No description available.

No description available.

Presented as Thesis (Ph. D.)--University of Wisconsin--Madison, 1929. / Cover title. Reprinted from Phytopathology, vol. XXI, no. 5 (May 1931). Includes bibliographical references (p. 520-523).

Thesis (Ph. D.)--University of Wisconsin, 1966. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

[...] Pour les raisons énoncées précédemment, il nous a semblé important d'étudier quelles étaient les réactions du champignon lorsqu'il venait en contact avec les substances naturellement présentes à la surface des feuilles, quelle était lat nature de ces substances et leur rôle dans l'établissement de la maladie et aussi comment une fois la maladie établie, le champignon pouvait affecter la nature et la quantité de ces substances qui sont perdues par les feuilles sous l'action de la pluie. [...]

No description available.

Disease management in organic apple orchards in Vermont is focused on controlling diseases with sulfur fungicides. The objective of this two year study was to evaluate the target and non-target effects of an organic disease management system containing agricultural biostimulants compared to two sulfur-based systems on foliar and fruit diseases, pest and beneficial arthropods, tree growth, yield and fruit quality on four cultivars, `Ginger Gold', `Honeycrisp' and `Liberty' and `Zestar!'. Trees were arranged in a complete randomized design of five three-tree replications in a certified organic orchard. The two sulfur-based systems differed in the number of applications; in the third system, sulfur was replaced with biostimulants including pure neem oil, liquid fish, an activated microbial inoculant plus equisetum and stinging nettle teas. Each biostimulant application also included kelp meal, unsulfured organic molasses and yucca extract emulsifier. The biostimulant system did not successfully manage apple scab and rust diseases as well as the sulfur-based fungicide systems, and had variable results with other diseases. No differences were observed among the three systems in tree growth parameters; however, the length of the study may not have been sufficient to determine effects. Differences in the incidence of disease among the three systems were reflected in extrapolated figures for gross income per hectare which takes into account fruit yield and quality. In the higher fruit-bearing year of the study, it was estimated that the gross income per hectare of the biostimulant system would be significantly lower than the reduced-sulfur system and the full-sulfur system by at least $5,800 and $12,000, respectively. In that same year, it is estimated that the full-sulfur system would have generated approximately $6,500 more gross income per hectare than the reduced-sulfur system suggesting the number of sulfur sprays can influence fruit quality and income. The use of the agricultural biostimulants had very limited non-target effects and when present, they were beneficial in suppressing insect pest incidence and/or damage on foliage compared to one or both of the sulfur-based fungicide systems. However, many insect pests or their damage were not observed on the foliage or had incidence of less than 1% in any of the systems. The biostimulant system did appear to suppress European red mites in both years compared to both sulfur-based systems when data were averaged across cultivars. On fruit, no differences in non-target impacts on arthropod pests were observed among the three systems except for surface-feeding Lepidoptera and San Jose scale damage. In a separate phytophagous mite study on the cultivar `Zestar!' leaf samples were evaluated for the number of motile phytophagous mites every 14 days from 1 July through 26 August each year. When there were differences, the biostimulant system had less mite incidence per leaf than one or both of the sulfur-based systems in both years. The difference in the number of sulfur sprays did not have a major effect on the mite populations. In summary, the use of the biostimulant system resulted in insufficient disease management which led to lower estimated gross income compared to the sulfur-based systems. These results show more research and further evaluation of new organic disease management tools, including the use of agricultural biostimulants, are necessary before growers consider replacing the use of standard sulfur fungicides for disease management in Vermont orchards.

In 1992, a research program was initiated to select suitable antagonists against the saprophytic (or winter) phase of the apple scab pathogen, Venturia inaequalis. An improved method for the mass screening of a vast collection of fungi was developed for this purpose. Some of the previously reported criteria such as leaf rheology and overwintering structure production proved unreliable or fastidious and cannot be used for in vitro antagonist selection. The main antagonism selection criterium retained was the in vitro inhibition of ascospore formation. To measure ascospore production, a simplified method of in vitro pseudothecia production was devised. This new method eliminates the need for prior conidia production by using a mycelial suspension and greatly reduces the risks of sterile mating by using a cocktail of Venturia inaequalis strains of different origins. Finally, the production cycle duration was reduced by varying the incubation temperature during the simulated winter. Moreover, a quick and efficient method of ascospore collection was developed. Ascospores were forcibly ejected in a large scale bubbler type apparatus in only one hour. This bubbler can be used for other studies including axenically produced ascospores. This new method compared favourably to the previously reported method and was used to screen a collection of about forty-two fungi. Six proved to significantly reduce the ascospore production of Venturia inaequalis. Two were as effective as Athelia bombacina, a previously reported antagonist of pseudothecia formation and inhibited over 98% of the ascospore production. These new organisms are now available for future field tests. Future selections from a large collection of saprophytes can now be based on a reliable and simple in vitro screening methodology.

Venturia inaequalis, the causal agent of apple scab, overwinters in apple leaves on the orchard floor. To develop a control strategy based on the prevention of the maturation of overwintering pseudothecia, a sampling of fungi colonizing dead apple leaves was conducted from different orchard floors in Quebec during the spring and fall of 1993. A total of 345 different isolates were obtained, from which fifteen genera have never been previously recorded as colonizers of apple leaves in North America. Small differences were detected in genera richness among orchards but the fungal composition of each orchard was fairly unique. Different tests on growth on amended media and leaf decomposition demonstrated that leaf degradation is not a reliable parameter alone to screen antagonist against V. inaequalis. No significant relation between growth on amended media, leaf rheology and ascospore inhibition was detected. However, 40 fungi reduced significantly ascospore production more than 87% compared to the control (V. inaequalis only). Of these antagonists, 30% decomposed apple leaves, suggesting that competition for the substrate is involved in the mode of action of at least one third of the antagonits detected. Other possible modes of antagonism are discussed.