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Evaluations of Insecticides Against Leafhoppers: Summer 2021 Results

plastic cup with a layer of brown soil at the bottom and a green leaf in inserted in the end of a water filled tube on top of the soil

Written by Louis Nottingham and Katlyn Catron, August 9, 2021

Introduction

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
Methods

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
Methods

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.

Conclusions

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.

Acknowledgements:

Thanks to our funding from the Washington Tree Fruit Research Commission (Cherry), Oregon Sweet Cherry Commission, Corteva and Gowan for support of this research.

Contact

Katlyn Catron
Postdoctoral Research Associate
WSU TFREC
katlyn.catron@wsu.edu

 

 

 

 

 

Louis Nottingham
Research Assistant Professor
WSU TFREC
louis.nottingham@wsu.edu

 

 

 

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.

Pre-Harvest Pear Phenology Update

graphs showing the current pear phenology (adult and egg, blue; early nymph yellow; old nymph orange) for three sites: cashmere, Hood River and Wapato, and Medford

Pear Phenology Update, August 9, 2021

Pear Psylla’s Current Status:

The 2nd generation of summerform adults are at or past peak in most regions. Young nymphs of the 3rd generation are nearing peak and increasing. Hardshells of the 3rd generation are within the first 25% and rising. If biocontrol is present in orchards (IPM and organic orchards) the nymphs of the 3rd generation will likely remain below injury level without need for further management.

graphs showing the current pear phenology (adult and egg, blue; early nymph yellow; old nymph orange) for three sites: cashmere, Hood River and Wapato, and Medford

Graphs: Pear psylla life stages (curves) by degree days (x-axis) for three pear growing regions. Each life-stage curve shows relative abundance of the total predicted population. Adults and eggs are combined because the summer generations occur almost simultaneously. The vertical line represents Aug 8, 2021.

Pear Psylla IPM Recommendations (by Category):

  • Particle Films: Due to the proximity to harvest, it is not recommended to spray particle films. Additionally, particle films can increase pressure from spider mites and rust mites.
  • Honeydew Washing: Nymph numbers are increasing; honeydew washing may be necessary in the next 1-2 weeks, targeting 3700DD (between early nymph and hardshell peak). Scout weekly looking for dripping leaves and wash as necessary to remove honeydew.
  • Summer Pruning (“suckering”): Manually removing vegetative shoots is an effective way to remove psylla nymphs and improve spray coverage. However, this tactic can be risky at this point in the season due to the potential for sunburn. If you choose to summer prune, consider lighter pruning (20-50% shoot removal). Have pruners select shoots with the most honeydew to remove as much psylla and potential injury as possible.
  • Psylla Insecticides:
    • Conventional: The optimal time to spray (if necessary) is at 3500DD when young nymph are at peak, which will occur within the next 1-2 weeks, depending on your region. Choose a material that has low potential to disrupt natural enemies and offers some systemic action such as Admire Pro (imidacloprid) or Actara (thiamethoxam). Be mindful of your harvest time and the PHIs of each material.
    • Organic: Most organic orchards should have adequate biological control to make spraying for psylla unnecessary at this point. If this is not the case, the two most effective materials for psylla are neem products (Aza-Direct, Neemix, Rango) and Cinnamon oil (Cinnerate). These products can be safely mixed to increase efficacy and they are still unlikely to harm natural enemies. Be aware that either of these products can pool at the calyx end of fruit causing a ring. This seems to be related to spray volumes around 200 gpa, so it is important to calibrate sprayers to avoid this marking. Do not use neem product on Comice due to phytotoxicity.
  • Spider Mites:
    • Conventional: Many people have been battling mites all year. It is important to remember that mites are induced by over-spraying broad spectrum insecticides and miticides or particle films. In the future, follow soft or organic spray programs to avoid this issue. Soft materials that are still (relatively) effective against spider mites include Nealta, Onager, Apollo, and Acramite; Vendex. Envidor, Agri-mek, and Zeal are moderately soft. Other products that may still be effective but are less selective are FujiMite and Nexter. Be sure to check PHIs of any material selected.
    • Organic: Organic options for mite control are limited, but mites are often less of a problem in organic orchards due to biocontrol. Mites can be flared by some organic materials such as particle films or spinosad products like Entrust. Cinnerate and Rosemary oils (TetraCurb, Ecotec and others) help suppress spider mites with minimal non-target effects.

Codling Moth:

Codling moth is more of a challenge in further south regions and when more apples are present. If you are in a region that primarily grows pears and is cooler, codling moth is probably easily controlled with mating disruption, oil and 1 or 2 Altacor applications. If your pressure is high, you may need to include additional sprays, but they can still be soft. Consider using virus (Cyd-x HP) for mid to late summer sprays. Soft codling moth programs are much more effective when coupled with mating disruption, so if you are not currently using it, consider doing so next year.

collage of four photos showing closeups of "derry" psylla predator, ladybugs, lacewing eggs and trechnitesNatural Enemies:

Keep an eye out for natural enemies in your orchards (check out this beat tray sampling tutorial: https://www.youtube.com/watch?v=y-kXrHh0MP0). If you can find at least 1 natural enemy in 10-15 taps, you likely have better biological control than you realize. These predators and parasitoids will control your psylla and mites for free, so try to conserve them by using soft spray materials and avoiding unnecessary sprays.

Funding and Acknowledgements: This project is funded by the Fresh and Processed Pear Committees of Washington and Oregon and a WSDA Specialty Crop Block Grant. The psylla model was developed by Dr. Vince Jones. Model visualization graphics are being performed by Dr. Robert Orpet. Thanks to Dr. Rebecca Schmidt-Jeffris and Tianna Dupont for data and help with recommendations.

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.

 

head shot of a smiling man with dark hair wearing a dark suit with a white shirt and striped tieWritten by:
Louis Nottingham, Ph.D.
Research Assistant Professor
Dept. of Entomology, WSU TFREC, Wenatchee WA
louis.nottingham@wsu.edu

Psylla Sampling Instructional Video

How to Sample for Pear Psylla Using Beat Trays

Louie Nottingham demonstrates how to sample for pear psylla using the tray tap method, also known as the beat tray method.  You will need an 18″ x 18″ beat tray (DYI or available for purchase at some ag chemical companies), a tapping stick and a sampling plan for your orchard.

Principal Investigator or CFO?

June 22, 2021

Principal Investigator or CFO? Unpacking the PI Conundrum with Basic Economic Theory

by Louis Nottingham

This article was originally published in the Summer 2021 edition of “American Entomologist”
https://doi.org/10.1093/ae/tmab028

As a relatively new research faculty member, coming to grips with the true nature of running a lab has been something of an existential pursuit. The transition from researcher in- training (graduate student, then postdoc) to principal investigator (PI) has entailed a dramatic and unexpected shift in duties. During my graduate student and postdoc years, most day-to-day activities were tied directly to research projects, as expected, but as a PI, the amount of “investigating” I do is almost laughable. Instead, my tasks mostly revolve around grant applications, budget management, and administrative duties that ensure that the people who actually do the research in my lab remain employed. It’s ironic that after completing my research training, I largely stopped performing research. I spend a fair amount of time assessing my situation (i.e., anxiously spiralling) and trying to decide whether this outcome is a personal failing or the inevitable result of “climbing the ladder.”

So, where does any forlorn millennial turn for perspective on their first world woes? A podcast, obviously—but, less obviously, an economics podcast.

For many years, I’ve been a big fan of the NPR podcast Planet Money, which is informative and surprisingly funny. (Yes, economics can be funny.) In it, I see a lot of parallels between economists and entomologists: both groups are total nerds obsessed with important topics that few others care about, and we similarly like to use jargony “principles” to explain things. For example, if you found yourself in a group of economists and entomologists, the economists might toss around phrases like “opportunity costs” and “causal inference,” whereas the entomologists might casually insert a “niche ENTOMOLOGY AND SOCIETY partitioning” here and a “trophic cascade” there.

It was in this fine podcast, full of jargon, that I found an overly generalized but acceptable way to compartmentalize my PI conundrum. Enter the principle of “comparative advantage.” This is the idea that a team succeeds by allocating tasks among team members based on relative skill level instead of maximum skill level. So, in a research lab, the PI (in theory) is more skilled than grad students and postdocs in the department of research, but the relative difference in skill is not critically large. In other words, students and postdocs can still crank out some pretty dang good research, as we all know. Meanwhile, PIs, especially those of us who are new to the role, may not be that awesome at administrative tasks and budgeting; however, if those tasks were given to inexperienced postdocs or students, it could be game over for the lab. Therefore, the PI’s comparative advantage is in finance and administration, not research. So, the PI deals with the bills; the postdocs use their skills. Thanks a lot, economics.

Although my foray into economic theory may be more cute than useful, I do think it exposes a potential shortcoming in the current research structure. Because the most experienced researchers (PIs) are forced to spend so much of their time chasing funding, managing budgets, and administering, I cannot help but wonder whether this results in suboptimal research output and less time spent training the next generation of scientists. Perhaps if research labs were less beholden to the competitive grant system, our duties would better reflect our training, and the principle of comparative advantage would be much less compelling.

Author’s note: To illustrate the economic theory of comparative advantage, this article and its figures use generalizations that do not reflect all labs. In other words, I understand that there are many graduate students who perform advanced experiments, postdocs who have impressive budgeting skills, and PIs who directly conduct research. This is just meant to be a fun and somewhat sarcastic narrative of my own experience.

Louis Nottingham (Louie) is research assistant professor of tree fruit entomology at Washington State University’s Tree Fruit Research and Extension Center, and the Pacific Branch representative for the Early Career Professionals (ECP) Committee. In addition to paying other people to do research, Louie enjoys hiking, mountain biking, backcountry skiing, birding, and other outdoor adventures with his wife, Molly, and his dog, Blackbird. Visit Louie’s lab website for contact and additional information: http://tfrec.cahnrs.wsu.edu/nottingham/

Pear Psylla Phenology Update

June 7, 2021

Pear Psylla’s Current Status: Old nymphs (hardshells) from the first generation are still present but declining. Summerform adults and eggs are rapidly building in cooler locations (Cashmere) and nearing peak at 1500DD in warmer ones (Medford). Early instar nymphs of the second generation are building in all locations, and will peak at 1750DD. Hardshells of the second generation are just starting in all locations.

Fig 1. Pear psylla life stages (curves) by degree days (x-axis) for three pear growing regions. Each life-stage curve shows relative abundance of the total predicted population. Adults and eggs are combined because the summer generations occur almost simultaneously. The vertical line shows where we are as of June 2, 2021. (Model created by Dr. Vince Jones. Graphic visualization by Dr. Robert Orpet)

Pear psylla IPM Recommendations (by Category):

 

Particle Films

A particle film should have been applied at 800DD, but if not, do so ASAP to help deter further egg-lay. Our experiments have shown that spraying particle films after egg-lay provides some control of nymphs, however, it is less effective than spraying before egg-lay. It is still early enough that particle films will not leave problematic lasting residues on fruit; however, past the first week in June there could be issues, especially for early harvested red pear varieties.

Conventional IPM Insecticides

Two Ultor sprays should occur after petal fall, one at 1000DD and a second 14 days later. If your populations are consistently above 1 psylla adult per tray, you can apply Ultor + Esteem together. Neither Ultor or Esteem will reduce adult numbers but will prevent nymph development. While it may not be immediately gratifying, this slow kill is much better for promoting natural enemies.

*Both Ultor and Esteem can only be used twice per season, and consecutive sprays cannot be applied less than 14 days apart.

Organic Management

Cinnerate and/or neem products (but no neem on Comice) are effective on psylla, but may need to be sprayed as tank mixes and repeatedly from 1000 to 2200DD (around July 1) to keep populations suppressed. Monitor populations to determine spray frequency and tank mixing needs. The goal is to keep your population at or below one psylla per tray. Stop spraying after 2220DD, because these products will not control hardshell nymphs.

Cultural Strategies

Two main cultural strategies can be used for pear psylla: 1. Summer pruning and 2. Honeydew washing.

Summer Pruning: The removal of vegetative shoots (water sprouts) from trees. This not only improves spray penetration, it can reduce the psylla population and amount of honeydew in trees if timed correctly. Aim for 20002200DD to maximize psylla removal. Summer pruning can occur later in the season at 3100DD as well, however, there is a greater a risk of sunburned fruit.

Honeydew Washing: The process of washing honeydew from trees by overhead sprinklers or airblast sprayer. This method is different from overhead irrigation because it is only used to remove honeydew (we highly recommend performing general irrigating with under tree sprinklers to reduce the risk of diseases). Because washing too often and for too long can cause disease issues, it is important to only wash when there is enough honeydew to cause injury. Wash near the end of the hardshell stage for each generation, around 1400, 3000, and pre harvest if honeydew is high. These timings are not exact, but research to determine thresholds and timings for washing is currently underway. If using overheads to wash, we recommend about 6 hours of runtime for a system delivering ~70 gallons of water per acre per minute. A nonionic surfactant like Regulaid can be mixed in halfway through the cycle to improve honeydew removal. For airblast sprayer washes, use at least 800 GPA for smaller trees, and increase gallonage with tree size; the goal is to make water run off all leaves.

Codling Moth

Remember, a soft codling moth program is critical to conserve natural enemies that control pear psylla. Mating disruption and first sprays should have already occurred by this point. Soft codling moth spray materials include: oil, granulosis virus, Intrepid (methoxyfenozide), Esteem (pyriproxyfen) and Altacor (chlorantraniliprole).

Natural Enemies

All the methods suggested above will have low impacts on natural enemies. Natural enemies like lady beetles (Fig. 2A), predatory bugs (Fig. 2B), and parasitoid wasps (Fig. 2C) are critical to prevent psylla and mite population explosions closer to harvest, and they do it for free! So avoid broad spectrum materials, especially multiple products at a time.

Fig 2. Natural enemies of pear psylla; i.e., your friends! A) Lady beetle feeding on psylla nymphs (L. Nottingham). B) Deraeocoris brevis feeding on psylla nymph (B. Higbee). C) Trechnites insidiosus parasitizing psylla nymph (R. Schmidt-Jeffris).

Dusky Slug in Field Corn and Soybean

dark brown slug on a green leaf

June 2, 2021

Ambient moisture causes methomyl residues on corn plants to rapidly lose toxicity to the pest slug, Arion subfuscus, Müller
(Gastropoda, Stylommatophora)

The carbamate insecticide methomyl is sometimes used to control slugs in field corn and soybean by foliar applications, but control outcomes in research trials and commercial operations have been mixed. In this study,
laboratory bioassays were conducted on dusky slug, Arion subfuscus Müller, a common pest of corn and soybean in the Mid-Atlantic United States, to evaluate residual toxicity of Lannate LV (methomyl) at low and high
concentrations corresponding to label recommended field rates, and if toxicity may be affected by ambient moisture or repellency to treated plants. Without wetting events, methomyl residues on corn plants caused 90–100% mortality of A. subfuscus for two days and 70–90% mortality for six days. When corn plants were briefly misted with ca. 0.3 cm of water 6 h after methomyl application, mortality was 36% 12 h after treatment, and 0 to 5% 24 h after treatment for both low and high rates. Repellency of A. subfuscus to corn plants treated with the high rate of methomyl was narrowly significant (P = 0.04) and low rate was not significant. These results suggest that high ambient moisture needed to elicit slug activity in the field also abates toxicity of methomyl residues, explaining why field control is usually poor despite high mortality in the lab.

Psylla Phenology and Recommendations

June 1, 2021

Pear Psylla’s Current Status:
Some old nymphs from the first generation are still present but declining. Summerform adults and eggs are building in orchards (about 25-30% of the peak population are now present). Adults and eggs will increase until the peak at 1500 DD. Early instar nymphs of the second generation are beginning (10-15% of total population are present). No late nymphs of the second generation should be present.

Pear psylla life stages (curves) by degree days (x-axis) for three regions. Each life-stage curve shows relative abundance of the total predicted population. Adults and eggs are combined because the summer generations occur almost simultaneously. The vertical line shows where we are as of May 26 2021. (Model created by Dr. Vince Jones. Graphic visualization by Dr. Robert Orpet)

Pear psylla IPM Recommendations (by Category):

Particle Films: If you have not applied a postbloom particle film yet, you can still do so to help deter egg-lay, but it should be done immediately because egg-lay is getting closer to peak. Our experiments have shown that spraying particle films after egg-lay provide some control of nymphs, however, it is less effective than spraying before egg-lay. It is still early enough that particle films will not leave lasting residues on the fruit.

Conventional IPM Insecticides: The first Ultor (spirotetramat) application may have already occurred, but it can still be made at this point if not. Perform the first spray now if you have moderate pressure (around 1 adult per tray on average). If you have consistently more than 1 adult per tray, you can apply Ultor + Esteem (pyriproxyfen, which is also a soft and effective codling moth material). Apply a second Ultor spray 14 days after the first if pressure remains high or increases. Neither Ultor nor Esteem will reduce adult numbers, so this should not be expected. Instead, they will prevent nymph development. While it may not be immediately gratifying, this slow kill has the benefit of providing food to grow predators while suppressing the psylla population.
*Both Ultor and Esteem can only be used twice per season, and consecutive sprays cannot be applied less than 14 days apart.

Organic Management: Now is an excellent time to use Cinnerate and/or neem products (but no neem on Comice) at high label rates. These products should be applied at least twice, if not 3 to 4 times during this generation; ideally, at least one spray would have already been applied. If adult pressure is moderate (around 1 adult per tray on average), either product alone may be effective, especially if a particle film was already used. If pressure is high (greater than 1 adult per tray), these products can be tank mixed to improve efficacy.

Cultural Strategies: Two main cultural strategies can be used for pear psylla: 1. Summer pruning and 2. Honeydew washing. Summer Pruning: The removal of vegetative shoots (water sprouts) from trees. This not only improves spray penetration, it can reduce the psylla population and amount of honeydew in trees, if timed correctly. Aim for 2000-2200DD, before the 3rd generation of adults have begun emerging and all psylla will be in nymph stage and on the shoots. Summer pruning can occur later in the season at 3100DD as well, however, there is a greater a risk of sunburned fruit. Honeydew Washing: The process of washing honeydew from trees by overhead sprinklers or airblast sprayer. This method is different from overhead irrigation because it is only used to remove honeydew (we highly recommend performing general irrigating with under tree sprinklers to reduce the risk of diseases). Because washing too often and for too long can cause disease issues, it is important to only wash when it is necessary. We recommend targeting old nymphs of the second and third generations, so 1600 and 3000 DD. But remember, there is no need to wash if you do not have a fair amount of visible honeydew. If using overheads, we recommend about 6 hours of runtime for a system delivering ~70 gallons of water per acre per minute. A nonionic surfactant like Regulaid can be mixed in halfway through the cycle to improve honeydew removal. For airblast sprayer washes, use at least 800 GPA for smaller trees, and increase gallonage with tree size; the goal is to make water run off all leaves.

Pear Psylla Phenology Update

May 18, 2021

A phenology model for pear psylla was recently developed by Dr. Vince Jones. This model predicts the relative number of pear psylla from each life stage occurring as degree days are accumulated. Below is a graph showing the psylla degree day model and the status of psylla development on May 6th 2021. Degree days were averaged among weather stations in Medford, OR, Hood River, OR, Wapato, WA and Cashmere, WA; the difference from the coolest to hottest location was approximately 110 DD.

Click the graph for the full article.

 

Evaluations of Conventional and Organic Insecticides Against Leafhoppers: First Year Results

May 18, 2021

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.

Click the graph for the full report.