Alternaria-, Fusarium- ja Venturia-itiöden runsaus ilmassa

Authors

• J. E. Hårdh Puutarhantutkimuslaitos, Piikkiö
• M. Sulkinoja Puutarhantutkimuslaitos, Piikkiö

DOI: https://doi.org/10.23986/afsci.71449

Abstract

The spore content of orchard air was determined in 1956—1957 at the Horticulture Research Institute by means of a Hirst spore trap (5). The spore countings were performed according to the Instruction leaflet given by the manufacturer of the spore trap. In 1956 the spore trap was in action from the 10th of May to the 5th of July, 24 hours a day. In Figure 2 the rainy days, amount of rain temperature, relative air humidity and the spore content in the air are given. Apple scab spores were discharged for the first time 13.5. In the air the first spores were detected 20.5. The last spores were discharged from the leaves 22.6., in the air spores were seen until the 4th of July. The maximum rate of apple scab spores in 1956 was 340 spores/m3. In 1957 the first spores were discharged 18.5., the last ones 16.7. In the air spores were detected from 18.5. to 6.7. (Fig. 3). During the primary infection period apple scab spores seem to be prevalent in the air every rainy day and, in addition, 2—3 days following a heavy rain. In 1957, thus, rain beginning the 10th of June at 4 o’clock and ending the 11th of June at 9 o’clock, produced only a slight spore content (Fig. 5), the rate of Venturia spores reaching, however, its maximum within 7 hours after the rain had stopped. 2850 spores/m3 were, then, counted. The last spores in the air were identified 32 hours later. Venturia inaequalis ascospores are prevalent in the air mainly during daylight, this fungus belonging to the 'day spore group’ described by GREGORY (3). A timing of sprays is being applied in most of the fruit growing areas in Finland in order to control apple scab. The beginning of the primary infection period and the end of it is being determined by the ’scab observers’ in accordance with the first and last discharge of spores from the overwintered apple leaves (7). It is assumed that differences between the data on ascospore discharge and the spore content in the air may not cause trouble in the timing of sprays, since the number of spores at the beginning and at the end of the primary infection period is small. In addition, spores probably carried over by the wind from rainy areas do not cause infection in an orchard where the apple leaves are dry. The content of Alternaria spores in the air does not seem to be influenced by rain or other weather conditions. Fusarium spores, on the other hand, were most abundant on rainy and warm days. High temperature seems to promote the spread of Fusarium spores more than that of Alternaria and Venturia spores (Fig. 2 and 3).