What do farmers' weed control decisions imply about glyphosate resistance? Evidence from surveys of US corn fields

Novel Candidate Genes Differentially Expressed in Glyphosate-Treated Horseweed (Conyza canadensis)

The evolution of herbicide-resistant weed species is a serious threat for weed control. Therefore, we need an improved understanding of how gene regulation confers herbicide resistance in order to slow the evolution of resistance. The present study analyzed differentially expressed genes after glyphosate treatment on a glyphosate-resistant Tennessee ecotype (TNR) of horseweed (Conyza canadensis), compared to a susceptible biotype (TNS). A read size of 100.2 M was sequenced on the Illumina platform and subjected to de novo assembly, resulting in 77,072 gene-level contigs, of which 32,493 were uniquely annotated by a BlastX alignment of protein sequence similarity. The most differentially expressed genes were enriched in the gene ontology (GO) term of the transmembrane transport protein. In addition, fifteen upregulated genes were identified in TNR after glyphosate treatment but were not detected in TNS. Ten of these upregulated genes were transmembrane transporter or kinase receptor proteins. Therefore, a combination of changes in gene expression among transmembrane receptor and kinase receptor proteins may be important for endowing non-target-site glyphosate-resistant C. canadensis.

Changes in the drought sensitivity of US maize yields

As climate change leads to increased frequency and severity of drought in many agricultural regions, a prominent adaptation goal is to reduce the drought sensitivity of crop yields. Yet many of the sources of average yield gains are more effective in good weather, leading to heightened drought sensitivity. Here we consider two empirical strategies for detecting changes in drought sensitivity and apply them to maize in the United States, a crop that has experienced myriad management changes including recent adoption of drought-tolerant varieties. We show that a strategy that utilizes weather-driven temporal variations in drought exposure is inconclusive because of the infrequent occurrence of substantial drought. In contrast, a strategy that exploits within-county spatial variability in drought exposure, driven primarily by differences in soil water storage capacity, reveals robust trends over time. Yield sensitivity to soil water storage increased by 55% on average across the US Corn Belt since 1999, with larger increases in drier states. Although yields have been increasing under all conditions, the cost of drought relative to good weather has also risen. These results highlight the difficulty of simultaneously raising average yields and lowering drought sensitivity.

How low can you go? Estimating impacts of reduced pesticide use

Recent research has suggested that a high proportion of farms can dramatically reduce pesticide applications without reducing crop yields or farm profits. Yet this research has made estimation choices that may systematically bias downwards estimates of the productivity and profitability of pesticides. Fifty years of agricultural economics research provides lessons about how to avoid pitfalls in estimating pesticide productivity. Carefully executed econometric studies have found evidence of overuse, underuse, and near-optimal use of pesticides in different cropping systems. There are now standard methods to test and correct for sources of biases (either upward or downward) in estimates of pesticide productivity. Ignoring these lessons and methods can seriously bias estimates of the potential for reducing pesticide use at little or no economic cost. © 2018 Society of Chemical Industry.