Storage fungi of onion and their control

Risto Tahvonen

doi:10.23986/afsci.72053

Abstract

Botrytis allii Munn caused total onion damages of 15—20 % during storage in 1975—1979, and was present on 80—90 % of the spoilt onions. The proportion of damage caused by Fusarium oxysporum Schl. was 0—5 % and was present in 0—10 % of the spoilt onions. The early weight losses during storage of the onions were mostly due to storage pathogens which spread via the onion sets used as propagation material. This can be prevented very effectively by soaking the sets in benomyl solution before planting out. The unusually high fungus content of the sets resulted in a reduced yield. Spraying with fungicide early on in the growing season and applying different amounts of nitrogen fertilizer had no significant effect on the number of storage pathogens. A low stroge temperature did not inhibit the development of storage pathogens, it merely slowed it down.

Highlights

During the last few years, 500—600 ha have usually been under onion cultivation in Finland, Since the Finnish growing season is short, onion sets, which are almost completely of foreign origin, have to be used for onion cultivation
B. allii was usually found in 80—90 % of the completely spoilt onions (Table 1)
In the preliminary trials carried out in 1976, B. allii inoculated on healthy onions grew at temperatures below O°C, but F. oxysporum only caused onion spoilage at temperatures above O°C (POHTO 1979). The results of these experiments show that Botrytis allit, which was clearly the most serious storage pathogen of onions, primarily spreads to the onion crop via the sets

Summary

Introduction

During the last few years, 500—600 ha have usually been under onion cultivation in Finland, Since the Finnish growing season is short, onion sets, which are almost completely (about 85 %) of foreign origin, have to be used for onion cultivation. In countries to the south of Finland, onions to be stored are grown from seed and the occurrence and spread of storage pathogens in Finland is likely to be different from that elsewhere. According to information provided by onion growers, storage pathogens have caused total onion losses of as high as 50—60 % in modern cold stores. For this reason, storage pathogens are considered to be one of the most serious problems in onion growing. Right up until a few years ago, Botrytis allii Munn, which is the most important storage pathogen of onion, was reported to infect onions in the field, usually close to harvesting time or during harvesting in Finland (jAMALAINEN 1962) and elsewhere (HEINZE 1974). A number of studies have shown that B. allii spreads to onions via the seeds and is dormant during the growing season (MAUDE and PRESLY 1977 a)

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