Foliar uptake of pesticides : Present status and future challenge

The current chronic kidney disease epidemic, the major health issue in the rice paddy farming areas in Sri Lanka has been the subject of many scientific and political debates over the last decade. Although there is no agreement among scientists about the etiology of the disease, a majority of them has concluded that this is a toxic nephropathy. None of the hypotheses put forward so far could explain coherently the totality of clinical, biochemical, histopathological findings, and the unique geographical distribution of the disease and its appearance in the mid-1990s. A strong association between the consumption of hard water and the occurrence of this special kidney disease has been observed, but the relationship has not been explained consistently. Here, we have hypothesized the association of using glyphosate, the most widely used herbicide in the disease endemic area and its unique metal chelating properties. The possible role played by glyphosate-metal complexes in this epidemic has not been given any serious consideration by investigators for the last two decades. Furthermore, it may explain similar kidney disease epidemics observed in Andra Pradesh (India) and Central America. Although glyphosate alone does not cause an epidemic of chronic kidney disease,

https://www.infosperber.ch/data/attachements/Glysophat_Studie_Sri%20Lanka.pdf

Glyphosate, Hard Water and Nephrotoxic Metals: Are They the Culprits Behind the Epidemic of Chronic Kidney Disease of Unknown Etiology in Sri Lanka?

https://research.sabanciuniv.edu/13147/1/2009_Glyphosate_reduced_seed_and_leaf_concentrations_of_calcium_etc.pdf

Glyphosate reduced seed and leaf concentrations of calcium, manganese, magnesium, and iron in non-glyphosate resistant soybean

Summary
The recent visualization of stomatal nanoparticle uptake ended a 40-yr-old paradigm. Assuming clean, hydrophobic leaf surfaces, the paradigm considered stomatal liquid water transport to be impossible as a result of water surface tension. However, real leaves are not clean, and deposited aerosols may change hydrophobicity and water surface tension.
Droplets containing NaCl, NaClO3, (NH4)2SO4, glyphosate, an organosilicone surfactant or various combinations thereof were evaporated on stomatous abaxial and astomatous adaxial surfaces of apple (Malus domestica) leaves. The effects on photosynthesis, necrosis and biomass were determined. Observed using an environmental scanning electron microscope, NaCl and NaClO3 crystals on hydrophobic tomato (Solanum lycopersicum) cuticles underwent several humidity cycles, causing repeated deliquescence and efflorescence of the salts.
All physiological parameters were more strongly affected by abaxial than adaxial treatments. Spatial expansion and dendritic crystallization of the salts occurred and cuticular hydrophobicity was decreased more rapidly by NaClO3 than NaCl.
The results confirmed the stomatal uptake of aqueous solutions. Humidity fluctuations promote the spatial expansion of salts into the stomata. The ion-specific effects point to the Hofmeister series: chaotropic ions reduce surface tension, probably contributing to the defoliant action of NaClO3, whereas the salt spray tolerance of coastal plants is probably linked to the kosmotropic nature of chloride ions.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.2012.04307.x

Stomatal penetration by aqueous solutions – an update involving leaf surface particles

Field experiments were conducted from 1993 to 1995 to compare weed control by the isopropylamine salt of glyphosate at 0.21, 0.42, 0.63, and 0.84 kg ae/ha applied at three stages of weed growth. Weed control by glyphosate applied at these rates alone or with ammonium sulfate at 2.8 kg/ha was also evaluated. In other experiments, potential interactions between glyphosate and acifluorfen, chlorimuron, and 2,4-DB were evaluated. Velvetleaf, prickly sida, sicklepod, pitted morningglory, entireleaf morningglory, palmleaf morningglory, and hemp sesbania were controlled more easily when weeds had one to three leaves compared with control when weeds had four or more leaves. Glyphosate controlled redroot pigweed, velvetleaf, prickly sida, sicklepod, and barnyardgrass more effectively than pitted morningglory, entireleaf morningglory, palmleaf morningglory, or hemp sesbania. Increasing the rate of glyphosate increased control, especially when glyphosate was applied to larger weeds. Greater variation in control was noted for pitted morningglory, palmleaf morningglory, prickly sida, and velvetleaf than for redroot pigweed, sicklepod, entireleaf morningglory, or hemp sesbania. Ammonium sulfate increased prickly sida and entireleaf morningglory control but did not influence sicklepod, hemp sesbania, or barnyardgrass control. Acifluorfen applied 3 d before glyphosate or in a mixture with glyphosate reduced barnyardgrass control compared with glyphosate applied alone. Chlorimuron did not reduce efficacy. Mixtures of glyphosate and 2,4-DB controlled sicklepod, entireleaf morningglory, and barnyardgrass similar to glyphosate alone.

Influence of application variables on efficacy of glyphosate

Glyphosate toxicity to wheat was antagonized more by calcium chloride than sodium bicarbonate. Mixtures of the salts at greater than 100 mg L−1 sodium bicarbonate and 200 mg L−1 calcium chloride were additive in antagonism of glyphosate in the greenhouse experiments. Surfactant and oil adjuvants did not overcome sodium bicarbonate or calcium chloride antagonism of glyphosate. Oil adjuvants were generally antagonistic to glyphosate. An equation is presented that determines the amount of diammonium sulfate required to overcome glyphosate antagonism based upon the sodium, potassium, calcium, and magnesium cations in the spray carrier.

Optimizing Adjuvants to Overcome Glyphosate Antagonistic Salts

Diammonium sulfate is commonly used as an adjuvant with glyphosate, but reports vary regarding its effect on weed control, and its possible function in enhancing glyphosate phytotoxicity is not fully understood. Several experiments were conducted in the glasshouse to determine glyphosate phytotoxicity to various species as influenced by diammonium sulfate in distilled water and in the presence of antagonistic salts. Diammonium sulfate overcame sodium hydrogen carbonate, calcium chloride, and 2,4-D antagonism of glyphosate phytotoxicity to wheat (Triticum aestivum L.). Sulfate anions were important for overcoming calcium antagonism, possibly by forming calcium sulfate

Influence of diammonium sulfate and other salts on glyphosate phytotoxicity

Scanning electron micrographs of spray droplet residual on wheat, sunflower, and kochia indicated that salts and various adjuvants applied with glyphosate affected deposit crystal content, thickness, and contact with the leaf surface. Spray deposits of glyphosate applied with diammonium sulfate contained distinct crystals, which related to enhanced toxicity of glyphosate applied alone, or to overcoming antagonism of glyphosate toxicity by calcium chloride, when applied to wheat. In general, glyphosate applied with antagonistic calcium chloride salt formed spray deposits that were amorphous, thick, and without crystals. Glyphosate sprayed with nonantagonistic diammonium sulfate and ammonium chloride salts had deposits with crystals and an evenly spread residue beneath the crystals. The various micrographs indicate that the antagonism of glyphosate phytotoxicity by salts may be in part from physical entrapment of glyphosate in the spray deposit. Glyphosate spray droplet residue contact with wheat, sunflower, and kochia surfaces related to observed differences in glyphosate toxicity to these species.

Spray droplet residual of glyphosate in various carriers.

Calcium chloride in the spray carrier antagonized the toxicity of diethanolamine 2,4-D and sodium 2,4-D, dimethylamine MCPA, sodium bentazon, dimethylamine dicamba and sodium dicamba, sodium acifluorfen, imazamethabenz, ammonium imazethapyr, and isopropylamine glyphosate to kochia in greenhouse experiments. Diammonium sulfate overcame calcium chloride antagonism of the above herbicides, except for glyphosate and imazethapyr. Diammonium sulfate or ammonium nitrate adjuvants overcame calcium chloride and sodium bicarbonate antagonism of dicamba toxicity to kochia and enhanced toxicity of sodium dicamba to nearly equal that of dimethylamine dicamba.

Spray Carrier Salts Affect Herbicide Toxicity to Kochia (Kochia scoparia)

Species Differ in Response to Adjuvants with Glyphosate

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