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

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

Summary

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.

Objectives/Performance Targets

Objective I, Test the effectiveness of dillapiole in reducing the LD₅₀ of both potato beetles and potato leafhoppers in laboratory 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

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.

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 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.

Accomplishments/Milestones

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.

Impacts and Contributions/Outcomes

The ultimate impact of this project is to reduce the number of spinosad applications and increase the leafhopper control in organic potato farms. We plan to achieve those impacts on our cooperating farms this season. 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. The strength of our outreach will depend on the results we see in the field in the second season. 

Collaborators:

Collaborators: