Crop Science

Aristilde et. al, 2017

Ludmilla Aristilde, Michael L. Reed, Rebecca A. Wilkes, Tracy Youngster, Matthew A. Kukurugya, Valerie Katz, and Clayton R. S. Sasaki, “Glyphosate-Induced Specific and Widespread Perturbations in the Metabolome of Soil Pseudomonas Species,” Frontiers in Environmental Science, 2017, 5:34, DOI: 10.3389/fenvs.2017.00034.

ABSTRACT:

Previous studies have reported adverse effects of glyphosate on crop-beneficial soil bacterial species, including several soil Pseudomonas species. Of particular interest is the elucidation of the metabolic consequences of glyphosate toxicity in these species. Here we investigated the growth and metabolic responses of soil Pseudomonas species grown on succinate, a common root exudate, and glyphosate at different concentrations. We conducted our experiments with one agricultural soil isolate, P. fluorescens RA12, and three model species, P. putida KT2440, P. putida S12, and P. protegens Pf-5. Our results demonstrated both species- and strain-dependent growth responses to glyphosate. Following exposure to a range of glyphosate concentrations (up to 5 mM), the growth rate of both P. protegens Pf-5 and P. fluorescens RA12 remained unchanged whereas the two P. putida strains exhibited from 0 to 100% growth inhibition. We employed a 13C-assisted metabolomics approach using liquid chromatography-mass spectrometry to monitor disruptions in metabolic homeostasis and fluxes. Profiling of the whole-cell metabolome captured deviations in metabolite levels involved in the tricarboxylic acid cycle, ribonucleotide biosynthesis, and protein biosynthesis. Altered metabolite levels specifically in the biosynthetic pathway of aromatic amino acids (AAs), the target of toxicity for glyphosate in plants, implied the same toxicity target in the soil bacterium. Kinetic flux experiments with 13C-labeled succinate revealed that biosynthetic fluxes of the aromatic AAs were not inhibited in P. fluorescens Pf-5 in the presence of low and high glyphosate doses but these fluxes were inhibited by up to 60% in P. putida KT2440, even at sub-lethal glyphosate exposure. Notably, the greatest inhibition was found for the aromatic AA tryptophan, an important precursor to secondary metabolites. When the growth medium was supplemented with aromatic AAs, P. putida S12 exposed to a
lethal dose of glyphosate completely recovered in terms of both growth rate and selected metabolite levels. Collectively, our findings led us to conclude that the  glyphosateinduced specific disruption of de novo biosynthesis of aromatic AAs accompanied by widespread metabolic disruptions was responsible for dose-dependent adverse effects of glyphosate on sensitive soil Pseudomonas species.  FULL TEXT

Associated Press, 2017b

Associated Press, “Farm chemical linked to oak damage,” July 2, 2017, Quad-City Times,

SUMMARY:

Reports that almost 1,000 residents of Iowa have contacted the state Department of Natural Resources about damaged leaves on oak trees (photo, right) that looked like insect damage.  Research from the University of Illinois in 2004 showed that herbicide drift was likely linked to the condition, known as leaf tatters, due to exposure to chloroacetanilide herbicides like dicamba.  Exposure occurs from direct drift but also through atmospheric volubility in areas not close to where the herbicide was applied. White oaks are particularly susceptible, and trees can die if damage to the leaves occurs over multiple years.   FULL TEXT

Barber, 2017

Tom Barber, “Dicamba Drift and Potential Effects on Soybean Yield,” AGWatch Network, July 7, 2016.

SUMMARY:

Tom Barber, an Extension Weed Scientist at the University of Arkansas, posts a chilling overview of what he has observed in soybean fields in several parts of the state. His piece “Dicamba Drift and Potential Effects on Soybean Yield” contains an ominous warning – “We have observed a 10% [soybean] yield loss from dicamba at rates as low as 1/1024X of the labeled rate” – a very low level of drift and/or movement following volatilization.  Barber also warns that low rates of dicamba drift/movement onto soybeans, especially later in the crop’s growth cycle (i.e. R3-R5) can result in carryover of dicamba in the seed…triggering problems if the soybeans are used for seed in the next year and increasing dietary exposure levels.  FULL TEXT

Begemann, 2017

Sonja Begemann, “Dicamba Damage Watch,” July 6, 2017, AgPro.

SUMMARY:

Describes the symptoms of dicamba damage – cupped and wrinkled soybean leaves – and other culprits that could be the cause such as other herbicide damage, pests such as aphids and various plant diseases.  It can take 7 to 21 days for dicamba damage to appear, and it will only be evident on new leaves, not those present when the drift occurs.  Percentages as low as 0.06 to 1.9% can cause damage resulting in yield loss. FULL TEXT

Behrens et al., 2007

Mark Behrens, Nedim Mutlu, Sarbani Chakraborty, Razvan Dumitru, Wen Zhi Jiang, “Dicamba Resistance: Enlarging and Preserving Biotechnology-Based Weed Management Strategies,” Science, 316, 2007, DOI: 10.1126/science.1141596.

ABSTRACT:

Abstract: The advent of biotechnology-derived, herbicide-resistant crops has revolutionized farming practices in many countries. Facile, highly effective, environmentally sound, and profitable weed control methods have been rapidly adopted by crop producers who value the benefits associated with biotechnology-derived weed management traits. But a rapid rise in the populations of several troublesome weeds that are tolerant or resistant to herbicides currently used in conjunction with herbicide-resistant crops may signify that the useful lifetime of these economically important weed management traits will be cut short. We describe the development of soybean and other broadleaf plant species resistant to dicamba, a widely used, inexpensive, and environmentally safe herbicide. The dicamba resistance technology will augment current herbicide resistance technologies and extend their effective lifetime. Attributes of both nuclear- and chloroplast-encoded dicamba resistance genes that affect the potency and expected durability of the herbicide resistance trait are  examined.  FULL TEXT

Bohn et al., 2014

T. Bøhn, , M. Cuhra, T. Traavik, M. Sanden, J. Fagan, R. Primicerio, “Compositional differences in soybeans on the market: Glyphosate accumulates in Roundup Ready GM soybeans,” Food Chemistry, 2014, 153, DOI: 10.1016/J.FOODCHEM.2013.12.054.

ABSTRACT:

This article describes the nutrient and elemental composition, including residues of herbicides and pesticides, of 31 soybean batches from Iowa, USA. The soy samples were grouped into three different categories: (i) genetically modified, glyphosate-tolerant soy (GM-soy); (ii) unmodified soy cultivated using a conventional ‘‘chemical’’ cultivation regime; and (iii) unmodified soy cultivated using an organic cultivation regime. Organic soybeans showed the healthiest nutritional profile with more sugars, such as glucose, fructose, sucrose and maltose, significantly more total protein, zinc and less fibre than both conventional and GM-soy. Organic soybeans also contained less total saturated fat and total omega-6 fatty acids than both conventional and GM-soy. GM-soy contained high residues of glyphosate and AMPA (mean 3.3 and 5.7 mg/kg, respectively). Conventional and organic soybean batches contained none of these agrochemicals. Using 35 different nutritional and elemental variables to characterise each soy sample, we were able to discriminate GM, conventional and organic soybeans without exception, demonstrating ‘‘substantial non-equivalence’’ in compositional characteristics for ‘ready-to-market’ soybeans.  FULL TEXT

Bradley, 2018a

Kevin Bradley, “July 15 Dicamba injury update. Different Year, same questions,” University of Missouri, Integrated Pest Management online article, July 19, 2018.

SUMMARY:

First update on 2018 dicamba drift damage.  Reports 1.1 million acres of soybeans damaged, and 605 total complaints across all crops.  FULL TEXT

Cakmak et. al, 2009

Ismail Cakmak, Atilla Yazici, Yusuf Tutus, Levent Ozturk, “Glyphosate reduced seed and leaf concentrations of calcium, manganese, magnesium, and iron in non-glyphosate resistant soybean,” European Journal of Agronomy, 2009, 31:3, 114-119, DOI: 10.1016/e.eja.2009.07.001.

ABSTRACT:

Greenhouse experiments were conducted to study the effects of glyphosate drift on plant growth and concentrations of mineral nutrients in leaves and seeds of non-glyphosate resistant soybean plants (Glycine max, L.). Glyphosate was sprayed on plant shoots at increasing rates between 0.06 and 1.2% of the recommended application rate for weed control. In an experiment with 3-week-old plants, increasing application of glyphosate on shoots significantly reduced chlorophyll concentration of the young leaves and shoots dry weight, particularly the young parts of plants. Concentration of shikimate due to increasing glyphosate rates was nearly 2-fold for older leaves and 16-fold for younger leaves compared to the control plants without glyphosate spray. Among the mineral nutrients analyzed, the leaf concentrations of potassium (K), phosphorus (P), copper (Cu) and zinc (Zn) were not affected, or even increased significantly in case of P and Cu in young leaves by glyphosate, while the concentrations of calcium (Ca), manganese (Mn) and magnesium (Mg) were reduced, particularly in young leaves. In the case of Fe, leaf concentrations showed a tendency to be reduced by glyphosate. In the second experiment harvested at the grain maturation, glyphosate application did not reduce the seed concentrations of nitrogen (N), K, P, Zn and Cu. Even, at the highest application rate of glyphosate, seed concentrations of N, K, Zn and Cu were increased by glyphosate. By contrast, the seed concentrations of Ca, Mg, Fe and Mn were significantly reduced by glyphosate. These results suggested that glyphosate may interfere with uptake and retranslocation of Ca, Mg, Fe and Mn, most probably by binding and thus immobilizing them. The decreases in seed concentration of Fe, Mn, Ca and Mg by glyphosate are very specific, and may affect seed quality.  FULL TEXT

Casteel, 2017

Shaun Casteel, “Soybean Physiology: How Well Do You Know Soybeans?,” 2017, Slide Presentation Prepared for Purdue University Soybean Station.

ABSTRACT: Not Available

FULL TEXT

Davis and Frisvold, 2017

Adam S. Davis, George B. Frisvold, “Are herbicides a once in a century method of weed control?,” Pest Management Science, 2017, 73:11, DOI: 10.1002/ps.443.

ABSTRACT:

The efficacy of any pesticide is an exhaustible resource that can be depleted over time. For decades, the dominant paradigm – that weed mobility is low relative to insect pests and pathogens, that there is an ample stream of new weed control technologies in the commercial pipeline, and that technology suppliers have sufficient economic incentives and market power to delay resistance – supported a laissez faire approach to herbicide resistance management. Earlier market data bolstered the belief that private incentives and voluntary actions were sufficient to manage resistance. Yet, there has been a steady growth in resistant weeds, while no new commercial herbicide modes of action (MOAs) have been discovered in 30 years. Industry has introduced new herbicide tolerant crops to increase the applicability of older MOAs. Yet, many weed species are already resistant to these compounds. Recent trends suggest a paradigm shift whereby herbicide resistance may impose greater costs to farmers, the environment, and taxpayers than earlier believed. In developed countries, herbicides have been the dominant method of weed control for half a century. Over the next half-century, will widespread resistance to multiple MOAs render herbicides obsolete for many major cropping systems? We suggest it would be prudent to consider the implications of such a low-probability, but high-cost development.  FULL TEXT