in the infected area and produced an L-shaped malformation of twigs. Girdling of the twig by the canker resulted in death of the foliage. Yellow-to-orange sporodochia were evident on cankers by early June. Isolations were made from the margins of young cankers from 20 twigs collected from 10 trees. Tissue pieces were plated onto potato dextrose agar (PDA) after surface disinfection with 1% sodium hypochlorite. Slow-growing, cream-to-reddish brown colonies with sparse aerial mycelium emerged from 80% of diseased tissue pieces within 10 days of incubation at 20 to 22°C. Conidial production was induced by keeping pure cultures at 22 to 25°C under natural light but out of direct sunlight. Within 1 month, sporodochia bearing ellipsoidal, spindle-shaped, commonly 1 to 3 septate macroconidia developed. Intercalary chlamydospores were often present in chains. Single conidia were subcultured on carnation leaf agar (CLA). On the basis of morphological and cultural characteristics, the fungus was identified as Fusarium lateritium Nees. (2). Pathogenicity tests were conducted outdoors on the current year's shoots of hazelnut trees with four isolates derived from single conidia of F. lateritium. Inocula used were either mycelial plugs cut from the margin of actively growing cultures or small (10 × 10 mm) pieces of sterile cheesecloth soaked in 1 × 106 conidia per ml suspension. The mycelial plugs were placed under the bark, while the soaked cheesecloth pieces were wrapped around an area that had been wounded by gently scraping off a length of the bark (approximately 10 mm) with a sterile needle. All the inoculations were wrapped with Parafilm to prevent desiccation. Six inoculations per isolate were performed. In a similar manner, controls were inoculated with agar plugs or water only. After 3 months, the length and width of each canker were measured. For both inoculation methods, cankers were similar to those observed in nature and averaged 20.6 × 5 mm, while the controls did not show any symptoms. F. lateritium was consistently reisolated from the canker margins of the inoculated shoots. To our knowledge, this is the first report of F. lateritium causing twig cankers on hazelnut. The fungus has been reported to cause cankers on several tree species, including Malus domestica (apple), Morus spp. (mulberry), Sophora japonica (Japanese pagoda tree), Robinia pseudoacacia (black locust), Citrus spp., and Pyrus pyrifolia (Asian pear). References: (1) A. Belisario et al. Inf. Agrario 59(6):71, 2003. (2) P. E. Nelson et al. Fusarium Species: An Illustrated Manual for Identification. Pennsylvania State University, University Park, 1983.

First Report of Alternaria Species Groups Involved in Disease Complexes of Hazelnut and Walnut Fruit.

During the last 5 years, two new diseases, brown apical necrosis (BAN) and gray necrosis (GN), were observed on English walnut (Juglans regia) and hazelnut (Corylus avellana), respectively (2,3). Both diseases caused severe fruit drop resulting in yield loss often exceeding 30%. Previous work demonstrated that BAN and GN are disease complexes caused by several fungi (Alternaria spp., Fusarium spp., and a Phomopsis sp.) (2,3). In both diseases, preliminary identification of Alternaria spp. revealed they were a complex of small-spored catenulate taxa related to A. alternata. To further characterize these taxa, additional pathogenicity tests and morphological examinations were conducted with isolates obtained from each host. Single-spored isolates were prescreened for pathogenicity by inoculating detached, surface-disinfested hazelnut leaves or walnut leaflets (1). Only isolates that produced foliar lesions after 5 days were used in subsequent fruit inoculations. From this screening, 35 isolates were selected (19 from walnut and 16 from hazelnut). For each isolate, attached fruit of respective hosts were inoculated at bloom by placing 10 µl of a conidial suspension (1 × 106 conidia per ml of H2O + 0.26% agar) onto the stigmas (150 fruit per isolate). Controls (150 fruit) were treated with agar solution only. After 15 days, fruit were examined for development of disease symptoms, and examination continued until fruit maturation (late July). Approximately 20 to 50% of the inoculated fruit displayed discoloration or necrosis of internal tissue, particularly the pericarp and the embryo, although symptoms were more limited than those typically seen in fully expressed BAN and GN. No differences in symptoms were evident among the isolates tested. The controls showed no symptom development initially, although 5% began to develop discoloration at fruit maturity. Fungal isolates used as inoculum were reisolated from all symptomatic fruit by surface disinfesting tissue from the margins of necrotic lesions. For each isolate, the conidial characteristics were described from cultures grown under defined conditions (4). Three distinct groups of isolates were identified. Alternata sp. group isolates produced conidial chains (8 to 20 spores) with numerous secondary and occasionally tertiary chains branching from apical and median cells. Conidia were typically ovate and often possessed a one-celled apical extension. Tenuissima sp. group isolates developed conidial chains (10 to 22 spores) with occasional branching forming secondary chains from apical and median cells. Conidia were ovate to obclavate, often with long apical extensions (10 to 35 µm). Arborescens sp. group isolates developed conidial chains (5 to 12 spores) with numerous secondary, tertiary, and quaternary short chains branching from apical cells. Conidia were typically ovate with minimal apical extensions. Of the walnut isolates, 12, 4, and 3 were from the arborescens, alternata, and tenuissima sp. groups, respectively. Of the hazelnut isolates, 7, 6, and 3 were from the arborescens, alternata, and tenuissima sp. groups, respectively. The finding that Alternaria from several distinct sp. groups can cause similar disease on a single host is consistent with previous work on pistachio, almond, and pear (4). References: (1) A. Belisario et al. Plant Dis. 83:696, 1999. (2) A. Belisario et al. Plant Dis. 86:599, 2002. (3) A. Belisario et al. Inf. Agrario 59:71, 2003. (4) B. M. Pryor et al. Phytopathology 92:406, 2002.