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Abstract

We evaluated the effect of selected insecticides on 6 mature Shademaster honey locust trees (Gleditsia triacanthos L., ‘Shademaster’) which were planted in 2 rows along a roadside on the University of Kentucky’s campus. We used a randomized complete block design where each tree represented a block, and within each tree, the effect of insecticides on scales was evaluated on separate labeled branches. All trees had been heavily infested with calico scale (CS) for multiple years. On each tree we sectioned off 11 randomly selected 30-cm branch sections with zip-ties. We applied treatments on 28 May 2024, when CS crawlers were emerging. We applied all products to the branches and both sides of all leaves following labeled rates using separate Chapin 2000 handheld pump sprayers pressurized to 60 psi with a hollow-cone nozzle. The volume of each application was approximately 121 ml. All treatments were applied on 0 and 14 DAT, while treatments 3–7 were also re-applied 7 DAT. We recorded settled crawler density across 2 randomly selected leaves and all leaflets attached to these leaves per treated branch. For collections at 3,7,14, and 28 DAT, we cut all leaves in half to reduce the amount of time needed to count scale crawlers due to the high densities found on sampled leaves and leaflets. One sample on 3 DAT (T5—Tetracurb Max, replicate no. 4) was lost in the process of transferring it from the field to the lab. On 0 DAT, we only recorded total CS density and did not separate living from dead scales. On all other sample dates, we recorded total, living, and dead CS density. We took photos of all leaves against a white background with a ruler in the image to calculate the area over which CS were counted using ImageJ software. We recorded phytotoxicity on all leaf photos and ranked discoloration on a scale of 0–10, where 0 indicated minimal discoloration and 10 indicated leaf death. We square-root transformed scale density (counts/cm2) and used type-II ANOVAs and follow-up Tukey HSD tests to determine if total, living, and dead CS density varied across treatment within each sampling period. We ln(x + 1) transformed phytotoxicity rankings and used type-II ANOVA and Tukey HSD tests to determine if phytotoxicity varied across treatments within each sampling period.

Document Type

Article

Publication Date

6-13-2025

Notes/Citation Information

Wilson, C.J. and York, Z.K., 2025. Effect of selected insecticides on calico scale in landscape honey locust trees, 2024. Arthropod Management Tests, 50(1), p.tsaf099.

Digital Object Identifier (DOI)

https://doi.org/10.1093/amt/tsaf099

Funding Information

This research was funded by the IR4 project and made possible by industry gift(s) of pesticides.

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