Novel approaches to integrated management of potato beetle and leafhopper in organic potato

View the project report

• 2016 annual report

Commodities

• Agronomic: potatoes

Practices

• Crop Production: application rate management
• Pest Management: botanical pesticides, integrated pest management

Organic growers face multiple insect control problems, with few organically registered effective insecticides. This project develops and tests treatments to simultaneously manage resistance to insecticides in Colorado potato beetle, a pest notorious for rapidly evolving resistance, and potato leafhopper, a long distance migrant unaffected by cultural controls such as crop rotation, and a significant source of reduced yield in organic cropping systems. I will test plant-based synergists including dillapiole to enhance pyrethrum, early season use of copper fungicide to limit leafhopper populations, and azadiractin to partly control both leafhoppers and potato beetles. The goals of this project are to identify treatments that can simultaneously provide farmers with organic alternatives to spinosad, a highly effective insecticide prone to resistance evolution, and at the same time limit potato leafhopper populations, that are not affected by local cultural control, have few significant natural enemies and are expected to increase in pest severity over the medium future.

We propose to use plant-based synergists to enhance the effectiveness of pyrethrum against both potato beetles and potato leafhopper. We will also test whether an organic-approved fungicide, copper sulphate and lime, has insecticidal properties. In Objective I, we test the effectiveness of dillapiole, a component of several members of the Apiaceae family that has been reported as a pyrethrum synergist, in reducing the LD₅₀ of both potato beetles and potato leafhoppers in laboratory leaf-dipassays. We will test whether dillapiole extends the duration of toxicity of pyganic under bright-light conditions. In Objective II, we test how pyrethrum with dill-oil as a source of dillapiole compares to un-synergised pyrethrum, spinosad, versus untreated potato controls in field plots both on my own research farm in Dryden NY, and in test plots planted by cooperating growers in Ovid, NY and Eastern Long Island. On the research farm plots only we will also test Bordeaux mixture (copper sulphate and lime) applied in early June to see whether leafhopper populations are suppressed relative to control plots. In Objective III we grow dill and seed-fennel, and test whether aqueous extracts from dill leaves and seeds, and fennel root, can synergize pyrethrum in leaf dip assays.

We combine bioassay tests throughout the year on both potato beetles (CPB) and leafhoppers (plh), with field trials each of two summers on my own farm and one or two cooperating farms.

Methods

Insects and location: Bioassay trials of CPB will be carried out throughout the year using a laboratory colony of moderately resistant beetles (LC₅₀ for pyrethrum alone similar to the ‘Resistant’ line in Liu et al. 2014) established for this study from beetles collected in 2015 from the cooperating farm. These beetles are reared continuously under LD 16:8 and 25°C in three Percival incubators to maintain summer breeding condition all year. We will rear plh on fava bean as soon as they can be collected in the field, which varies from early to late June depending on the year (Maredia et al. 1998). Adult plh will be provided young plants for oviposition, creating weekly cohorts to assay one month after each is established. The summer field seasons (June-August) will mostly take place on my 13 acre farm in Ithaca NY. This farm will have one 25’*60’ cinderblock poultry barn dedicated to this project with electricity. Out of ½ acre of land cultivated for garden, teaching or research crops, 14,000 square feet will be dedicated to this project.

Bioassay: While direct application of ingredient dissolved in acetone onto the abdomens of second instar CPB is highly repeatable, leaf-dip bioassays may be more realistic, and can test for some kinds of avoidance or behavioral resistance, or absorption through the gut, and not just metabolic resistance and permeability of the integument. Leaf-dip is also the only method I can use on leafhoppers. Direct application assays will be carried out on 2^nd instar larvae with 1µl droplets of ingredient dissolved in acetone similarly to Baker et al. 2007 and 2014. Mortality is defined as failure to move for 10 seconds after being flipped. Leaf dip bioassay will be as follows. Aqueous solutions of pyrethrum will be made by dilution of Pyganic® 5.0 (MGK, Minneapolis MN) with water. Synergist will be diluted first in acetone, then in water, and used to dilute Pyganic® to a 4:1 synergist:pyrethrum ratio at 500 ppm pyrethrum, the optimal ratio in one study (Hill 2008). 2 cm diameter leaf discs will be dipped in solutions and held on wire racks to dry for 10 minutes. 5-10 2^nd instar CPB larvae, or 5 plh adults, are placed on the leaf disc resting on filter paper in a 35mm petri and held for 24 hours. All petris will be coded to conceal dosage information and scored after 24 hours.

Questions addressed using Bioassay: Because it is easier to rear CPB, for several trials a range of concentrations will be tested on CPB, and the LC₅₀ or LC₉₀ for CPB will then be used to assay plh at a single dose. First we will test a range of concentrations of pyganic with and without dillapiole and then we will test a range of synergist ratios at the LC₅₀ for un-synergized pyrethrum, to determine where the effect of synergist plateaus. We will test the persistence of pyrethrum in darkness up to 12 hours by storing leaf discs in a lightproof box, and in full sunlight by dipping marked leaves still on plants in sunlight out of doors at the LC₉₀ for un-synergized pyrethrum, and cutting leaf discs at subsequent time intervals up to 6 hours. We will compare the effectiveness of dill seed oil (Anethum sowa) from two suppliers with pure dillapiole, as dill seed oil is less expensive than dillapiole.

Field trials: I will test as wide a range of treatments as possible on my farm, and our cooperating farmer will test one treatment in 2016 and 2017. I will plant 1,600 row feet divided into 20 plots, each twenty feet by four rows. Each plot will be divided into 10’ each of a leafhopper-susceptible variety, Dark red norland, and a leafhopper tolerant variety, Elba. Each year there will be four treatments plus control, giving four plots to each. In 2016 the treatments will be Control, Pyrethrum alone, Pyrethrum with dill, early season Bordeaux mixture (copper sulphate and hydrated lime), and Azadirachtin. I will also plant a small number of plants to be sprayed with label rates of spinosad, or treated in-furrow with imidacloprid, to harvest treated leaf discs for bioassay comparisons. A collaborating farm will plant about twenty 500’ rows in a variety of potato. In 2016 after a first spray with spinosad, I will scout for emergence of summer adults and we will time the second spray to target the second generation CPB larvae. We will divide his field into four sections and, depending on the insect pressure, we will either spray two quarters with spinosad, and two with Pyganic® plus dillapiole synergist, or we will leave two quarters unsprayed, and spray two quarters with Pyganic® plus dillapiole. In the second season I will change my treatments to combine two of the most effective treatments from the first season; Pyganic® plus synergist, azadiractin, or Bordeaux. We will examine the results from all trials and determine the treatments for 2017.

Expected results: Preliminary trials indicate dillapiole halves the LC₅₀ of pyrethrum. I will replicate and test for any similar effect found with plh. Dillapiole might be more effective with CPB, where PBO is known to increase pyrethroid mortality in both high- and low-resistance populations (Zamojska et al. 2011). I expect pyrethrum to have good persistence in darkness, and less of an effect of synergist. I expect an effect of synergist in sunlight, if present, to be at the shortest time intervals, ½ or 1 hour. I expect the dill seed oil to function similarly to dillapiole at similar concentrations. Finally, I am very interested in bringing leaf discs from field trials in to the lab for bioassay. While there is a good qualitative match between bioassay results and farmer characterization of resistance (Alyokhin et al. 2007), this will offer a new opportunity to validate bioassay results with field application rates.

Assays using potato beetle (CPB) will start in 2016 using an existing laboratory colony and continue with field caught beetles. Leafhopper assays will begin in summer 2016 using field caught adults and nymphs to establish colonies, and continue into the fall and winter. Field trials for single-treatments will take place on my farm in 2016 and for Pyganic® plus dillapiole on the collaborating farm in 2016, and for interactions on my farm in 2017 and one refined treatment on the collaborating farms in 2017. While I will learn a great deal about synergists in the first year, a two-year project is especially valuable to increase the likelihood of encountering a heavy leafhopper season. Leafhopper timing of migration and infestation severity varies widely each year. While potato beetles are less variable, and in a pinch I might even seed my own plots with equal numbers of CPB if necessary, plh levels vary widely enough that heavy yield loss in controls, and an opportunity to observe successful management, does not happen every year.

Outreach plan

We will publicize our results through traditional agricultural outlets. We will present our results in the Organic Vegetable Field Day at the Homer Thompson Research Farm in Freeville, NY, and the Long Island Agriculture Forum sponsored by CCE Suffolk, and the NOFA Winter Conference, where I presented in 2014. While we will no doubt meet some ag professionals at the LI Ag forum and NOFA meetings, we will also present our work at the Entomological Society of America’s annual and Eastern Branch meetings, and publish our results in journals such as Environmental Entomology.

I will also teach a three week agro-ecology field course based on my farm in Ithaca NY during the summers of 2016-17. I have taught a field agro-ecology or entomology course on my farm each of the last four summers. The research students partly supported by this grant will participate in the course as students and leaders. This research project will be incorporated into the course in diverse ways. For example, while carrying out a general soil lab looking at organic matter and nutrient content, we will also analyze soil samples for Beauveria, comparing the early Bordeaux mixture vs other plots from our project and farms that use chemical pesticides including fungicides. The pulse of student labor power will also allow short, intense surveys of different guilds of natural enemies in plots with different treatments. Undergraduates from New York City are a valuable target for changing peoples food choices and attracting students to the field that might not have considered agro-ecology or sustainable agriculture.

References

Alyokhin, A., M. Baker, D. Mota-Sanchez, G. Dively, and E. Grafius. 2008. Colorado Potato Beetle Resistance to Insecticides. American Journal of Potato Research 85: 395-413.

Alyokhin, A., G. Dively, M. Patterson, C. Castaldo, D. Rogers, M. Mahoney, and J. Wollam. 2007. Resistance and cross-resistance to imidacloprid and thiamethoxam in the Colorado potato beetle Leptinotarsa decemlineata. Pest Management Science 63: 32-41.

Angioni, A., F. Dedola, E. V. Minelli, A. Barra, P. Cabras, and P. Caboni. 2005. Residues and half-life times of Pyrethrins on peaches after field treatments. Journal of Agricultural and Food Chemistry 53: 4059-4063.

Baker, M., K. Hossain, K. Zabierek, K. Collie, A. Alyokhin, D. Mota-Sanchez, and M. Whalon. 2014. Geographic Variation in Cannibalism in Colorado Potato Beetle (Coleoptera: Chrysomelidae) Populations. Environmental Entomology 43: 102-109.

Baker, M. B., P. D. Venugopal, and W. O. Lamp. 2015. Climate Change and Phenology: Empoasca fabae (Hemiptera: Cicadellidae) Migration and Severity of Impact. Plos One 10.

Liu, S. Q., I. M. Scott, Y. Pelletier, K. Kramp, T. Durst, S. R. Sims, and J. T. Arnason. 2014. Dillapiol: A Pyrethrum Synergist for Control of the Colorado Potato Beetle. Journal of Economic Entomology 107: 797-805.

Maredia, K. M., M. E. Whalon, S. H. Gage, and M. J. Kaeb. 1998. Observations of first occurrence and severity of potato leafhopper, Empoasca fabae (Harris), (Homoptera : Cicadellidae) in the north central and eastern United States. Great Lakes Entomologist 31: 73-84.

Zamojska, J., Węgorek, P., and M. Mrówczyński. 2011. Changes in the colorado potato beetle (leptinotarsa decemlineata say) susceptibility level to pyrethroids and the pest resistance mechanisms to deltamethrin. Journal Of Plant Protection Research 51(3) 294-99.