Dicamba drift alters plant-herbivore interactions at the agro-ecological interface

Natural populations evolve in response to biotic and abiotic changes in their environment, which shape species interactions and ecosystem dynamics. Agricultural systems can introduce novel conditions via herbicide exposure to non-crop habitats in surrounding fields. While herbicide drift is known to produce a variety of toxic effects in plants, little is known about its impact on non-target wildlife species interactions. In a two-year study, we investigated the impact of herbicide drift on plant-herbivore interactions with common weed velvetleaf (Abutlion theophrasti) as the focal species. The findings reveal a significant increase in the phloem feeding silverleaf whitefly (Bermisia tabaci) abundance on the plants exposed to herbicide at drift rates of 0.5% and 1% of the field dose. Additionally, we found evidence that drift imposes correlated selection on whitefly resistance and growth rate as well as positive linear selection on herbicide resistance. We also identified a significant phenotypic tradeoff between whitefly resistance and herbicide resistance in addition to whitefly resistance and relative growth rate in the presence of dicamba drift. These findings suggest herbicide exposure to non-target communities can significantly alter herbivore populations, potentially impacting biodiversity and community dynamics of weed populations found at the agro-ecological interface.

Detection of Target-Site Herbicide Resistance in the Common Ragweed: Nucleotide Polymorphism Genotyping by Targeted Amplicon Sequencing

Background: The spread of herbicide-resistance Ambrosia artemisiifolia threatens not only the production of agricultural crops, but also the composition of weed communities. The reduction of their spread would positively affect the biodiversity and beneficial weed communities in the arable habitats. Detection of resistant populations would help to reduce herbicide exposure which may contribute to the development of sustainable agroecosystems. Methods: This study focuses on the application of target-site resistance (TSR) diagnostic of A. artemisiifolia caused by different herbicides. We used targeted amplicon sequencing (TAS) on Illumina Miseq platform to detect amino acid changes in herbicide target enzymes of resistant and wild-type plants. Results: 16 mutation points of four enzymes targeted by four herbicide groups, such as Photosystem II (PSII), Acetohydroxyacid synthase (AHAS), 5-enolpyruvylshikimate 3-phosphate synthase (EPSPS) and protoporphyrinogen IX oxidase (PPO) inhibitors have been identified in common ragweed populations, so far. All the 16 mutation points were analyzed and identified. Out of these, two mutations were detected in resistant biotypes. Conclusions: The applied next-generation sequencing-targeted amplicon sequencing (NGS-TAS) method on A. artemisiifolia resistant and wild-type populations enable TSR detection of large sample numbers in a single reaction. The NGS-TAS provides information about the evolved herbicide resistance that supports the integrated weed control through the reduction of herbicide exposure which may preserve ecological properties in agroecosystems.

Controlled-release Formulations of Trifluralin Herbicide by Interfacial Polymerization as a Tool for Environmental Hazards

Trifluralin is a widely used herbicide that can be an environmental hazard due to its sensitivity to photodegradation and volatilization to the atmosphere. Using modern techniques, such as microencapsulation, may help maintain trifluralin activity for an appropriate period and reduce applications' quantity and frequency. This work aimed to develop controlled-release formulations of trifluralin by microencapsulation of the active ingredient using interfacial polymerization. The successful encapsulation of trifluralin in the polyurethane network was confirmed by IR and 1HNMR spectroscopy, showing the two compounds' corresponding signals. Dissipation of trifluralin in the microencapsulation and EC formulations were tested with the herbicide exposure to UV light in a reactor for 0, 2, 4, 6, and 8 h. The results showed that the formulation significantly affected herbicide dissipation (P≤0.01). With increasing UV exposure, the active ingredient in the EC formulation decreased linearly and reached 43% after 8 h. In comparison, only 0.9% of the initial herbicide level in the microencapsulation was lost during the same time. Our results indicated that an effective herbicide such as trifluralin can be protected from volatilization and photodegradation by developing a microencapsulation formulation.