Just as we commented on the importance of the order in which crop protection products are mixed and added during the preparation of the spray mixture in the previous post (see "Mixing order of crop protection products"), the incompatibility of crop protection products can occur depending on a number of factors.
Bottle test (or Jar test), an easy and practical tool for assessing the physical and chemical incompatibility of pesticides. Photo: Elevagro, 2013
Before we talk about the main causes of incompatibility between products, we need to understand what types of incompatibility can occur in the mixing of the mixture.
There are basically two types of incompatibility:
1) Chemical Incompatibility
In the context of agricultural spraying, chemical incompatibility is defined as when two or more products are mixed and the product resulting from the mixture presents an incompatibility between the products mixed in such a way as to impair their agronomic efficacy. Chemical incompatibility is not always perceptible to the naked eye and can happen without being noticed at first, only being identified after a failure in the product's efficacy and in the control of the phytosanitary problem.
The best way to know and avoid chemical incompatibility in pesticide mixtures is to follow the manufacturers' recommendations for mixing the products, carrying out physical-chemical analyses (pH, electrical conductivity, viscosity, surface tension, etc.) and evaluating the results of the mixtures' agronomic efficacy. Chemical incompatibility often occurs when there is also physical incompatibility.
The chemical incompatibility of plant protection products can often go unnoticed by the farmer.
Photo: Fast Radius
2) Physical incompatibility
Unlike chemical incompatibility, physical incompatibility is usually visible to the naked eye. Physical incompatibility refers to mixtures of two or more phytosanitary products that present a physical inconformity in the mixture.
Some examples of physical incompatibilities are when there is excessive foaming, crystal formation, phase separation, lumpiness, paste, flocculation and settling in the plant protection mixture. These symptoms of physical incompatibility can also indicate chemical incompatibility, i.e. the loss of agronomic efficacy of the pesticide. In addition to the damage caused by the loss of agronomic efficacy of mixed products (herbicides, insecticides, fungicides, nematicides, fertilizers, etc.), there are also problems related to the accumulation of product in the spraying and supply system and consequent operational failures.
Mixed products that decant, form lumps, floccules and crystals tend to accumulate between hoses, filters, pumps, tanks and other parts of the spraying , mixing and supply systems. In addition to low control efficacy due to possible chemical incompatibilities, the occurrence of physical incompatibility can further reduce agronomic efficacy through the loss of accumulated and clogged products within the systems involved in agricultural spraying or even resulting in errors in flow sensor readings caused by excess foam in the system.
In the same way as chemical incompatibility, it is also recommended to consult the product leaflets as well as the pesticide manufacturers about possible incompatibilities between products in a mixture to avoid future physical incompatibility problems. In addition to consulting the manufacturers, it is always advisable to add the products in the correct order during the preparation of the mixture, adding water before adding the products and mixing constantly, both when mixing and during spraying and transportation of the mixture. Hydraulic agitators with a Venturi system are recommended among the agitators used in sprayers and tanks of batch/fill trucks, guaranteeing constant and uniform agitation. Check out the options of hydraulic nozzles with different flow rates in our store HERE.
Physical incompatibility between phytosanitary products can, in most cases, be avoided by following the correct product mixing recommendations. Photo: Agroefetiva
Main Causes of Physical-Chemical Incompatibility
Among the main causes of incompatibilities seen in the field we can mention:
1 - Lack of knowledge of water quality
Whenever possible, we suggest carrying out physical-chemical analyses of the water on the property, regardless of its source, which will be used for spraying. Remember, don't work in the dark! Find out the pH and hardness of your water. Don't miss out on the effectiveness of your pesticides because you don't know your water. Certain laboratories carry out this type of analysis, but producers can do it themselves. Check out HERE our products for assessing the quality of your water and its mixtures using pH meters, electrical conductivity, temperature, dissolved solids, salinity and more.
2 - Incorrect order of addition to the tank
As we mentioned earlier, the order is essential to minimize the chances of incompatibilities in the tank.
3 - Poor agitation
Poor agitation in the tank of the sprayer/mixer/ready-mix truck at the time of mixing and after mixing (during operation and at times of stoppage - e.g. stops for lunch, rain, maintenance, etc).
4 - Low application volume
All chemical products have a characteristic solubility. If you lower the application volume too much, for example, from 120 L/ha to 50 L/ha, you should be aware of the risk that the plant protection products will not dilute sufficiently in a small amount of water.
This problem has been quite common recently in aerial spraying with drones. Producers who previously used 5 products in ground applications at an application volume of 100 L/ha, for example, are now trying to apply the same 5 products via drone at an application volume of 10 L/ha, i.e. with a mixture that is 10 times more concentrated.
5 - Using incompatible products
Even if all the steps are carried out correctly (order of addition, stirring, appropriate volume of water, etc.), there may still be a risk of product A being incompatible with product B. Consult the manufacturer and check with engineers. Consulting the manufacturer and checking with agronomists, consultants and specialists can be an alternative. Another important way to avoid using incompatible mixtures is to test them on a small scale using the bottle test.
Examples of incompatibilities between herbicides. Markings with X indicate incompatibility and markings with ✓ indicate compatibility. Source: GRDC (2008)
Examples of incompatibilities between herbicides and fungicides, fertilizers and insecticides. Markings with X indicate incompatibility and markings with ✓ indicate compatibility. Source: GRDC (2008)
6 - Not conducting the bottle test (jar test)
The bottle test is an easy, quick and inexpensive way of assessing whether one or more mixtures may present some kind of physico-chemical incompatibility in the field. The test consists of using a container, which can be a PET bottle, a jar or a jug, for example, to simulate the tank of the sprayer or the ready-mix truck. It's a simple way of assessing whether two or more products will be incompatible. Simply add water to the container and add the pesticides in the same order and proportion as they would be added to the sprayer.
Example:
a) Pour 2 liters of water into the pet bottle.
b) Add the first pesticide (solid WG product) in the same proportion as you would use (if its dose is 500 grams in 1 hectare, and I'm applying 100 L per hectare, then its dose in 2 L of water is 10 grams).
c) Add the second pesticide (EC emulsion product) in the same proportion as you would use in the tank.
d) Add the third pesticide and so on.
e) After adding all the products, adjuvants and fertilizers you have tested, close the bottle and shake well.
After shaking the bottle well, leave it to stand in one place and assess whether, after shaking, there has been excessive foaming, whether there has been any settling, flocculation, crystallization or lump formation. After 30 minutes, shake the bottle again and see if there have been any changes. If you wish, carry out these evaluations as many times as necessary and for as long as you think is best to represent your reality.
Example of monitoring two mixtures with different orders of addition, evaluating the syrups before and 18 hours after mixing the products. Source: University of Georgia (2018).
Once all these parameters have been taken into account, the chances of pesticide mixtures being affected by physico-chemical incompatibilities will be drastically reduced.
We hope you all have excellent results in your spraying and that you have a great harvest ahead of you!
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Author:
PhD. Pedro Henrique Urach Ferreira - Spraytech Application Technology Specialist
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