Rational tank-mixing of pesticides can improve control efficacy, delay the development of pest and disease resistance, raise the level of control and reduce the amount of product used; mixing products aimed at different pests and diseases can also cut the number of applications, thereby lowering labour costs.
But if the mix is unreasonable it can be dangerous — at best the efficacy is lost, at worst crop injury occurs.
Order of mixing
(1) The order of mixing must be correct. The usual order for mixing foliar fertilisers and pesticides is: micronutrient fertiliser, water-soluble fertiliser, wettable powder, water-dispersible granule, suspension concentrate, micro-emulsion, emulsion in water, water, emulsifiable concentrate, added in that order (in principle no more than three pesticides should be mixed). After adding each one, stir thoroughly until homogeneous, then add the next.
(2) Add water first, then the product. For two-stage dilution, it is advisable to put about two-thirds of a tank of water into the sprayer first and mix in the first pesticide. Then pre-dilute the remaining pesticide in a plastic bottle, pour the diluted product into the sprayer and mix well, and so on (do not cut corners if you want good efficacy).
(3) Whatever you mix, remember: "mix fresh and use immediately; do not leave standing for long". Although the spray liquid may show no reaction when first mixed, that does not mean it can be left standing indefinitely, otherwise slow reactions can occur and efficacy will gradually decline.
Principles of tank-mixing
● Mix pesticides with different modes of toxic action: mixing products with different modes of action can improve control efficacy and delay the development of resistance.
● Mix pesticides with different modes of toxic effect: insecticides may act by contact, stomach poison, fumigation or systemic action, and fungicides by protectant, curative or systemic action. Mixing products with different modes of control lets them complement each other and produces very good results.
● Mix insecticides that act on different life stages: this can kill pests at all their stages in the field, giving thorough control and thus improving efficacy.
● Mix pesticides with different persistence profiles: some are fast-acting with good initial control but short residual activity; others have weaker initial control but long duration. Mixing them gives both good control after application and long-term protection.
● Mix with synergists: synergists have no direct toxic effect on pests and diseases, but mixed with pesticides they can improve control efficacy.
● Mix pesticides aimed at different pests and diseases: when several pests and diseases occur at the same time, this approach can reduce the number of sprays and working hours, thereby raising efficiency.
Points to note when tank-mixing
Tank-mixing has many advantages, but must never be done at random. Unreasonable mixing is not only useless but counterproductive. The following points must be observed.
● Do not alter physical properties
That is, after mixing there must be no floating oil, flocculation, sediment or discolouration, and no heat generation or bubbling. If all products are powders, or all granules, fumigants or smoke generators, they can generally be mixed; but between different formulations — wettable powders, emulsifiable concentrates, concentrated emulsions, suspension concentrates, water-soluble liquids and other water-based liquids — arbitrary mixing is not advisable.
● Do not cause chemical change
(1) Many products cannot be mixed with alkaline or acidic pesticides. Under alkaline conditions such as Bordeaux mixture or lime sulphur, carbamate and pyrethroid insecticides, and dithiocarbamate fungicides such as thiram and zineb, readily undergo hydrolysis or complex chemical change that destroys their original structure.
(2) Under acidic conditions, the sodium salt of 2,4-D, the sodium salt of MCPA and amitraz also decompose, reducing efficacy.
(3) Besides acidity and alkalinity, many pesticides cannot be mixed with products containing metal ions.
(4) Mixing dithiocarbamate fungicides or 2,4-D herbicides with copper formulations can form copper salts and reduce efficacy.
(5) Thiophanate-methyl and thiophanate can complex with copper ions and lose activity.
(6) Apart from copper formulations, other formulations containing heavy-metal ions such as iron, zinc, manganese and nickel must be mixed with particular caution.
(7) Mixing lime sulphur with Bordeaux mixture can produce harmful copper sulphide and also increase the content of soluble copper ions.
(8) Propanil, butachlor and similar products must not be mixed with organophosphate or carbamate insecticides; some chemical changes may cause crop injury.
● Pesticides with cross-resistance should not be mixed
For example, the fungicides carbendazim and thiophanate-methyl show cross-resistance. Mixing them not only fails to delay the development of resistance in the pathogen but actually accelerates it, so they must not be mixed.
● Biological pesticides must not be mixed with fungicides
Many pesticide fungicides are harmful to biological pesticides, so microbial pesticides must not be mixed with fungicides.
Source: Nongzi Daobao