Effect of weather on the abundance of winter eggs of the European red spider mite on apple

Authors

• Tuomo Tuovinen Agricultural Research Centre of Finland, Institute of Plant Protection, SF-31600 Jokioinen, Finland

DOI: https://doi.org/10.23986/afsci.72431

Abstract

Winter eggs of the European red spider mite Panonychus ulmi were counted on apple twig samples (N = 279) collected in south-western Finland in the winters of 1984/85 through 1989/90. The results of the counts were analyzed to determine the effect of the regional temperature and precipitation during the preceding growing season on the abundance of overwintering spider mite eggs. The total effective temperature sum of the growing seasons in day-degrees over + 5 °C varied between 1030 and 1564 and the total precipitation between 289 and 562 mm in May - October. The number of P. ulmi winter eggs in commercial orchards correlated positively with the sum of day-degrees in August, July, June and during the entire growing period. There were negative correlations between the numbers of P. ulmi winter eggs and the precipitation in May, October, August and in the entire growing season. The cold winters of 1985 (min. temp. - 36.7 °C) and 1987 (- 34.0 °C) reduced the percentage of winter egg hatching to 23 and 56.5 %, respectively, compared to the mean hatching rate of 75-77 % in 1986 and 1988. The value of weather records to facilitate the prognosis of need of early spring sprays against P. ulmi is discussed.