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2018 Adult Pear Psylla Bioassays

By Louis Nottingham and Elizabeth Beers, WSU Entomology, TFREC

Psylla and mite bioassay results for early season sprays from Dr. Louis Nottingham and Dr. Elizabeth Beers. These results are part of a larger Pear IPM project. For additional results see http://treefruit.wsu.edu/crop-protection/pear-ipm/

Bioassay 1: slide dip exposure

This bioassay was conducted to test various conventional and organic products that are often used in early season sprays for the control of psylla and/or mites.

Note ** Dimethoate is very likely to be phytotoxic to pears! It was only included in the trial because it has systemic activity, and may be useful for postharvest sprays. Do not use this product at this time of year.

Methods

Psylla adults were collected from a commercial orchard in Dryden, WA. Psylla were returned to the lab where they were anaesthetized for sorting by sex. Only females were used. Adults were adhered to a microscope slide (10 per slide) using double sided tape. Adults are attached by their wings, so their legs are facing up. Slides with psylla attached were dipped in 500 ml of pesticide solutions (see Bioassay 1 Treatment List) for about 2 seconds, then allowed to dry. Each treatment was replicated 5 times.  Psylla were kept in a climate-controlled room at 22 °C and checked every 24 hours for living and dead psylla. Psylla are determined alive or dead by touching their legs with a soft paint brush, and gaging the level of response. Occasionally, psylla recover from what appears to be a dead state; hence, why sometimes mortality within a treatment decreases from one sample to the next.

Results

Dormant oil, Malathion, Dimethoate and Assail treatments resulted in high levels of mortality. Dormant oil produced 100% mortality at 24 hours, making it the fastest acting treatment. Lime sulfur produced intermediate levels of mortality. Wettable sulfur was no more toxic than water.

Bioassay 1: Treatment List

Trt. Product Rate/100 gallons Amt./ 500ml
1 Malathion 5EC 32 fl oz 1.25 ml
2 Dimethoate 4EC 32 fl oz 1.25 ml
3 Assail 70WP 3.4 oz 0.12 g
4 Lime Sulfur 7 gal 35 ml
5 Wettable Sulfur 15 lb 15 lb 9 g
6 Dormant Oil 4% 20 ml
7 Check (H20)

Bioassay 2: Potter spray tower

This bioassay used a Potter spray tower method to test various organic products against adult pear psylla. Cinnerate was tested at experimental rates, higher than what is listed on the label. Consult the label for current field rates.

Methods

Psylla adults were collected from the TFREC research orchard in Wenatchee, WA. Psylla were returned to the lab where they were anaesthetized for sorting by sex. Only females were used. Females were placed in small plastic cups (10 per cup) with a moistened cotton-round for humidity, and treated using a laboratory sprayer (see Bioassay 2 Treatment List). Each treatment was replicated 5 times. After treatment, adults were kept in a climate-controlled room at 22 °C, and checked every 24 hours for living and dead individuals.

Results

Cinnerate at the high rate, 60 fl oz/100 gal, was very effective from 24 hours and on. Lime sulfur was not immediately effective, but by 48 hours produced nearly 90% mortality. Cinnerate at the lower rate, 40 fl oz/100 gal, and Surround CF at 50 lb/100 gal had intermediate efficacy.

Bioassay 2: Treatment List

Trt. Product Rate/100 gallons Amt./ 500ml
1 Cinnerate 60 fl oz 2.35 ml
2 Cinnerate 40 fl oz 1.56 ml
3 Lime Sulfur 3 gal 15 ml
4 Surround CF 50 lbs 30 g
5 Check (H20)

 

Bioassay 3: Slide dip exposure

This bioassay used a slide dip exposure method to test the toxicity of Cinnerate at two rates, and Surround CF. Cinnerate was tested at experimental rates, higher than what is listed on the label. Consult the label for current field rates.

Methods

This bioassay followed the same methods explained in bioassay 1, only with different insecticide treatments (see Bioassay 3 Treatment List).

Results

Cinnerate was highly toxic to adult psylla for both rates at 72 hours after exposure; however, the higher rate achieved the greatest mortality (100%). The higher rate also acted more quickly, achieving 90% mortality by 48 hours.

*Surround side note: Surround is most well known for its ability to repel psylla from trees by masking host plant and them less “pleasant” to touch. Some readers may wonder why we tested Surround for acute toxicity of pear psylla in these bioassays. Past work has demonstrated that Surround significantly reduces psylla survival at various life stages (Puterka et al. 2005). When sprayed directly on psylla it impairs their ability to hold onto host plants, eventually resulting in death. We wanted to know if Surround alone could kill pear psylla, out-right. These bioassays suggest that Surround CF is not directly toxic to pear psylla; however, in a field setting Surround may prevent psylla from reaching their host and laying eggs, which is functionally the same as killing them. This presents and important point, that acute mortality is not the only way measure management potential.

Bioassay 3: Treatment List

Trt. Product Rate/100 gallons Amt./ 500ml
1 Cinnerate 60 fl oz 2.35 ml
2 Cinnerate 40 fl oz 1.56 ml
3 Surround CF 50 lbs 30 g
4 Check (H20)

 

References Cited

 Puterka, G. J., D. M. Glenn, and R. C. Pluta. 2005. Action of particle films on the biology and behavior of pear psylla (Homoptera: Psyllidae). J. Econ. Entomol. 98: 2079.

SAS. 2017. Statistical Analysis Institute. SAS/Stat User’s Guide, Release v 9.4 Edition.  SAS Institute, Inc., Cary, NC.

Contacts

Elizabeth BeersElizabeth Beers

Department of Entomology
Washington State University
Tree Fruit Research & Extension Center
Wenatchee, WA 98801Phone: 509.663.8181 x234
email: ebeers@wsu.edu

Louis Nottingham, PhD

Postdoctoral Research Associate
Washington State University
Tree Fruit Research & Extension Center
1100 N Western Ave., Wenatchee, WA 98801
louis.nottingham@wsu.edu

Disclaimer: Some of the pesticides discussed in this presentation were tested under an experimental use permit granted by WSDA. Application of a pesticide to a crop or site that is not on the label is a violation of pesticide law and may subject the applicator to civil penalties up to $7,500. In addition, such an application may also result in illegal residues that could subject the crop to seizure or embargo action by WSDA and/or the U.S. Food and Drug Administration. It is your responsibility to check the label before using the product to ensure lawful use and obtain all necessary permits in advance.

Use pesticides with care. Apply them only to 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. The information in this correspondence is not meant to endorse the use of any product.

 

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