Tank mix additives
Tank mix additives, mainly with herbicides, are increasingly used in World.
The expected benefits are dose reduction, efficacy adjustments and drift limitation. By mode of action, three main families can be distinguished: surfactants, oils and salts. Surfactants reduce the surface tension of the spray liquid and can also promote absorption of the active ingredients into the leaves. Oils above "penetrants" are mainly compatible with lipophilic active ingredients, such as specific graminicides. Salts are better hygroscopic and beneficial with hydrophilic active ingredients such as bentazone, glufosinate or glyphosate.
The expected benefits are dose reduction, efficacy adjustment and drift limitation. According to the mechanism of action, three main families can be distinguished: surfactants, oils and salts. Surfactants reduce the surface tension of the spray liquid and can also help to absolutize the active ingredients in the leaves. Oils are penetrants generally compatible with lipophilic active ingredients such as specific graminicides. Salts are better hygroscopic and beneficial with hydrophilic active ingredients such as bentazone, glufosinate or glyphosate.
Synergism (Crop damage)
When products synergize, the application becomes too potent. For example, an adjuvant could affect crop retention or uptake, exposing it to more active ingredient or overwhelming crop metabolism. The result is damage to the crop we are trying to protect.
Antagonism (Reduced efficacy)
When products antagonize, the application becomes less potent. There are several examples:
pH adjusters in one product may reduce the half-life of another product (e.g. The fungicide Captan has a half-life of 3 hours at a pH of 7.1 and only 10 minutes at a pH of 8.2.)
Active ingredients may get tied-up on the clay-based adjuvants in other products (e.g. glyphosate tied up by Metribuzin).
One product changes the uptake/retention of another. For example, a contact herbicide burns weed foliage beyond its ability to take up a lethal dose of systemic herbicide.
Physical incompatibility affects work rate and efficacy. Products form solids that interfere with or halt spraying. It can also make sprayer clean-up more difficult. For example, weak-acid herbicides lower the pH of the spray mix, reducing the solubility of Group 2 herbicides (i.e. imidazolinones, sulfonylureas, sulfonanilides). The oily formulation then adheres to plastic and rubber surfaces in tanks, connectors and hoses.
There are many forms of physical incompatibility:
Liquids can curdle into pastes and gels that clog plumbing to such an extent that flushing cannot clear it and a manual tear down is required.
Dry formulations don’t hydrate or disperse, becoming sediment that clogs screens and nozzles. Even if they are small enough to spray, they reduce coverage uniformity. For example, a dry product added behind an oil gets coated, preventing it from hydrating.
Certain product combinations may cause settling, or one partner is more prone to settling. If the sprayer sits without agitation, settled products may or may not resuspend.
Certain product combinations may cause foaming, or one partner may be prone to foaming, causing overflows or breaking pump suction. When products foam, dry products added through the foam may swell, preventing hydration.
Phase separation occurs when products layer in the tank. Consider oil and water. Even with agitation, the active ingredients may not be uniformly suspended in the tank and coverage uniformity will be reduced during spraying.
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