Tank-Mixing Chemicals
Combining pesticides and fertilisers in a tank is a convenient and economical method for simultaneously applying multiple chemicals. When done correctly, this approach can lead to decreased labour and equipment expenses, as well as time and energy savings. Nonetheless, there is a possibility of chemical interactions or alterations to the carrier water that can impact the effectiveness of pesticides in various manners, both positively and negatively.
Negative Effects
Additive effects arise from the inclusion of each added chemical. The cumulative effect is merely the total of the effects that each chemical would produce if applied individually.
Enhancement takes place when an additive is combined with a pesticide to yield a more significant response than when the pesticide is applied alone. Common enhancements in tank mixes often involve the use of adjuvants such as spreaders, stickers, and other materials.
Synergism occurs when the interaction between two chemicals results in heightened effectiveness or control. This may permit the use of lower chemical rates.
Positive Effects
Antagonism represents the opposite of synergism. It arises when the components chemically interact, causing one or both chemicals to become less effective than if they were applied separately. In addition to reduced performance, it can lead to increased plant phytotoxicity.
Incompatibilities can result from either chemical reactions, as mentioned previously, or from the physical outcome of mixing chemicals. For instance, the formation of flocculants can lead to clogging of screens and nozzles, preventing the desired chemical application rate. Additionally, flocculants and precipitants may leave residues on leaf surfaces. Other chemical incompatibilities may stem from mixing chemicals with unsuitable carrier water. Water with pH levels that are either too low or too high, along with extreme temperatures or containing salts and organic particulates, can chemically alter the compound to be applied.
Pesticide resistance to two or more chemicals in a tank mix can develop if the same chemical combination is repetitively used over an extended period. Pests may build resistance more quickly when chemicals within the same tank mix share the same mode of action. For example, both cyfluthrin and bifenthrin belong to the synthetic pyrethroids class and target the same site in an insect’s nervous system. Resistance can also develop when chemicals have different modes of action if they are used frequently.
To make sure that only positive effects occur when tank-mixing, follow these guidelines for developing new tank-mixes:
- Know the temperature, pH and salinity of your carrier water. Adjust your carrier water temperature and pH to the optimal range of each chemical before mixing in a spray tank or for a jar test.
- Read the label of all chemical products considered to be tank-mixed. The product labels will give you information on what type of chemical and carrier to avoid and potential problems that may occur. If you are still unsure about a mix, contact the manufacturer.
- Perform a jar test following proper mixing procedures (see below). This will determine physical incompatibilities.
- Many chemicals require constant agitation; be sure to follow all label instructions. Many labels will instruct you in the sequence for adding products to the tank mix.
- Tank-mix enough to make a test application on part of the target site (preferred) or on a non-target site. Schedule the application to allow enough time for any negative effects (chemical incompatibilities) to be apparent before the actual application is made.
- When making an actual application, spray as soon as possible. Do not use a spray solution that has been sitting for a long time. Some chemicals may degrade in spray solution after several hours.
Performing a Jar Test
Always wear label recommended personal protective equipment (PPE) when handling any chemical. When working with mixes of chemicals, you must wear the PPE recommended on the label of the most toxic material in the mixture.
Step 1: Measure half a litre of carrier water in a clear 1 litre jar that is not used for any other purpose.
Step 2: Add ingredients in the proper mixing order (Table 1), stirring each time a new chemical is added. Check for the formation of foam, scum or precipitates after adding each ingredient. It is sometimes necessary to premix some chemicals (some wettable powder (WP), dry flowable (DF), water-dispersing granule (WDG), or liquid flowable formulations as indicated on the labels) before adding to the spray tank. Do not mix the chemicals together without dilution before adding to the jar or spray tank.
Step 3: Let the mixture sit for 15 minutes. Check for foam, scum and precipitates and other unexpected results or appearance (for example, wettable powders will not dissolve). Feel the side of the jar to gauge temperature. If it is warm, let the jar sit and recheck in another 15 minutes.
| Order of addition | Chemical | Amount of Jar Test (per 378 litres) of final spray volume) |
| 1 | Water conditioning agents and activators | 2 teaspoon per litre |
| 2 | Wettable powders and dry flowable | 2 tablespoon per kg |
| 3 | Water soluble concentrates or solutions | 2 teaspoon per litre |
| 4 | Emulsifiable concentrates | 2 teaspoon per litre |
| 5 | Soluble powders | 2 teaspoon per litre |
| 6 | Surfactants and oils | 2 teaspoon per litre |
| 7 | Fertilisers | proportional |
