Beyond Sulfur: Viticultural Foliar Spray Programs

Beyond Sulfur: Viticultural Foliar Spray Programs

The needling sensation started in the vineyard at Beaux Frères. I was walking next to winemaker Mike Etzel Jr., scribbling notes as he talked about biodynamic farming, when a tractor pulled up. Etzel ran into a shed, grabbed a carton of a mysterious orange liquid, a bag of powder, and a measuring jug; he mixed the powdered sulfur and water, threw a running hose into the spray tank on the tractor, added the sulfur slurry, and measured out and added the liquid.

While Etzel finished filling the spray tank, I stared skeptically at the cast-aside container of orange liquid: OROBOOST, Active Ingredient: Alcohol Ethoxylate 13.58%. Despite years studying wine, I realized that the only thing I really knew about spray programs was that elemental sulfur treats powdery mildew and, when combined with copper and lime for Bordeaux mixture, it treats downy mildew.

There is a common misconception that additives to a spray tank are negative—see my above skepticism at orange liquid. The reality is that efficient and effective spray programs are how agriculture functions to turn out the quality and quantity that consumers expect. Further, it is only through understanding the categories of agricultural chemicals and their functions that it becomes possible to replace environmentally harmful products with less-harmful alternatives or to increase efficiency and decrease application rates.

Maximizing Efficiency: The Role of Adjuvants

So how might a viticulturist start maximizing efficiency? One of the most critical aspects of a spray program is full target coverage. Spray operators spend an immense amount of time ensuring that they have calibrated their sprayers to the correct pressure and target width to fully cover the vine canopy. But all this meticulousness can end up down the French drain without a proper spray mix, and this was what Etzel was creating.

OROBOOST is the brand name of an organic and biodynamic-approved adjuvant. Adjuvant is a fancy word for anything that modifies a spray solution to make an herbicide, insecticide, miticide, fungicide, or foliar nutrient spray more effective. An adjuvant might, for example, increase the adhesiveness of a spray mix or slow drying time so that active ingredients remain available longer. Biodynamic, organic, and conventional growers all use adjuvants because, when paired correctly with the product they are applying in sprays, adjuvants increase effectiveness by 30% to 50% and can decrease the rate of application. When paired incorrectly, however, an entire year’s crop can be lost to phytotoxicity. Because of the complicated reactions that occur when adjuvants and other products are mixed, many formulations are available premixed. When producers declare that they don’t use adjuvants, the adjuvant is often already present in their sulfur formulations, which are usually mixed with anything else they are spraying (the exception is if they dust sulfur instead of spraying). There are currently over a dozen categories of adjuvants and hundreds of products available. The following are the most important adjuvants for viticulture. Other examples are drift retardants, defoaming agents, compatibility agents, emulsifiers, extenders, scents, marking agents, UV protectants, and tank cleaners.


Also known as spreaders or wetters, surfactants (a contraction of surface-acting agents) increase effectiveness by lowering the surface tension of spray droplets. Imagine a droplet of water on an iPhone screen and, next to it, a droplet of distilled alcohol. The water droplet beads. The alcohol clings. This modification of surface tension is what happens when a surfactant is incorporated into a spray mix, helping it adhere to the plant’s surface and thus increasing spray efficiency and decreasing runoff. Some of the most common active ingredients for brand-name surfactants are ethoxylated fatty alcohols (e.g., OROBOOST and VINTRE) and alkyl polyglucosides (e.g., OVS 90 NIS), compounds that can also be found in some laundry detergents, shampoos, and cosmetics. But these are far from the only active ingredients that can be used. Recently, surfactants using trisiloxane have been developed; these are referred to as organosilicones (e.g., Freeway).

While there are many commercially available organic and biodynamic surfactants, like OROBOOST, there are producers who would prefer a botanically derived option. This has led to manufacturing of biosurfactants from plants rich in a metabolite called saponin. Examples include soapbark (Quillaja saponaria), yucca (Yucca schidigera), tea seed (Camellia oleifera), and quinoa (Chenopodium quinoa). While these have proven effective, the molecular and chemical structures of saponins differ based on how and where a plant is grown and how the saponin is extracted. This makes it difficult to produce a consistent product that can be reliably measured for mixing with herbicides, insecticides, miticides, fungicides, or foliar nutrient sprays for predictable results. Research into this is ongoing, but manufacturers that have managed to produce a consistent product, such as Therm X-70, derived from yucca, have experienced increased demand in recent years.

Oil-Based Adjuvants

Oil slows the evaporation of whatever is being delivered in a spray, which increases the amount of time the ingredient is available and the potential for absorption. Oils (along with surfactants, which decrease evaporation) are often referred to as penetrants. Most of these formulations are petroleum-based crop oils (e.g., Wilbur-Ellis MOR-ACT), methylated seed oils (e.g., Alligare MSO 1), mineral oils (e.g., Vicchem AD-HERE), and vegetable oils (e.g., Codacide). Generally, a percentage of surfactant is added to oil adjuvants to make them easier to mix with water.

Oil-based formulations cannot be combined with sulfur, as oil and sulfur react, forming phytotoxic chemicals and damaging plant tissue. Usually, applicators are told to leave 10 days between oil sprays and sulfur sprays. Oils often take on two roles, smothering certain insects and fungal diseases in addition to their role as an adjuvant.

Buffers and Acidifiers

Most products have a pH range that maximizes effectiveness. Pesticides tend to be most effective in acidic solutions with a pH between 4.5 and 6.5. If the solution becomes alkaline, the pesticide can be rendered ineffective. Thus, acidifiers, often a form of citric acid with additives, can be added (e.g., SaferGro pH Down). Acidifiers don’t guarantee that a solution will stay at a constant pH. For this, a buffer, a weak base or acid, most often in the form of a phosphate salt, is needed (e.g., VAS Buffer Xtra Strength).

Fertilizer Adjuvants

Ammonia-based fertilizers have been shown to increase the effectiveness of some herbicides, including glyphosate salts. Ammonia sulfate (AMS) can also serve as a water conditioner, removing chemicals that may impact performance. When AMS is combined with hard water that has high levels of calcium carbonate, for example, it will form calcium sulfate. Then, when the herbicide is added, the stabilized calcium will not precipitate out the active herbicide ingredients.


Stickers, also known as deposition aids, increase the adhesion of a spray to the plant material. In addition to helping with absorption, these products can form a film that helps with weatherproofing active ingredients. Many products use latexes, resins, or fatty acids as the so-called sticker. Stickers are often combined with surfactants to form spreader-stickers. Miller Nu-Film P is a common spreader-sticker that can be used by organic and biodynamic growers. Pinene, a pine-derived terpene, is its main sticker.


Much like oil-based adjuvants, humectants slow the drying time of spray deposits. Unlike oils, humectants do this by increasing water retention. The most used humectants in agriculture are sugars and salts. Fructose, glycerol, and glycol derivatives are used as humectants, as are fertilizer salts like AMS. Molasses has been used as a humectant since 1984, and many old-school organic practitioners swear by its efficacy.

The Two Parts of Spray Programs

Most foliar spray programs can be considered in two parts: sprays targeting pest and fungal pressure, and sprays providing foliar nutrients. Sprays for pest and fungal pressure are often broad-spectrum, a term that refers to a product’s ability to act on multiple pressures at once. Often, these can be combined with foliar nutrient sprays. Both parts of foliar spray programs can be found in biodynamic, organic, and conventional vineyard management.

Before devising any spray program, a viticulturist must understand seasonal pressures and nutrient requirements for their specific site. This involves observation and research to determine which pests and fungal diseases are most prevalent, as well as soil and tissue sampling to see which micro- and macronutrients are present in the soil and in plant tissue.

Part 1: Targeting Seasonal Pest and Fungal Pressure

Plant protection products, or PPPs, are used to address seasonal pest and fungal pressure, which viticulturists begin evaluating at budding. At this point in the season, eriophyid mites (bud, rust, erineum), thrips, and the fungal disease Phomopsis (where present) are often the biggest concerns. These pressures are generally treated with a preventative sulfur spray. But if Phomopsis is known to be present in a conventionally managed vineyard, a systemic contact fungicide (e.g., Ziram Xcel, Manzate, or BASF Cygnus) might be used. If there is little or no pressure, sprays might be deemed unnecessary.

From when the vine reaches around 12 centimeters of growth and until veraison, powdery mildew is the leading pressure in vineyards globally. Botrytis, downy mildew, and various pests (such as eriophyid mites, spider mites, leafhoppers, mealybugs, moths, borers, and beetles) can also pose issues. Viticulturists often spray treatments on a 7-to-21-day interval, with length of the interval dependent on fungicide choice and weather. Others have adopted spore-trapping systems that allow monitoring of powdery mildew through weekly testing. This has given growers a much better understanding of the powdery mildew life cycle, and negative test results give some growers the confidence to delay sprays or to skip them altogether.

From veraison to harvest, the threat of powdery mildew lessens, because there is no new green tissue to infect. The main pressures during this period are botrytis and insects. As growers are advised to avoid spraying with sulfur close to harvest, if there is risk of botrytis infection or insect infestation, they must rely on an alternate formula that has a short preharvest interval. If a vineyard had heavy botrytis infection, heavy powdery mildew, or Phomopsis, growers may opt to spray lime sulfur products during dormancy to kill overwintering spores.

As powdery mildew is the largest pressure, and it has yet to develop a resistance to sulfur, sulfur is the backbone of viticultural spray programs. Yet there are many other options available, including products with broad-spectrum effects similar to those of sulfur. These are some of the most common, but this is by no means an exhaustive list. From tobacco teas to synthetic neonicotinoids, powder from pyrethrum flowers to pyrethroids, chemical companies are very good at taking botanical solutions and creating more powerful synthetic pesticides and fungicides. New products hit the market every year.

Horticultural Oils

Horticultural oils are one of the only eradication methods for powdery mildew; most controls are best used preventatively. Typically based on organic mineral oil from distilled petroleum (e.g., Intelligro PureSpray GREEN, JMS Stylet-Oil), these oils can also be derived from botanicals. Neem oil, which contains a naturally occurring chemical called azadirachtin, kills most soft-bodied insects (this includes aphids, mealybugs, whiteflies, Japanese beetles, leafhoppers, thrips, fungus gnats, spider mites, and nematodes). Cinnerate, a cinnamon oil–based product, touts increased efficiency as a miticide. Most horticultural oils are broad-spectrum, and their effect on beneficial insects should be considered. Sulfur and horticultural oils can be rotated, but a 10-day minimum between sprays is recommended.

Systemic Fungicides

Systemic fungicides get a bad rap for good reason. They are most often used in large-scale conventional agriculture to extend spray intervals so that fewer passes are necessary. Their long-lasting effect is owed to absorption into plant tissue. If they are overused, and if the same systemic fungicide class is used too often, powdery mildew can become resistant. Operators must rotate their chemistries, using a different class (with a different mode of action) each time they spray. Because operators are not always meticulous in their use of chemistries, resistance can be developed, necessitating the use of harsher chemicals.

Systemic fungicides can, however, be used responsibly. In December 2022, Richard Leask, director of Leask Agri, in McLaren Vale, was facing one of the wettest and highest downy mildew pressure seasons he’d ever seen. “At this point in the season, we’ve usually had 30 millimeters of rain,” he says. “This year [we’d] had 130. It’s the first time in 15 years that I’ve had to spray anything other than sulfur and copper.” In addition to the compaction and safety risks of taking a tractor out in this amount of rain, the efficacy of a regular contact fungicide spray like sulfur and copper would last a few days at most. “It really comes down to if we’d be willing to wear the loss of harvest,” explains Leask. “We can’t make that bargain.” The product that he selected, Ridomil Gold Copper, uses mefenoxam and copper hydroxide for broad-spectrum impact, treating the high downy mildew pressure as well as the possibility of powdery mildew.

Classes of systemic fungicide include demethylation inhibitors, strobilurins, quinolines, benzophenones, phenylacetamides, and multiclass formulations.


Biofungicides are formulations of living fungi, bacteria, or actinomycetes that are specially selected and isolated to hinder plant pathogens by competing with or parasitizing other fungi, producing antibiotic substances, or inducing an immune response in the vine itself. Drew Herman, the vineyard manager at J.K. Carriere Wines, in Oregon’s Willamette Valley, points out that products sold as biofungicides are just isolated, concentrated strains of natural microorganisms that grow in compost and can be readily sprayed via compost teas. For this reason, he prefers to spray compost tea, using molasses as an adjuvant. Other sustainably minded growers find that increasing the population of certain biological controls helps them at different times in the year. Troon, in southern Oregon, uses the biopesticide Bacillus thuringiensis (Bt) to control insects in its on-site gardens, while Bacillus subtilis, in the form of AVIV, performs well as a powdery mildew control when temperatures start to rise later in the season but aren’t high enough to kill spores. Though downy mildew is not an issue on the West Coast, Bacillus subtilis has been shown to have some effect on downy mildew in other areas of the world, in addition to being effective against botrytis.

Commercially available biofungicides include AVIV and Serenade (Bacillus subtilis), SONATA (Bacillus pumilus), Double Nickel (Bacillus amyloliquefaciens), Howler (Pseudomonas chlororaphis), and Regalia (Reynoutria sachalinensis). Though it is not based on a microorganism, ProBlad Verde (Banda de Lupinus albus doce), is a protein from sweet lupines that functions as a broad-spectrum biofungicide. Biofungicides and biopesticides vary widely in whether they are broad-spectrum or targeted.

Milk Sprays

Though uncommon, milk and whey treatments are effective against powdery mildew when sprayed in sunlight. This is attributable to the production of oxygen radicals and the presence of the antimicrobial compound lactoferrin. In Oregon, the vineyard at Niew Vineyards, owned by Tai-Ran Niew, has recently entered grape production; during its establishment, Niew used only milk for powdery mildew protection.

Potassium Bicarbonate

Typically employed as a preventative treatment, potassium bicarbonate (baking soda) mixed with nondetergent soap or oil (as an adjuvant) has been used by rose farmers since at least 1992, when a study conducted by Cornell University helped validate this method. It is now offered in wettable applications (premixed with adjuvant) from Brandt Kaligreen and BioWorks MilStop SP.

Part 2: Addressing Deficiencies

Applying Foliar Nutrients

Macronutrient levels (nitrogen, phosphorous, potassium, and magnesium) are generally addressed through soil treatments. Micronutrients, however, often appear in foliar nutrient applications. Without sufficient levels of micronutrients, vines can show decreased growth and yield and may be more susceptible to disease. An understanding of which nutrients are used for what function, and at which point in a plant’s life cycle, is critical for effective nutrient sprays. Drew Herman points out that vines will often test as deficient in certain mineral nutrients when, in fact, the soil has plenty of that nutrient, but it’s not the stage in the life cycle where the plant is using the nutrient. “Petiole testing only looks at what’s being transported at that moment,” he explains. “You need sap analysis and soil analysis.” Once growers determine which nutrients are necessary, they can usually be applied in conjunction with PPPs.

Boron, iron, manganese, zinc, and molybdenum are among the key micronutrients for vines. Boron is important for root growth and bud development. If vines are found to be deficient, spraying a formulation such as Solubor foliar fertilizer two to three weeks before bloom is recommended. Iron is used for photosynthesis, respiration, chlorophyll formation, and cell strengthening. It can be applied as a chelated iron spray near bloom for minor deficiencies. Manganese is used for synthesizing chlorophyll and fatty acids; it is also involved in photosynthesis. Deficiencies can be treated with a foliar application of manganese sulfate around bloom, perhaps continuing into the growing season.

Zinc is critical for the formation of auxins (which regulate plant growth), chloroplasts, and starch. Without zinc, plant growth will be stunted, and vines may not set fruit. Zinc can be applied in foliar applications throughout the growing season. Finally, molybdenum is essential to vine growth. It is rarely deficient but, if needed, can be corrected with foliar nutrient sprays around bloom.

Alternative Views

Foliar micronutrient sprays are somewhat controversial. Many sustainably leaning growers choose not to use them and attempt to correct for deficiencies through alternative methods. Drew Herman believes that there are several factors that must be taken into account before spraying micronutrients, including a site’s soil pH and microbial health. He explains that in the Willamette Valley, low pH soils lead to increased aluminum uptake, which can cause phytotoxicity. To decrease aluminum uptake, many growers will add calcium to their soils, but this affects magnesium uptake, so they spray with magnesium. Herman wants to limit inputs, and, while it’s a slower process, he’s found that this is best accomplished through liming the plant. He explains, “I’ll apply wollastonite, a calcium silicate, along with compost tea. The microbes in compost are what carry deliverables like calcium into the plant. Silica is highly mobile, and so by liming the plant, we can slowly change the pH of the soil through root exudates.” This approach has the added benefit of thickening plant cell walls, which is helpful in guarding against fungal infection. The microbes present in the compost tea, in addition to assisting in transport, compete with powdery mildew.

Troon’s viticulturist, Jason Cole, and director of agriculture, Garett Long, also use silica but in a different form. As their property is biodynamic, they apply the horn silica prep 501, a ground paste of silicon dioxide that has been buried in a cow’s horn. While silicon isn’t generally considered an essential micronutrient by winegrowers, Cole argues that it should be and echoes Herman in emphasizing its ability to thicken cell walls and strengthen plants. Another natural application is liquid kelp spray, which can be used to address potassium deficiency or as a stimulant; at Troon, it is used in small quantities early in the season, along with very small amounts of zinc, boron, and manganese. At Troon, most nutrition is provided by compost applications.


Foliar spray programs are multifaceted and, even in their most basic form, require a high level of knowledge for seamless execution. In addition to knowing how to apply sprays for full coverage, applicators must understand the nuances of adjuvants and the ways that plant protection products might react with other PPPs in the spray tank. By paying close attention to seasonal pressures and nutrient requirements, viticulturists can eliminate unnecessary sprays, saving on product and lessening runoff that can have negative effects on the surrounding ecosystem. Further, with increased experience, applicators may gain the confidence to trial gentler products on small sections of vineyard, observing if they are suitable replacements for products containing harsher active ingredients. More sustainably minded growers may realize that in cases of high fungal or pest pressure, one pass with a harsher PPP is preferable to a gentle product to curb a possible outbreak of fungal disease or a pest that could become a consistent threat to fruit quality. In all cases, increased knowledge allows for more efficient, effective, and—if the producer is prioritizing it—environmentally sustainable programs.

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  • Very well written Samatha. Thanks for introducing this subject to a broader audience. Important (and quite nuanced) stuff!

  • Chris, I really appreciate this! It seems to me that the farther away a practice is from the consumer experience, the easier it becomes to dismiss or disregard. I think the importance is what you say, the industry needs to understand so that we're better able to educate and correct in the case that the consumer narrative (or even the industry narrative) becomes 'sprays are negative.' Bummed that I won't see you at MW seminar this week but look forward to seeing you soon!

  • GOLD! Samantha you are an alchemist! Taking a seemingly scary and unnecessary practice and turning into a brilliant and digestible essay. It is so important for all of us in the wine industry, especially those in sales, to read and understand the high level of precision involved in viticulture. Too often do people just wave the magical wide brush of terms like sustainable, BD, and OG viticulture, show some pictures of clover and move on with their day. Bravo on a truly important piece.