Climate trends in the Lake Constance region and challenges to pest management programs from a consultant's perspective


Abstract: While annual climatic data from Lake Constance area only show a slight increase of maximum and decrease of minimum temperatures, precipitation has decreased by about 30% in the past 23 years. Calculated on a monthly basis a remarkable increase of average temperatures up to 2 °C and maximum values up to 4 °C in April, May, June, September, October and November have been recorded, while January March, July and August show a decrease. Leaf wetness hours increased by up to 40% in August, September and November, while a 20% decrease has been observed in April. Precipitation decreased by approx. 40% in April and June and 50% in November while July and August show an increase of approx. 30% and 40%, respectively. Despite no significant changes in average, maximum and minimum temperatures on a monthly basis have been recorded in February, bud burst since the early 1990s in about 50% of the years occurred about three weeks earlier than before, caused by high heat units being calculated for February of those years. The changes in temperatures enabled the production of varieties requiring high temperatures especially in May and June, while others cannot be produced any more or exhibit sunburn and show poor coloration because of too high temperatures in September. In apple scab control a severe change from regular rainfalls to only showers, which in many cases do not occur at all, leads to very high percentages of ejectable ascospores for several weeks, resulting in an increased number of treatments. Predicted rainfalls, that – if at all – finally only occur as local showers, frequently result in a remarkable waste of fungicide sprays. The increase of leaf wetness hours in August and September resulted in improved infection conditions for apple scab but also for summer diseases. The most obvious effect on pests has been observed for codling moth, resulting in an earlier begin of the first generation. Dry spells accidentally distributed over the year and lasting up to 8 weeks that frequently occurred since 2003 are considered the most dangerous effect of a further increasing climate change, because a slight increase to approx. 10 weeks may destroy a high percentage of fruit orchards from acute water deficiency. The effects of climate change are expected also to generally be exacerbated by a decrease of agricultural research and advisory in common with structures in education and research preventing the build-up of experience and overview within individual crops.

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