Developing agricultural pest management strategies with reduced-risks to surface water: An economic case study of California's Central Coast region.

Pesticides are critical for protecting agricultural crops, but the off-site transport of these materials via spray drift and runoff poses risks to surface waters and aquatic life. California's Central Coast region is a major agricultural hub in the United States characterized by year-round production and intensive use of pesticides and other chemical inputs. As a result, the quality of many waterbodies in the region has been degraded. A recent regulatory program enacted by the Central Coast Regional Water Quality Control Board set new pesticide limits for waterways and imposed enhanced enforcement mechanisms to help ensure that water quality targets are met by specific dates. This regulatory program, however, does not mandate specific changes to pest management programs. In this study, we evaluate the economic, environmental, and pest management impacts of adopting two alternative pest management programs with reduced risks to surface water: 1) replacing currently used insecticide active ingredients (AIs) that pose the greatest risk to surface water with lower-risk alternatives and 2) converting conventional arthropod pest management programs to organic ones. We utilize pesticide use and toxicity data from California's Department of Pesticide Regulation to develop our baseline and two alternative scenarios. We focus on three crop groups (cole crops, lettuce and strawberry) due to their economic importance to the Central Coast and use of high-risk AIs. For Scenario 1, we estimate that implementing the alternative program in the years 2017-2019 would have reduced annual net returns on average by $90.26 - $190.54/ha, depending on the crop. Increased material costs accounted for the greatest share of this effect (71.9%-95.6%). In contrast, Scenario 2 would have reduced annual net returns on average by $5,628.12 - $18,708.28/ha during the study period, with yield loss accounting for the greatest share (92.8-97.9%). Both alternative programs would have reduced the associated toxic units by at least 98.1% compared to the baseline scenario. Our analysis provides important guidance for policymakers and agricultural producers looking to achieve environmental protection goals while minimizing economic impacts.

Balancing Bees and Pest Management: Projected Costs of Proposed Bee-Protective Neonicotinoid Regulation in California.

Neonicotinoid insecticides are widely used in agriculture, including in many California specialty crops. With mounting evidence that these insecticides are harmful to bees, state and national governments have increasingly regulated their use. The European Union, Canada, and United States have imposed use restrictions on several neonicotinoids, such as on the timing of applications. In 2020, California proposed a draft regulation to mitigate harm to managed pollinators from four nitroguanidine-substituted neonicotinoids (NGNs): clothianidin, dinotefuran, imidacloprid, and thiamethoxam. We use data on California pesticide use from 2015 to 2017 to analyze the economic and pest management implications of the 2020 draft proposed regulation for seven crops: almond, cherry, citrus, cotton, grape, strawberry, and tomato. From 2015 to 2017, these crops accounted for approximately 85% of total hectares treated with NGNs and 87% of NGN use by kilograms of active ingredient applied in treatments that would have been affected by the proposed regulation. These insecticides often primarily target Hemipteran insect pests. In most cases there are alternatives; however, these are often more expensive per hectare and do not have the same residual effectiveness as the NGNs, which are systemic insecticides. Overall, we estimate that pest management costs for these crops would have increased an estimated $13.6 million in 2015, $12.8 million in 2016, and $11.1 million in 2017 if the 2020 draft proposed regulation had been in effect, representing a 61% to 72% increase in the cost of managing the target pests.

Spray drift mitigation using opposing synchronized air-blast sprayers.

BACKGROUND: Pesticide drift is a serious environmental and safety concern that affects all of US agriculture. A number of mitigation techniques to reduce pesticide drift have been recommended by industry, academic and government agencies. These techniques are very costly or reduce the efficacy of the pest control product and have not been implemented by US agriculture. RESULTS: When using a novel spray technique (Air-in), pesticide drift was significantly reduced by between 53% and 99% at 7.6 m from the orchard drip line when compared to the grower standard. This technique not only reduced pesticide drift, but also maintained or improved the amount of pesticide residue deposited (by 0.7-2.6-fold) and the percentage pesticide coverage (by 1.0-1.4-fold) with different air-blast speed sprayers on almond, walnut and pistachio. CONCLUSION: The Air-in technique shows great promise in reducing pesticide drift while maintaining or improving pesticide coverage with minimal cost to the grower.

Nitrogen-Mediated Interaction: A Walnut-Aphid-Parasitoid System.

The effects of plant quality on natural enemies are often overlooked in planning and executing biological control programs for insect pests in agriculture. Plant quality, however, could help to explain some of the observed variation in effectiveness of biological control, as it can indirectly influence natural enemy populations. In this study, we used the walnut aphid Chromaphis juglandicola (Kaltenbach) to address the effect of increased nitrogen availability to the host plant on parasitism by the specialist parasitoid Trioxys pallidus (Haliday). In laboratory experiments with walnut seedlings, a higher chlorophyll content index of the foliage in response to added nitrogen was correlated with a decrease in the number of mummies produced by female parasitoids over a 24-h period but an increase in the proportion and the size of female offspring. In field sampling of walnut orchards, there was no relationship between the percent parasitism of walnut aphids by T. pallidus and the chlorophyll content index of the trees. Nitrogen fertilizer and plant quality can clearly affect biological control and should be given greater consideration in integrated pest management.

Diversification practices reduce organic to conventional yield gap.

Agriculture today places great strains on biodiversity, soils, water and the atmosphere, and these strains will be exacerbated if current trends in population growth, meat and energy consumption, and food waste continue. Thus, farming systems that are both highly productive and minimize environmental harms are critically needed. How organic agriculture may contribute to world food production has been subject to vigorous debate over the past decade. Here, we revisit this topic comparing organic and conventional yields with a new meta-dataset three times larger than previously used (115 studies containing more than 1000 observations) and a new hierarchical analytical framework that can better account for the heterogeneity and structure in the data. We find organic yields are only 19.2% (±3.7%) lower than conventional yields, a smaller yield gap than previous estimates. More importantly, we find entirely different effects of crop types and management practices on the yield gap compared with previous studies. For example, we found no significant differences in yields for leguminous versus non-leguminous crops, perennials versus annuals or developed versus developing countries. Instead, we found the novel result that two agricultural diversification practices, multi-cropping and crop rotations, substantially reduce the yield gap (to 9 ± 4% and 8 ± 5%, respectively) when the methods were applied in only organic systems. These promising results, based on robust analysis of a larger meta-dataset, suggest that appropriate investment in agroecological research to improve organic management systems could greatly reduce or eliminate the yield gap for some crops or regions.

Self-medication as adaptive plasticity: increased ingestion of plant toxins by parasitized caterpillars.

Self-medication is a specific therapeutic behavioral change in response to disease or parasitism. The empirical literature on self-medication has so far focused entirely on identifying cases of self-medication in which particular behaviors are linked to therapeutic outcomes. In this study, we frame self-medication in the broader realm of adaptive plasticity, which provides several testable predictions for verifying self-medication and advancing its conceptual significance. First, self-medication behavior should improve the fitness of animals infected by parasites or pathogens. Second, self-medication behavior in the absence of infection should decrease fitness. Third, infection should induce self-medication behavior. The few rigorous studies of self-medication in non-human animals have not used this theoretical framework and thus have not tested fitness costs of self-medication in the absence of disease or parasitism. Here we use manipulative experiments to test these predictions with the foraging behavior of woolly bear caterpillars (Grammia incorrupta; Lepidoptera: Arctiidae) in response to their lethal endoparasites (tachinid flies). Our experiments show that the ingestion of plant toxins called pyrrolizidine alkaloids improves the survival of parasitized caterpillars by conferring resistance against tachinid flies. Consistent with theoretical prediction, excessive ingestion of these toxins reduces the survival of unparasitized caterpillars. Parasitized caterpillars are more likely than unparasitized caterpillars to specifically ingest large amounts of pyrrolizidine alkaloids. This case challenges the conventional view that self-medication behavior is restricted to animals with advanced cognitive abilities, such as primates, and empowers the science of self-medication by placing it in the domain of adaptive plasticity theory.