Modeling the sustainability and economics of stacked herbicide-tolerant traits and early weed management strategy for waterhemp (Amaranthus tuberculatus) control

Diversity is key for sustainable weed management and can be achieved via both chemical and nonchemical control tactics. Genetically modified crops with two-way or three-way stacked herbicide-tolerant traits allow use of herbicide mixtures that would otherwise be phytotoxic to the crop. Early weed management(EWM)strategies promote the use of PRE herbicides with residual activity to keep the field free of weeds early in the season for successful crop establishment. To evaluate the respective sustainability and practicality of the two chemical-based management tactics(i.e.,stacked traits and EWM),we used a population model of waterhemp, Amaranthus tuberculatus (Moq.) Sauer (syn. rudis), to simulate the evolution of resistance in this key weed species in midwestern U.S.soybean [Glycinemax(L.)Merr.] agroecosystems. The model tested scenarios with a varying number of herbicide sites of action (SOAs), application timings (PRE and POST), and preexisting levels of resistance. Results showed that both tactics provided opportunity for controlling resistant A.tuberculatus populations. In general,each pass over the field should include at least two effective herbicide SOAs. Nevertheless, the potential evolution of cross-resistance may void the weed control programs embraced by stacked traits and diverse herbicide SOAs. Economic calculations suggested that the diversified programs could double long-term profitability when compared to the conventional system, because of improved yield and grain quality. Ultimately, the essence of a sustainable herbicide resistance management strategy is to be proactive. Although a herbicide-dominated approach to diversifying weed management has been prevalent, the increasing presence of weed populations with multiple resistance means that finding herbicides to which weed populations are still susceptible is becoming increasingly difficult, and thus the importance of reintroducing cultural and mechanical practices to support herbicides must be recognized

Molecular characterization of hairy fleabane using RAPD.

ABSTRACT With the increase of glyphosate resistance evolution in hairy fleabane, the knowledge of genetic diversity is essential to assist in the weed management. The objective was to characterize the genetic diversity of glyphosate resistant Conyza species in Rio Grande do Sul. Hairy fleabane biotype seeds were collected in fields of glyphosate-resistant soybean, generating seedlings used for extracting DNA from the leaves to perform a genetic diversity analysis, using the RAPD technique. The DNA was used in polymerase chain reaction and DNA fragments were assessed for polymorphism bands in electrophoresis. Biotypes were identified as Conyza bonariensis and microcephala varieties. In molecular analysis, among 25 primers RAPD, eight were reproducible generating polymorphisms of high intensity for the separation of biotypes. Cluster analysis revealed five groups, which had a genetic similarity of 53%. The results indicate that all known biotypes are of the same species, but exhibit different varieties. RAPD presents itself as an important tool for characterizing Conyza species