There is a compelling need across several industries to substitute non‐degradable, intentionally added microplastics with biodegradable alternatives. Nonetheless, stringent performance criteria in actives’ controlled release and manufacturing at scale of emerging materials hinder the replacement of polymers used for microplastics fabrication with circular ones. Here, the authors demonstrate that active microencapsulation in a structural protein such as silk fibroin can be achieved by modulating protein protonation and chain relaxation at the point of material assembly. Silk fibroin micelles’ size is tuned from several to hundreds of nanometers, enabling the manufacturing—by retrofitting spray drying and spray freeze drying techniques—of microcapsules with tunable morphology and structure, that is, hollow‐spongy, hollow‐smooth, hollow crumpled matrices, and hollow crumpled multi‐domain. Microcapsules degradation kinetics and sustained release of soluble and insoluble payloads typically used in cosmetic and agriculture applications are controlled by modulating fibroin's beta‐sheet content from 20% to near 40%. Ultraviolet‐visible studies indicate that burst release of a commonly used herbicide (i.e., saflufenacil) significantly decreases from 25% to 0.8% via silk fibroin microencapsulation. As a proof‐of‐concept for agrochemicals applications, a 6‐day greenhouse trial demonstrates that saflufenacil delivered on corn plants via silk microcapsules reduces crop injury when compared to the non‐encapsulated version.
Protoporphyrinogen oxidase (PPO) inhibiting herbicides remain an important and useful chemistry 60 years after their first introduction. In this review, based on topics introduced at the WSSA 2021 symposium titled “A History, Overview, and Plan of Action on PPO Inhibiting Herbicides”, we discuss the current state of PPO inhibiting herbicides. Renewed interest in the PPO inhibiting herbicides in recent years, due to increased use and increased resistance cases, has led to refinements in knowledge regarding the mechanism of action of PPO inhibitors. Herein we discuss the importance of the two isoforms of PPO in plants, compile a current knowledge of target site resistance mechanisms, discuss non target site resistance cases and review crop selectivity mechanisms. To effectively study and compare PPO inhibitor resistance cases, consistent and reproducible greenhouse screening and target site mutation assays are necessary. To this end we cover best practices in screening to accurately identify resistance ratios and properly interpret common screens for point mutations. The future of effective and sustainable PPO inhibitor use relies on development of new chemistries that maintain activity on resistant biotypes and the promotion of responsible stewardship of PPO inhibitors both new and old. We present the biorational design of the new PPO inhibitor trifludimoxazin to highlight the future of PPO inhibitor development and discuss the elements of sustainable weed control programs using PPO inhibitors as well as how responsible stewardship can be incentivized. The sustained use of PPO inhibitors in future agriculture relies on the effective and timely communication from mode of action and resistance research to agronomists, extension workers, and farmers themselves.
In Arkansas, resistance to protoporphyrinogen IX oxidase (PPO)-inhibiting herbicides in Amaranthus palmeri S. Wats. is mainly due to target site mutations. Although A. palmeri PPO-mutations are well investigated, the cross-resistance that each ppo mutant endows to weed populations is not yet well understood. We aimed to evaluate the response of PPO-resistant A. palmeri accessions, harboring the ppo2 mutations ΔG210 and G399A, to multiple PPO-inhibiting herbicides. Six resistant and one susceptible field accessions were subjected to a dose–response assay with fomesafen, and selected survivors from different fomesafen doses were genotyped to characterize the mutation profile. The level of resistance to fomesafen was determined and a cross-resistance assay was conducted with 1 and 2 times the labeled doses of selected PPO herbicides. The accession with higher predicted dose to control 50% of the population (ED50) had a higher frequency of ΔG210-homozygous survivors. Survivors harboring both mutations, and those that were ΔG210-homozygous, incurred less injury at the highest fomesafen rate tested (1120 g ai ha−1). The populations with a high frequency of ΔG210-homozygous survivors, and those with individuals harboring ΔG210 + G399A mutations, exhibited high potential for cross-resistance to other PPO herbicides. The new PPO–herbicide chemistries (saflufenacil, trifludimoxazin) generally controlled the PPO-resistant populations.
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