Epidemiology of pear decline in orchards without vector control in Southwest Germany

In the past decade, pear decline is spreading in Southwest Germany due to climate change and reduced insect vector control. Monitoring of nine old pear orchards revealed infection rates between 40% and 80%. The presence of ‘Candidatus Phytoplasma pyri’ was confirmed by PCR. In 2021-2023, all three known pear psyllid vectors were captured in various population densities. Winter forms of Cacopsylla pyri were infected between 0.4 – 4.4% while winter forms of C. pyricola had infection rates of 2.9 – 9.4%. The univoltine species C. pyrisuga was scarcely captured with only one infected individual. C. pyri and C. pyricola transmitted the phytoplasma to healthy test plants, but quantitative PCR data indicated that only about 40% of infected individuals of both species had sufficient high phytoplasma loads to be regarded as infectious. As both species are very abundant in orchards without insect vector control, spread of pear decline is high.