Treatment Thresholds for Tetranychus pacificus

• Published in: Journal of economic entomology 2021-08, Vol.114 (4), p.1834
• Main Authors: Haviland, David R, Rill, Stephanie M, Gordon, Chelsea A
• Format: Article
• Language: English
• Subjects: Almond; Analysis; Biological control; Decision-making; Pests; Thrips
• ISSN: 0022-0493
• DOI: 10.1093/jee/toab110

Optimization of integrated pest management for Pacific spider mite, Tetranychus pacificus McGregor, in California almonds requires that miticide applications be delayed as long as possible to promote biological control, while still occurring before exponential mite increases cause defoliation. We used data from twelve untreated almond orchards between 2006 and 2019 to determine that decisions to treat T. pacificus should be made on the first monitoring date with 1.4 mites per leaf (38.1% of leaves infested) to ensure that miticide applications are made prior to reaching the treatment threshold of 5.4 per leaf an average of 4.7 d later. Modifications to this threshold based on biological control were made using capture rates of sixspotted thrips, Scolothrips sexmaculatus Pergande, on yellow adhesive traps from 14 almond orchards between 2016 and 2019. Data showed that T. pacificus density remained unchanged when there were 0.42 S. sexmaculatus per trap per week for every one T. pacificus per leaf. For orchards where T. pacificus density has exceeded action and treatment thresholds, we developed a less accurate, but more practical, model that does not require counting mites on leaves. On average, T. pacificus density remained unchanged for seven and 14 d if there were an average of five and three S. sexmaculatus per trap per week, respectively. Growers who adopt the action and treatment thresholds presented herein have the potential to avoid unnecessary miticide use, maximize reliance on biological control, and promote the long-term sustainability of California's almond industry. Key words: IPM, decision-making, threshold, predator-prey ratio