Monitoring of spruce spider mite (Oligonychus ununguis) populations in field-grown ornamental cedars and characterization of entomofauna in this environment

By: IQDHO Plant Health Monitoring Team

One of the major pests affecting ornamental cedars is Oligonychus ununguis (spruce spider mite). It feeds on the chlorophyll of twig cells, causing them to turn yellow and discoloured.

In 2019 and 2020, a project was conducted to develop a screening method for O. ununguis in field-grown ornamental cedar by attempting to correlate a simple method (shaking) with a more extensive method (brushing cedar twigs with a mite brush). The project also aimed to characterize spruce mite population curves during the cedar growing season.

During the 2019 season, entomofauna related to O. ununguis was also studied. Organisms observed included two predatory mites, Anystis baccarum and Typhlodromina citri, and the phytophagous mite Platytetranychus thujae, which was relatively abundant during this summer. In 2020, monitoring of Platytetranychus thujae populations and a study of mites and predators occurring at the same time as spruce spider mites were conducted to better identify which mites cause damage to cedars and the natural enemies of the pest mites present in the same environment.

At the end of these two years, a comparison of the shaking and brushing techniques revealed that shaking provides a relatively accurate estimate of O. ununguis and P. thujae populations.

The phytophagous mite Platytetranychus thujae was present in very large numbers in 2020 in the cedars of one grower. This phytophagous mite may be present in many cedar groves in Quebec, but it is likely to be confused with O. ununguis. It would be interesting to know if this mite behaves exactly like O. ununguis, causing the same damage at the same population density, or if it behaves differently.

This project was carried out as part of the activities of the Réseau Pépinières Ornementales, of the Réseau d’avertissements phytosanitaires, with financial assistance from the Ministère de l’Agriculture, des Pêcheries et de l’Alimentation.

For more details, please refer to the project reports: