It is quite common for rural producers (around 97% of them) to mix agricultural pesticides in the spray tank, as it becomes much more practical, not needing to re-enter the fields to apply agricultural pesticides, generating reduced costs, reduced time and less applicator exposure to chemicals.

Furthermore, in some cases the efficiency of products can even increase when used together, thus having a synergy effect. In the case of weed control, mixing herbicides is very common, especially when in the same area there is an infestation of monocotyledonous (narrow-leaf) and eudicot (broad-leaf) plants that are resistant and/or tolerant to herbicides (mainly glyphosate). An example of this is the use of 2,4-D associated with glyphosate to control plants such as pigweed (Amaranthus spp.) e buva (Conyza spp.), especially when they are at an advanced stage of development and/or due to difficulty in control when used only with glyphosate.

Is it permitted to mix pesticides?                                

Yes, it is permitted, however, it was only in 2018 that an agreement was signed between the Ministry of Agriculture, Livestock and Supply (MAPA) and the Federal Council of Engineering and Agronomy (Confea) that authorized agronomists to prescribe the application as a mixture of defensives. Previously, tank mixing was not recommended, but producers ended up making this mixture on their own, without formalized instructions. 

For the agronomist to be able to prescribe mixtures, it is necessary to have knowledge regarding the incompatibility of mixtures. The consequences can be quite negative when mixing with incompatible products. 

What's the problem with mixing herbicides?

Some pesticides, when combined, can cause inefficiency in weed control, thus causing an antagonism effect. This occurs for two reasons: physicochemical incompatibility and/or adverse biological effects (Ferreira et.al 1995). 

In the case of physical-chemical incompatibility, the main problems associated are difficulty in dissolving the products, excessive foam formation and formation of precipitates in the tank. 

Just like the mixture of herbicides, the addition of adjuvants to the mixture can also cause physical-chemical incompatibility, reduced product efficiency, as well as cases of phytotoxicity and loss of selectivity for some crops (Queiroz et al. 2008). Therefore, it is necessary to make a case-by-case assessment regarding the use of adjuvants. 

How to avoid the incompatibility problem?

Firstly, it is very important to make a test pre-mix with the same dilution used in the field to check for undesirable reactions, leaving it to rest for two hours. The negative point of this test is that it will not reveal biological incompatibilities.

To prepare the syrup, it is recommended that solid products (dispersible granules and wettable powders) be added first; and subsequently, the liquid formulations and finally the adjuvant. However, this information does not exempt you from observing the limitations regarding the use of mixed products, in order to avoid incompatibilities.

Figure 1. Visual analysis of physical-chemical compatibility of herbicide mixtures in the laboratory. A represents precipitate formation and B foam formation. Seropédica, RJ. Source: PDPA/UFRRJ.

From the visual analysis, it is possible to obtain a recommendation regarding the possibility of applying the mixture or not, according to the table below:

Table 1: stability of mixtures.

Source: Brazilian Center for Bioaeronautics (CBB), cited by Petter et al. (2012). Grade 1 means immediate separation of the compounds and grade 5 means perfect stability of the compounds.

In which mixtures does incompatibility occur?

The interaction between herbicides depends largely on the species, the herbicide itself and the dose used. In the literature there is some data regarding the incompatibility between these products, however more studies related to this subject still need to be carried out.

About 80% of antagonistic interactions occur in grasses (Zhang et al. 1995). In general, this occurs mainly when the graminicide is applied together with the latifolicides or shortly after. Bittergrass (narrow leaf), for example, ends up not being effectively controlled when the herbicide 2,4-D or cloransulam (latifolicides) is applied mixed with haloxyfop-p-methyl (graminicide), according to studies by Pinho et. Al 2017.

 Figure 2. Frontal view of bittergrass plants at the 3-4 tiller stage 35 days after application of treatments, subjected to the sequential herbicides haloxyfop followed by the herbicide latifolicida (A) and latifolicida followed by haloxyfop (B) at intervals 3, 6 and 12 days between applications (I3, I6 and I12). Seropédica, RJ. Source: PDPA/ UFRRJ.

Estudos de Lancaster et al, 2019, mostraram que herbicidas inibidores de ALS (imazethapyr e penoxsulam), FSII (propanil) e auxínicos (2,4-D) antagonizam a ação de quizalofope (inibidor da ACCase – graminicida). Os resultados indicaram que se deve ter muito cuidado em utilizar quizalofope em mistura. 

Contact herbicides (glufosinate, paraquat, among others) act quickly on leaf tissues and impair the absorption and translocation of systemic herbicides such as glyphosate (Bethke et al. 2013). 

PROTOX inhibitor herbicides (lactofen, sulfentrazone, etc.), which are contact and selectively control weeds, may present incompatibility when applied together with glyphosate.

The table below shows the main antagonistic interactions between herbicides. 

Table 2. Contextualization of antagonistic interactions between herbicides present in national and international publications. Source: (Challenges and Sustainability in Plant Management, 2019).

A mixture that has been widely used is that of 2,4-D with glyphosate, in pre-planting desiccation application. Several studies have evaluated whether there is an incompatibility reaction between these two active ingredients, and some of them, such as Takano et al, 2013, state that there may even be a synergistic effect, making the control more effective when applied together than when applied together. isolated form, especially when the weeds are in an advanced stage of development.

What's wrong with mixing 2,4-D with glyphosate?

Como falado anteriormente, não ocorre incompatibilidade biológica entre 2,4-D e glifosato, no entanto pode haver incompatibilidade física. O glifosato é um ácido, mas é aplicado nas lavouras na forma de sal, e o tipo de sal pode influenciar na formação de precipitados. Um estudo de Kleisinger et.al 2016 mostrou que quando o glifosato é aplicado na forma de sal de amônio de glifosato (como o produto comercial Roundup WG), ocorre a sedimentação imediata ao misturar com 2,4-D, e essa sedimentação não desaparece mesmo com agitação contínua (grau 1 – não recomendada a aplicação).

Já quando utilizado glifosato na forma de glifosato potássico (como o produto comercial Zapp Pro), não ocorre a sedimentação quando misturado com 2,4-D (grau 5 – pode ser realizada a aplicação). Vale ressaltar que o estudo foi conduzido para um volume de calda de aplicação de 50 L/ha e doses de 2,5 L/ha de glifosato e 1,25 L/ha de 2,4-D, ambos herbicidas concentrados solúveis. Todavia, mais pesquisas com essa abordagem devem ser realizadas, variando a dose e o volume de calda que se deseja aplicar

Figure 3. A. Mixture of glyphosate ammonium salt + 2,4-D acid amine. B. Mixture of monopotassium glyphosate + 2,4-D acid amine. Source: Agrositio

In any case, to have an accurate recommendation for applying the mixture of glyphosate with 2,4-D, it is very important to carry out the pre-mix test, since nowadays we have many commercial products on the market, and each one of them has its peculiarities that can influence the compatibility of mixtures.

Is mixing herbicides beneficial?

Mixing herbicides can be very interesting from an operational point of view, bringing operational time gains and cost reductions and in some cases it can even increase the efficiency of the products. However, close attention must be paid to the effects of incompatibility, as the application of incompatible products can lead to loss of weed control, which will result in poor management of the area, in addition to the great economic loss resulting from the purchase of products that will not bring results. or even generate physical incompatibility that will make the application unfeasible due to clogging of nozzles and filters, resulting in operational losses, requiring constant cleaning of the tips and filters or in more severe cases the need to discard the entire tank mixture.

References

FERREIRA, KL; BURTON, JD; COBLE, HD Base fisiológica para o antagonismo do fluazifop-P por DPXPE350. Weed Science., V. 43, n. 2, p. 184-191, 1995.

QUEIROZ, A. A.; MARTINS, J. A. S.; CUNHA, J. P. A. R. Adjuvantes e qualidade da água na aplicação de agrotóxicos. Bioscience Journal, v.24, n.4, p.8-19, 2008.

ZHANG, J.; A.S. HAMILL; S.E. WEAVER. Antagonism and synergism between herbicides: trends from previous studies. Weed Technology. v. 9, p. 86–90, 1995.

LEAL, J. F. L.; SOUZA, A. S. ; OLIVEIRA, G. F. P. B. ; RIBEIRO, S. R. S. ; CARVALHO, G. S. ; BORELLA, J. ; PINHO, C. F. Interação entre os herbicidas cloransulam-metílico e haloxifope-pmetílico no controle de buva. In: XXXI Congresso Brasileiro da Ciência das Plantas Daninhas, 2018, RIO DE JANEIRO. DESAFIOS E SUSTENTABILIDADE NO MANEJO DE PLANTAS DANINHAS, 2018.

LANCASTER, Z.D.; NORSWORTHY, J.K.; SCOTT, R.C. Residual Activity of ACCase-Inhibiting Herbicides on Monocot Crops and Weeds. Weed Technology, v.32, p.364 -370, 2018.

BETHKE, R. K.; MOLIN, W. T.; SPRAGUE, C.; PENNER, D. Evaluation of the interaction between glyphosate and glufosinate. Weed Science, v.61, n.1, p.41-47, 2013.

DE LA VEGA M. 2013. Tanque mistura em sprays com Atrazina, Glifosato e 2,4-D, em diferentes formulações. http://inta.gob.ar/documentos/herbicidas-mezclas-detanque/at_multi_download/ file/INTA%20-%20Herbicidas,%20mezclas%20de%20tanque.pdf