Organic growers face multiple insect control problems, with few organically registered effective insecticides compared to conventional growers. This project develops and tests treatments to simultaneously manage Colorado potato beetle and potato leafhopper, two pests that are challending for different reasons. Potato beetles rapidly evolve resistance and some populations are resistant to most organic and conventional insecticides. Potato leafhopper is a long distance migrant unaffected by cultural controls such as crop rotation, and a significant source of reduced yield in organic cropping systems. We are testing plant-based synergists, primarily dillapiole, to enhance pyrethrum, early season use of copper fungicide to limit leafhopper populations, and azadiractin to control leafhoppers and manage resistance in 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 against potato beetles but prone to resistance evolution, and at the same time limit potato leafhopper populations.
Objective I, Test the effectiveness of dillapiole in reducing the LD50 of both potato beetles and potato leafhoppers in laboratory leaf-dip assays.
Objective II, 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 will 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.
Dillapiole was tested in both leaf-dip and direct-application assays against potato beetles and consistently reduced the LD50 by around 50%. For example in figure 1, the LD50 to pyrethrumwas reduced from 110 ppm to 47 ppm in beetles from an organic farm in Suffolk co. NY. A farm in Ovid NY had potato beetles that are more tolerant of pyrethrum but also had its LD50 halved using dillapiole. We were not able to collect enough leafhoppers for leaf-dip bioassay, so we will start colonies earlier in the spring to produce nymphs for trials.Figure 1 synergist trial
In 2016 our own plots did not survive the drought to use for testing field applications of pyrethrum with and without synergist, but we worked with a farm in Ovid NY to trial pyrethrum with and without dillapiole synergist. We treated about 120 meters (2 rows each) of two varieties (red norland and Kennebec) with label rate Pyganic™ and Pyganic™ plus dillapiole twice in July. Both formulations of pyganic eliminated leafhoppers temporarily. There was no significant effect of treatments on potato beetle larval density, though the trend was as predicted (1.5 larvae per stalk in control potato, 1.1 larvae per stalk in pyrethrum alone, and 0.5 larvae per stalk in pyrethrum plus synergist.
In 2017 we worked with two farms; an organic farm (Plowbreak farm owned by Kara Cosulito and Aaron Munzer in Hector NY) and a conventionally managed farm (Silver Queen, owned by Gordon Gallup in Trumansburg NY). Though not organically managed, Gordon does not use systemic insecticides at planting and left the research rows untreated for insects during our study. We applied label rate of Pyganic™ and Pyganic™ plus dill-seed oil (estimated 4:1 dillapiole:pyrethrum) 5 times from June 19th through July 22nd at Plowbreak farm, and 4 times from June 29th through July 22nd at Silver Queen. Approximately 20 stalks were sampled in each treatment immediately before and 1-2 days after each treatment. There were no significant numbers of potato beetles observed at Silver Queen farm in any treatments, and there were no differences in (low to moderate) beetle densities at Plowbreak, though adult beetles peaked at 0.33 per stalk on control plants vs 0.1 and 0.05 per stalk on treated plans (ns). Both formulations of pyganic reduced leafhopper nymph and adult numbers at both farms, and suppressed total leafhopper population pressure (Figures 2,3). Adult leafhopper peaked at over three per stalk both farms, but remained at near 1/stalk using pyganic with or without dillapiole synergist. There was no significant effect of treatments on potato beetle larval density, though the trend was as predicted (1.5 larvae per stalk in control potato, 1.1 larvae per stalk in pyrethrum alone, and 0.5 larvae per stalk in pyrethrum plus synergist.
10 plants per treatment were excavated on each farm and potato weighed. There were no differences in yield between pyganic with or without dill. When those are pooled, the yield of all treated potato was not significantly different from untreated controls, though the P-value was marginal (P54,1=0.065) and the yield in treated plants was 25% higher than untreated. I suspect if we’d weighed more than ten plants per treatment the difference in yield would have been statistically significant. Both growers cooperating are willing to extend the experiment
We demonstrated a synergist effect of dillapiole, more reliably than with dill seed oil. So far trials have all use 4:1 synergist:pyrethrum ratio. This spring we will test varying synergist ratios, alternative treatments (spinosad and azadiractin), dillapiole vs piperonyl butoxide, and persistence in light and darkness. This summer we will run trials at three organic farms (we added a third collaborating farm after the grant was funded) of pyrethrum with and without dill to manage both potato beetles and leafhoppers. We had a late start last spring working with farms, and treatments started only in early July. This year we will start our own scouting earlier, and will start treatments in June, when either leafhopper nymphs exceed 0.25/leaf or first generation potato beetle egg masses have hatched. The main challenges for this season are culturing potato leafhoppers for trials, and experimenting with lower application rates to see whether the synergist can lower effective application rates, particularly for leafhoppers.
Education & Outreach Activities and Participation Summary
This project was a central part of the investigative lab component for two summer courses, Biology 386 Agro-ecology and Biology 321 Entomology at Queens College CUNY. 13 and 15 students from Queens NY spent a month (July) in Ithaca NY in 2016 and 2017. As part of the classes they received a general introduction to organic farming and the challenges and possibilities for young farmers through a guided farm visit at Plowbreak farm, presented by both Kara Cosulito and Aaron Munzer. After the initial farm visit the students learned insect identification, scouting techniques, and bioassay using the treatment plots and other crops on the co-operating farms. This project was also used to train one Masters student and 3 undergraduate assistants.
leafhopper phenology and impact
The ultimate impact of this project is to reduce the number of spinosad applications and increase the leafhopper control in organic potato farms. With the completion of the second season we will present our results at regional and national entomology meetings, and intend to present at local grower (Long Island Ag forum, NOFA-NY) meetings as well. Neither cooperating farm used spinosad in the second season, and this project demonstrated good leafhopper control using pyganic with or without synergist.
What was missing in the first two seasons was good scouting of natural enemies / beneficials. There is great variability among seasons, drought in year one, very wet soil suppressing germination in the second year, and variable insect pressure, revealing that multiple years are needed to test efficacy against multiple pests. While dillapiole and dill-seed oil extract lower resistance of beetles in the lab, we will need one more field season with greater beetle pressure to see if it has any effect in the field. We confirmed earlier research showing that pyganic can suppress leafhopper populations, but the frequent treatments we used highlights the importance of scouting for natural enemies and effects of frequent spraying on natural enemies, which we will do in the third season. There is a need in the Northeast for organic or minimal-insecticide (anyone not using in-furrow systemic neonicotinoids) to recognize and manage leafhoppers to maximize yield.