Acaricidal Control of Broad Mites in Blackberry, 2016

Polyphagotarsonemus latus (PL) is an emerging pest of primocane blackberries in multiple states in the United States. The objective of this study was to evaluate the relative efficacy of Agri-Mek (standard) to several miticides against PL. Currently, Agri-Mek® SC is the standard and only miticide labeled for blackberries against PL. Leaf dip petri dish bioassays were conducted at the laboratory of the University of Arkansas Southwest Research and Extension Center (SWREC) in Hope, AR. Treatments each were replicated five times and arranged in an RCB design. On 25 July 2016 (Table 1), and 25 August 2016 (Table 2), PL-infested blackberry leaflets were collected from the first fully opened terminal leaflets of established ‘Prime-Ark® Freedom’ blackberry plants maintained in the field under a high tunnel at the SWREC. A stereomicroscope was used to scan underside of leaflets and select those with similar numbers of live PL of all stages. Thin sponges were placed in petri dishes, kept moist with distilled water and covered with a Kimwipe* (Kimberley-Clark). Treatment solutions listed in Tables 1 and 2 were prepared in distilled water. Each leaflet was dipped and gently swirled for 5 s in a treatment solution, air dried for 30 min on paper towels, and placed underside up on the moist sponge in a petri dish. The petiole was covered with a moistened Kimwipe, dish cover set in place and maintained at 25°C. At 1 and 3 DAT, a stereomicroscope was used to aid in counting the number of each PL stage within a 2.4-cm² leaf area (1.27 × 1.9 cm) centered over the leaf midrib. Nymph and adult PL were recorded as the numbers of mobile or mordid (no walking or motion within 5 s of observation so presumed dead). The immobile quiescent nymph was not counted. Percentage mortality data were arcsine square-root transformed prior to the ANOVA and Tukey’s studentized range test (HSD) (P ≤ 0.05) to distinguish treatment mean differences. Actual non-transformed mean percentages are presented in these tables.

In trial 1 (Table 1) at 1-DAT, Agri-Mek, M-Pede, Microthiol, and 1% Trilogy all caused > 88% Pl larvae mortality similar to that by 2% Trilogy and 2% JMS Stylet Oil but significantly greater than that by 2% JMS Stylet Oil (33.6%) and the water check (15.6%). Agri-Mek, both rates of M-Pede and Trilogy and 2% JMS Stylet Oil all killed >63.3% which were significantly more effective than Microthiol, 1% JMS Stylet Oil and the water check that were all similar (<59.3%). By 3-DAT, all treatments, except 1% JMS Stylet Oil, caused significantly more mortality of Pl larvae (>77.2%) and adult Pl females (>68.7%) than did water check (<50.6 and 60.1%, respectively).

In trial 2 (Table 2) at 1-DAT, Agri-Mek killed 98.5% larvae and 100% adult Pl females which were similar to the 53–56% Pl larvae mortality by 4% Quillaja and Movento but significantly higher than the other treatments that killed <40.6% Pl larvae and <38% adult Pl females. By 3-DAT, Agri-Mek killed 100% of Pl larvae and 100% adult Pl females. These percentages were similar to that for 4% Quillaja treatment and both rates of penetrate that all caused >69.1% Pl larval mortality whereas both rates of Quillaja and 4% penetrate killed >76% adult Pl females. By 3-DAT (Tables 1 and 2), Agri-Mek, 1 and 2% M-Pede, 10 lb and 15 lb Microthiol, 1% Trilogy, 2% JMS Stylet Oil, and 4% Quillaja all caused >83.6% total Pl mite mortality. Therefore, these formulations could be recommended for use in rotation with Agri-Mek® for PL control in blackberries. This research was supported by industry gift(s) of pesticide and/or research funding from Southern Region IPM Small Fruit Consortium/IR-4 Performance Program No. 2016 R-07.

Author notes