Fulvic Acid Sprays Shield Wheat From Glyphosate Drift Damage

Glyphosate is the world’s most widely used herbicide, and its spread does not always stop at the edge of the field it is intended to treat. When droplets drift from spraying operations on glyphosate-resistant crops such as canola, they can settle on neighbouring wheat plants, where even sublethal doses trigger stunting, chlorosis and necrosis of young leaves, disrupt nutrient uptake and ultimately depress yield and grain quality. For growers in major wheat-producing regions this is not a hypothetical worry: herbicide drift damage has been documented in the United States and in Australia, where wheat is the largest broadacre crop, with production of 28 million tonnes in 2023–24 contributing 14 percent of total agricultural production value. A new study published in Plant and Soil by Bablu Hira Mandal, Md Hosenuzzaman, Zakaria M. Solaiman and Zed Rengel of The University of Western Australia reports that a humble soil-derived compound, fulvic acid, can substantially blunt that damage when sprayed onto wheat foliage at the right dose and the right time.

The research team set out to test a straightforward hypothesis. Fulvic acid, the water-soluble fraction of humic substances, has long been known to behave like a plant biostimulant: it exhibits phytohormone-like activity, promotes cell elongation, stimulates plasma membrane H+-ATPase, and acts as a strong metal-complexing agent that enhances the uptake of macro- and micronutrients such as magnesium, calcium, iron, copper, manganese and zinc. Because glyphosate is known to disrupt the uptake and translocation of essential elements including calcium, magnesium, iron and manganese even at sublethal doses, the authors reasoned that fulvic acid might counteract several facets of glyphosate injury simultaneously, by supporting growth recovery, restoring nutrient acquisition and possibly stimulating antioxidant defences.

To model the problem, the researchers grew wheat cultivar Scepter in a glasshouse in sandy soil from the Shenton Park field station in Perth, amended with a balanced suite of basal nutrients. In preliminary experiments they simulated glyphosate drift at 1, 3, 5 and 10 percent of the recommended weed-kill rate of Roundup 360, applied with a laboratory boom sprayer at the Zadoks Z13 stage, when wheat seedlings have three leaves. Based on growth and physiological responses, they identified 3 percent of the recommended rate as a representative sublethal drift level near the maximum tolerance threshold, matching field observations that up to 10 percent of the applied herbicide rate can occur as drift under real conditions. All subsequent experiments used this 3 percent dose.

The first suite of experiments screened six fulvic acid concentrations, from 1 to 15 grams per litre, applied either three days before glyphosate or immediately before the herbicide on the same day. Moderate rates of fulvic acid alone were clearly beneficial: at 1 to 5 grams per litre, applied 15 days after sowing, shoot dry weight rose 15 to 22 percent above untreated controls, and 5 grams per litre at that early timing also increased root dry weight and fine root length. Higher rates of 7 to 15 grams per litre provided no growth benefit, and chlorophyll readings actually declined at the highest dose. This dose-dependence echoes a wider literature on humic and fulvic substances, where moderate concentrations typically stimulate growth while excessive amounts can inhibit it.

The protective story became more compelling when fulvic acid was combined with glyphosate. Compared with seedlings receiving glyphosate alone, those sprayed with fulvic acid at low to moderate rates showed significantly higher shoot and root dry weight, longer coarse roots, and higher leaf chlorophyll concentrations measured with a SPAD meter. Timing mattered: applying fulvic acid three days before glyphosate exposure generally outperformed applying it immediately before the herbicide. Shoot micronutrient status also recovered; concentrations of iron, manganese and zinc in shoots were significantly higher in glyphosate-plus-fulvic-acid treatments than in glyphosate alone, consistent with the compound’s established role as a natural chelator that mobilises metal ions within plant tissues.

The most striking result emerged in a third experiment in which fulvic acid was simply mixed into the glyphosate spray tank. Across all mixture treatments, shoot dry weight exceeded that of glyphosate-only plants, total root length returned to control values in almost every case, and chlorophyll concentrations were statistically indistinguishable from untreated seedlings. Glyphosate alone had sharply depressed shoot iron, manganese and zinc, yet the mixtures with 3, 7 or 10 grams per litre of fulvic acid restored iron to levels significantly above glyphosate treatment, while manganese and zinc concentrations rose across all mixtures, often matching the controls. In effect, the presence of fulvic acid in the spray solution appeared to neutralise nearly all visible and measurable glyphosate injury to the wheat seedlings.

Why would mixing the two chemicals be so effective? The authors propose a physicochemical explanation grounded in prior spectroscopy work. At the mildly acidic spray solution pH values measured in the study, between 5.12 and 5.29, both fulvic acid and glyphosate carry predominantly negative charges, but glyphosate’s protonated amine group can form electrostatic bonds with the negatively charged carboxylate groups of fulvic acid. Hydrogen bonding and metal-ion complexation may further promote their association. These interactions could reduce the pool of free glyphosate available for absorption into the leaf and for subsequent phloem-mediated translocation to growing points, thereby limiting the herbicide’s ability to reach and inhibit its target enzyme, 5-enolpyruvylshikimate-3-phosphate synthase, which synthesises the aromatic amino acids tryptophan, phenylalanine and tyrosine. Fulvic acid may also scavenge reactive oxygen species, indirectly reducing oxidative damage. The authors are careful to stress, however, that these mechanisms remain hypothetical in this study because glyphosate uptake, translocation and oxidative stress responses were not directly measured.

The study also revealed that protection is cultivar-dependent. In a fourth experiment, the optimum 5 grams per litre fulvic acid dose was tested on two wheat varieties previously identified as differing in glyphosate sensitivity: Scepter, the most sensitive, and Magenta, the least sensitive of five cultivars screened in earlier work. Magenta outperformed Scepter in shoot dry weight, fine and coarse root length, and micronutrient accumulation. Pre-application of fulvic acid three days before glyphosate raised shoot dry weight to control levels for both cultivars, while same-day application was largely ineffective. The mixture treatment significantly improved root dry weight in both cultivars and enhanced net photosynthetic rate, transpiration and stomatal conductance, with the gas exchange benefits differing between genotypes. A principal component analysis separated treatments into distinct clusters: fulvic-acid-only plants and controls grouped together on the high-biomass, high-photosynthesis side, glyphosate-only plants on the opposite side, and the combined treatments at intermediate positions, together explaining 82 percent of total variation across the measured traits.

The findings arrive at a time when growers and the scientific community increasingly recognise herbicide drift as a persistent agronomic and ecological problem, one that extends beyond wheat to affect native vegetation and non-target plant communities. A foliar biostimulant that is inexpensive, applied at low rates and derived from natural organic matter offers an attractive complement to drift-reduction measures such as nozzle selection, buffer zones and weather-aware spraying. The authors suggest practical implications in two directions. First, prophylactic fulvic acid sprays could be scheduled before likely drift exposure windows, given that pre-treatment proved more effective, presumably because it allows time for physiological and biochemical defence mechanisms to be activated before the stress arrives. Second, the strong protection from tank mixtures is intriguing scientifically but carries a major caveat: if fulvic acid completely eliminates glyphosate’s herbicidal effect, it cannot simply be added to routine weed-control sprays, since that would defeat the purpose of the herbicide.

Important questions remain before fulvic acid can be recommended at field scale. The experiments were conducted under controlled glasshouse conditions at only one drift dose and one growth stage, and the authors explicitly caution that field validation is required before agronomic recommendations can be made. The biochemical and molecular basis of the protection, including antioxidant enzyme responses and metal transporter activity, awaits direct investigation, which the group is pursuing in a separate study. Cultivar-specific responses also suggest that breeding programmes could exploit natural variation in glyphosate tolerance. Still, the core message is clear and pragmatic: timing a fulvic acid spray a few days ahead of anticipated glyphosate exposure, or understanding the chemistry of fulvic acid–glyphosate interactions, could give wheat seedlings a meaningful buffer against one of modern broadacre farming’s most insidious accidental threats.

Subject of Research: Alleviation of glyphosate drift damage in wheat seedlings using foliar fulvic acid application

Article Title: Foliar application of fulvic acid minimises the damage of glyphosate drift to wheat (Triticum aestivum L.) during early growth

Article References: Foliar application of fulvic acid minimises the damage of glyphosate drift to wheat (Triticum aestivum L.) during early growth. (n.d.). https://doi.org/10.1007/s11104-026-09119-w

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09119-w

Keywords: glyphosate drift, fulvic acid, wheat, foliar application, herbicide damage, plant biostimulants, micronutrients, photosynthesis, EPSPS, cultivar tolerance, Plant and Soil, crop protection