Colladonus reductus leafhoppers were collected from organic or unsprayed orchards’ groundcover (Fig. 1) via sweep nets, then returned to the lab. Leafhoppers were exposed to insecticides by direct sprays or previously treated leaves from cherry trees. After exposure, leafhoppers were kept in ventilated arenas with treated cherry leaves (Fig. 2) for 24-48 hours, then rated as alive or dead. Between 25-50 leafhoppers were examined per treatment in each experiment.
Combined 2020 & 2021 Results:
Columns show average percentage mortality (dead ÷ total x 100) from each insecticide and exposure type. Values above dotted line are averages from at least two trials; below are from a single trial.
2021 Particle Film and Oil Repellency Trial
By Dr. Louis Nottingham and Dr. Katlyn Catron
Leafhoppers were collected from orchard groundcover and returned to the lab. Forty leafhoppers were added to cages with leaves treated with either H20, IAP oil 1%, Surround WP (kaolin) 50 lb/acre, or Celite (diatomaceous earth) 50 lb/acre (Fig. 3). Four experiments were conducted. In the first two, Surround and Celite were mixed with 1% oil, in the second two, no oil was mixed with these two products. Two visual evaluations were conducted for each experiment, (5 hours and 24 hours after treatment) to determine how many leafhoppers occupied each leaf.
Leaves treated with Surround or Celite had the fewest leafhoppers, followed by 1% Oil (Fig. 4). Some leafhoppers were found on Surround, and Celite treated leaves, generally in areas with less or no particle film residues. Although particle films demonstrated significant repellency in this test, more testing is needed to understand if particle films or oil can reduce the spread of x-disease phytoplasma.
Funding: Thanks to the WA Tree Fruit Research Commission and OR Cherry Groups for research funding.
**Use pesticides with care. Apply them only to plants, animals, or sites listed on the labels. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions; it is a legal document. Always read the label before using any pesticide. You, the grower, are responsible for safe pesticide use. Trade (brand) names are provided for your reference only. No discrimination is intended, and other pesticides with the same active ingredient may be suitable. No endorsement is implied.
Written by Louis Nottingham and Katlyn Catron, August 9, 2021
Data showing efficacy of insecticides against leafhopper vectors of x-disease is still relatively sparse. To address this, we performed two lab bioassays to screen insecticide products against Colladonus montanus reductus, the most abundant leafhopper vector of x-disease found in Washington cherries. We evaluated insecticides in both direct-spray and residue decline experiments to assess the immediate and longer-term efficacy of these products on the leafhoppers.
Contact Spray Lab Bioassay – 2021
Leafhoppers (C. reductus) were collected from weedy row middles in an organic commercial apple orchard bordering a conventional cherry block and returned to the lab for processing. They were sorted into bioassay arenas composed of an 8 oz plastic deli cup with a layer of moist soil on the bottom, an excised cherry leaf, and a lid with a plastic mesh cutout to allow for application of treatments and air circulation (Fig. 1). Approximately six leafhoppers were placed into each assay arena, then treatments (Table 1) were applied through the mesh cutout on the deli cup lid using a hand-pump aluminum spray bottle. Five replicates per treatment were completed. Assay arenas were moved to a greenhouse for 24 hours before mortality was evaluated.
Results and Discussion
All products provided significant control compared with the check, and were statistically similar (Table 2). Numerically, the group 4A (neonicotinoid) insecticides, Admire Pro and Actara, provided the highest efficacy at or near 100% mortality. The group 4C insecticide, Transform, also provided high efficacy at 90% (± 3.7%). Magister, a 21A METI, was on the lower range for these products, at 80% mortality. This was the first evaluation of Magister against leafhoppers, so additional testing is needed before recommendations are made.
Insecticide Residue Bioassay
To evaluate the longer-term efficacy of several insecticides, potted cherry trees were treated with insecticide products (Table 2) using hand-pump aluminum spray bottles. Trees remained exposed to outdoor ambient conditions, including sunlight and occasional rain, for the duration of the experiment. Treated cherry leaves were excised at predetermined intervals, after 0 h (fresh residues), 72 h (3 days), 168 h (7 days), and 336 h (14 days). After excision, leaves were placed in arenas as described in the Contact Spray Lab Bioassay above (Fig. 1), and approximately six C. reductus adults were exposed to the aged residues per replicate (3-5 replicates per treatment per time interval). After 24 hours, mortality was evaluated.
Results and Discussion
C. reductus mortality after exposure to fresh insecticide residues ranged from 88.3% in the Pyganic (pyrethrins) treatment to 100% in the Actara (thiamethoxam) treatment (Fig. 3). Mortality in leafhoppers exposed to Actara remained higher than 80% even after two weeks (336 h) of residue aging outdoors. In the Asana (esfenvalerate) and Pyganic treatments, leafhopper mortality dropped considerably after 72 h of residue aging, with neither insecticide causing greater than 60% mortality when aged. Pyrethroids are notoriously unstable when exposed to UV light, which explains the reduced efficacy of Pyganic after treated leaves were exposed to outdoor conditions for 72+ hours. Asana provided slightly better control after 72+ hours of residue aging, which may be due to its oil-based formulation specifically designed to withstand UV rays and rain wash-off. Regardless, Actara provided the highest levels of control for the longest periods of time in this bioassay.
The results from these trials will inform future insecticide work with leafhopper vectors of X-disease in Washington. In the next year, additional products will be screened in both direct-spray and aged residue bioassays to help form a more complete picture of control methods available to and effective for growers. Furthermore, other economically relevant species of leafhoppers will be incorporated into similar trials to assess their susceptibility to these insecticides.
Thanks to our funding from the Washington Tree Fruit Research Commission (Cherry), Oregon Sweet Cherry Commission, Corteva and Gowan for support of this research.
Use pesticides with care. Apply them only to plants, animals, or sites listed on the labels. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.
YOU ARE REQUIRED BY LAW TO FOLLOW THE LABEL. It is a legal document. Always read the label before using any pesticide. You, the grower, are responsible for safe pesticide use. Trade (brand) names are provided for your reference only. No discrimination is intended, and other pesticides with the same active ingredient may be suitable. No endorsement is implied.
Prior to this project, there was no available experimental information on insecticide toxicity against the leafhopper X-disease vectors Colladonus Reductus and C. geminatus In 2020 we performed lab bioassays to screen various insecticide products against the most abundant of these two species in Washington cherries, C. reductus. Five insecticide materials achieved 100% mortality of C. reductus: 3 conventional and 2 organic. We will continue these screenings in 2021, with added focus on residue degradation and strategic spray timings.
First generation adults from leafhopper vectors of X-disease phytoplasma including C. reductus and C. geminatus started being found in traps the week of May 10, 2021. Generally, second generation leafhoppers are of higher concern as first generation leafhoppers are often controlled by your standard insecticide program. To review your current insecticide applications for efficacy against leafhoppers see http://treefruit.wsu.edu/crop-protection/disease-management/western-x/
Leafhopper Deterrence Linked to X Disease Management
WSU entomologists and industry partners learn about X disease vectors to help the cherry industry optimize management. Work by the Nottingham lab on insecticide efficacy (“catching lots of wild leafhoppers and trying to keep them alive long enough to kill them”) and systemic insecticides applied via soil drench is highlighted.