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X-disease phytoplasma vector management for 2020

By Tianna DuPont, WSU Extension; Tobin Northfield, WSU Entomology. July 7, 2020. Update Aug 20, 2020.

Managing the leafhopper vectors of X-disease phytoplasma post-harvest is important this season to slow the spread of the pathogen. Here we cover basic considerations. Keep in mind there are many unknowns about these leafhoppers and management options will be refined as new research is completed.

Which leafhoppers should I worry about?

Six leafhoppers are known to transmit X-disease phytoplasma: Colladonus montanus, Fiebriella florii, Scaphytopius acutus, Paraphlepsius irroratus, Colladonus reductus, and Colladonus geminatus. The three  most common in Washington are C. reductus, C. geminatus and to a lesser extent C. montanus.

How do I ID the problem leafhoppers?

The leafhoppers which vector X-disease phytoplasma can be tricky to distinguish from the many other leafhoppers hopping around your orchard. There are approximately 20,000 leafhopper species, so it is important to focus on the correct ones. When you trap them on a sticky card for monitoring look for what appears to be a face with a handlebar mustache, a pirate hat and sunglasses on the back of the C. geminatus. and C. reductus has a bright yellow stripe on its back.

Fig 1. C. geminatus left and C. reductus right. Look for the face of a pirate with sunglasses and a handlebar mustache on the back of the C. geminatus. Look for a distinct yellow stripe on the C. reductus. The rarely seen vector C. montanus looks nearly identical to C. reductus, but also has a small yellow patch on the back. Photo credit T. Northfield, WSU Entomology.

 

 Trapping basics

Figure 2 Yellow sticky card trap 3-5 ft up in canopy.
  • Use yellow sticky cards.
  • Deploy post-harvest.
  • Hang at 3-5 feet from the orchard floor.
  • Place traps on orchard borders, in areas of concern in your block and throughout block. Approx. 1 trap per two acres.
  • Check traps every 1-2 weeks.
  • Use presence (an average of 1 leafhopper per trap) as a threshold to spray.[i]

[i] An economic threshold for leafhopper vectors of X-disease phytoplasma has not been established. Generally, for disease vectors presence is considered an action threshold. although it depends on the level of local disease pressure. Once an epidemic has subsided and disease levels are reduced the action threshold may be higher.

Horticulture suggestions

  • Be aware that mowing will likely incite movement of leafhoppers, due to their use of weedy hosts in the groundcover.
  • Grass in drive rows will help out-compete broadleaf weeds which can be an alternative host for the pathogen—grasses do not host phytoplasmas.
  • Broadleaf herbicides will reduce alternative hosts.

Pesticide applications

Manage leafhoppers when they are present – generally after harvest through October based on sticky card trap monitoring. If leafhoppers are present (avg. 1 or more per trap) spray rotating between pesticide groups. With the residual of common (conventional) products sticky cards will likely show 21-30 days of control necessitating 4 to 6 after harvest sprays per season.

For example, rotating between:

  • group 3 pyrethroid (e.g. Warrior)
  • group 4 neonicotinoid (e.g. Actara)
  • a new active group (e.g. Bexar group 21A)
  • back to a group 3 or group 4
  • group 1 (e.g. Carbaryl) late in season when leaf-drop is not a concern.

Remember it takes several weeks after feeding on an infected tree for a leafhopper to be able to transmit the phytoplasma. The phytoplasma has to pass through the insect gut into the ‘blood’ to the salivary glands. Every two to three weeks sprays should be the shortest interval needed. More frequent sprays will mean you likely run out of legal applications before the end of the season when transmission is likely to be highest.

Washington product trials have mostly been tested on white apple leafhopper and the California trials centered on their common leafhoppers C. montanus and F. florii. Work with Washington common leafhoppers C. reductus and C. geminatus is ongoing and will be used to refine recommendations.

Kaolin clay (eg Surround) may be a good option in orchards where limited sprays are possible. Kaolin confuses insects reducing feeding and generally has long residue (approx 4 weeks). Unlike broad spectrum options below few indirect effects on natural enemies should reduce the possibility of mite flare ups. This product is currently being tested by the Northfield lab.

Table 1. Example Products Labeled for Leafhoppers in Cherry in WA*

Excellent (E) 80-90% control; Good (G) 50-79% control; Moderate (M) 30-49% control; Poor (P) <30% control; Not rated (NR).

Group Active Product Rate per A** Efficacy Notes
3A1 Lambda-cyhalothrin 22.8% Warrior II 2.5 fl oz NR 95% control potato leafhoppers [1]. For potato leafhoppers Warrior II CS at 1.9 fl oz had number 40% lower than untreated control (not sig.) [2].
3A Esfenvalerate Asana XL 2-5 fl oz E Asana had 80-90% control in 8 CA trials and 50-79% in 1 CA trial [3-7].
3 Fenpropathrin 30.9% Danitol 18 fl oz G-E It is generally recommended that no more than 2 Danitol 2.4 EC apps per season. Danitol had 68-94% control in four California trials at 0.2 and 0.4 lb AI/a [8].
4A2 Imidacloprid   3.2 fl oz P-E Provado rated as high efficacy on White apple leafhopper in WA trials [9]. Provado provided 8%, 20%, 34%, 69%, 30%, 34%, 51% and 73% control in eight California trials [3,6,10]. Many generics now available. E.g. Macho, Asada, Midash Forte.
4A Thiamethoxam Actara 2.5 oz G-E Actara had more than 80% control in 10 CA trials, above 50% in 2 CA trials and 30-50% in 1 CA trial [3-7] Generally thought to be good on nymphs and poor on adults.
4A Acetamiprid 70% Assail WP 1.7 oz P-G Assail had 20, 25, 40 and 52% control in four California trials [6]. Generally higher efficacy on younger instar nymphs.
21A3 Tolfenpyrad Bexar 21 fl oz NR
1 Carbaryl Sevin SL 2-3 qt G-E Can cause leaf-drop in Canadian varieties. Use fall only. Sevin had 50-90% in 5 CA. [4].
6 Abamectin Agri-mek M-E Generally thought to be good on nymphs and poor on adults. Rated excellent control White apple leafhopper nymphs West Virginia [11]. 50% control nymphs and adults New York [12].
22A Indoxacarb Avaunt 30DG 6 oz G-E Rated good to high efficacy on White apple leafhopper in WA [9].
5 Spinosad Success 2-2.7 fl oz G Rated as good efficacy on White apple leafhopper in WA [9].
*Products with a cherry label and Washington leafhopper data also included.
**Assumes 100 gal/A. See label for higher gallonage applications.
1Pyrethroid: Sodium channel modulators. Keeps sodium channels open causing hyperexcitation and sometimes nerve block. Pyrethroids applied at this time can be disruptive to beneficials. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
2Neonicotinoids Nicotinic acetylcholine receptor (nAChR) competitive modulators. Bind to the acetylcholine site on nAChRs causing a range of symptoms from hyper-excitation to lethargy and paralysis.
3Meti Mitochondrial complex I electron transport inhibitors. Inhibit electron transport complex 1, preventing the utilization of energy by cells.
Table 2. Example Certified Organic Products Labeled for Leafhoppers in Cherry in Washington

Excellent (E) 80-90% control; Good (G) 50-79% control; Moderate (M) 30-49% control; Poor (P) <30% control; Not rated (NR).

Group Active Product Rate Efficacy  Notes
Azadirachtin AzaDirect 1-2 pt NR Aza-direct at 32oz provided 62%, 78% control of white apple leafhopper and 63%, 25% of potato leaf hopper in apples [13]. Azadirect 32oz provided 64% of control for potato leafhopper nymphs [14].
3A Pyrethrins/ Azadirachtin Azera NR Azera 40oz provided 64% of control for potato leafhopper nymphs [14].
3A Pyrethrin Pyganic see label NR Pyganic 17 fl oz (3 applications) provided 66% control for potato leafhopper nymphs [14].
  Azadirachtin Neemix 16 oz P-G Neemix at 3.5 and 7 fl oz provided little control compared to the check (Sevin) for white apple leafhoppers for first or second generations [15, 16]. Neemix 4.5 at 8 oz provided 67% control potato leafhopper adults 7 days after treatment [17].
  Kaolin Surround WP 25-50 lb E Kaolin confuses insects where they don’t recognize the plants to feed. Kaolin reduced disease transmission of Pierces disease by glassy winged sharpshooters better than conventional products in one trial [18]. 100% control of white apple leafhoppers [13]. Surround + Trilogy 49% control potato leafhopper adults 7 days after treatment [17].
  Mineral oil 2 gal G Oil at 2% reduced White apple leafhopper oviposition resulting in fewer nymphs [19].
  Rosemary/ Peppermint oil Ecotec See label NR Ecotec Ag EC at 24 fl oz provided 40% control of potato leafhopper nymphs [2].

 

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.

References

  1. Laub, C.A., S. Tiwari, and R.R. Youngman, Efficacy of Foliar Insecticides Against Potato Leafhopper. Arthropod Management Tests, 2003.
  2. Kuhar, T.P., Evaluation of Insecticide Treatments for the Control of Pests of Insects in Snap Beans. Arthropod Management Tests, 2009. 34.
  3. Van Steenwyk, R.A. and C.F. Fouche, Control of Mountain Leafhopper on Cherry, 1988. Insecticide and Acaricide Tests, 1989. 14(1): p. 60-61.
  4. Van Steenwyk, R.A., C.F. Fouche, and D.M. Havens, Control of Mountain Leafhopper on Cherry, 1987. Insecticide and Acaricide Tests, 1988. 13(1): p. 55-55.
  5. Van Steenwyk, R.A., D.M. Havens, and R. Freeman, Evaluation of Trap Types for Two Vectors of Western X Disease: Colladonus montanus and Fieberiella florii (Homoptera: Cicadellidae). Journal of economic entomology, 1990. 83(6): p. 2279-2283.
  6. Van Steenwyk, R.A., R.M. Nomoto, and J.A. Grant, CONTROL OF MOUNTAIN LEAFHOPPER ON SWEET CHERRY, 2001. Arthropod Management Tests, 2002. 27(1).
  7. Van Steenwyk, R.A., S.K. Zolbrod, and R.M. Nomoto, CONTROL OF MOUNTAIN LEAFHOPPER ON SWEET CHERRY, 2002. Arthropod Management Tests, 2003. 28(1).
  8. Steenwyk, R.A.V., et al., Control of Mountain Leafhopper on Cherry, 1992. Insecticide and Acaricide Tests, 1993. 18(1): p. 65-65.
  9. DuPont, S.T., et al., Crop Protection Guide for Tree Fruits in Washington. 2020, Washington State University.
  10. Grant, J.A. and R.A. Van Steenwyk, CONTROL OF MOUNTAIN LEAFHOPPER ON SWEET CHERRY, 1999. Arthropod Management Tests, 2000. 25(1).
  11. Hogmire, H.W. and T. Winfield, Insecticide and acaracide evaluation against leafhopper and mite pests 1999. Arthropod Management Tests, 1999.
  12. Reissig, H., D.H. Dunham, and C. Smith, Apple, Tests of insecticides against White apple leafhoppers, New York. Arthropod Management Tests, 1995. 21: p. 45.
  13. Wise, J.C., K. Schoenborn, and L.J. Gut, Season Long Broad Spectrum Insect Control. Arthropod Management Tests, 2002.
  14. Harding, R.S., B.A. Nault, and A. Seaman, Potato Leafhopper Control in Snap Bean With Insecticides Allowed for Organic Production, 2019. Arthropod Management Tests, 2020. 45(1).
  15. Beers, E.H., Effect of Rate and Timing of Biorational Materials for Control of First Generation White Apple Leafhopper Nymphs. Arthropod Management Tests, 1995. 21(5).
  16. Beers, E.H., Effect of rate and timing of biorational materials for control of second generation white apple leafhopper nymphs, 1995. Arthropod Management Tests, ed. A.K. Burditt, Jr. Vol. 21. 1996: Entomological Society of America {a}, 9301 Annapolis Road, Lanham, Maryland 20706, USA. 6-7.
  17. Patton, T.W. and G.P. Dively, Control of Potato Leafhopper Using Organic and Conventional Insecticides 2002. Arthropod Management Tests, 2002.
  18. Tubajikaa, K.M., et al., The effects of kaolin, harpin, and imidacloprid on development of Pierce’s disease in grape. Crop Protection, 2007. 26: p. 92-99.
  19. Fernandez, D.E., et al., Mineral oil inhibition of white apple leafhopper (Homoptera : Cicadellidae) oviposition. Journal of Entomological Science, 2001. 36(3): p. 237-243.

Contacts

Tobin Northfield, WSU Entomology tnorthfield@wsu.edu

Tianna DuPont, WSU Extension (509) 293-8758 tianna.dupont@wsu.edu

Bernardita Sallato, WSU Extension (509) 439-8542 b.sallato@wsu.edu

Ashley Thomson, OSU Extension (541) 296-5494 Ashley.Thompson@oregonstate.edu

Karen Lewis, WSU Extension (509) 760-2263 kmlewis@wsu.edu

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