Restriction of russet mite and influence on predatory mite dispersal using different stem barriers in tomato crop.

The tomato russet mite, Aculops lycopersici (Tryon), is a key pest of commercially grown tomatoes worldwide. Due to its minute size, its detection is often not timely for effective control. In this study, the approach of limiting A. lycopersici population growth by repeated application of barriers on tomato stems is tested. In potted plant trials, barriers of oils, oil formulations, insect glue, diatomaceous earth [DE] and adhesive tape [NT] impeded upward movement of A. lycopersici on tomato stems for several weeks as compared to the control. Iolinid mites have shown promising results for A. lycopersici control. Therefore, the selectivity of barriers regarding predatory mites was also tested, using A. swirskii as a model organism. Barriers with [NT] showed the best selectivity ([NT] > oil formulation >[DE], p < 0.05 for each day count of mites above barriers). However, application of [NT] seems challenging in a broader scale. Under greenhouse conditions with practical crop stands, regularly applied barriers reduced the percentage of symptomatic leaves for two weeks (oil formulation and [DE], variety Roterno, 2023 and oil formulation, variety Baylee, 2024, p < 0.05; in 2024 no significant reduction was found on Roterno and [DE] was not tested). The comparison of different varieties showed less effect of barriers in the variety Roterno with more upward facing leaves, indicating that leave angle affects overcoming of barriers by A. lycopersici. The fact that under greenhouse conditions this control effect did not cover the whole season reduces the practical applicability of the method. Under similar conditions, an earlier study reached longer lasting control using insect glue as a barrier substance. Possible reasons for the discrepancy between studies include differences in tomato varieties, barrier positions and pest densities.