MAY 2022

APPLICATION OF TRIAZOLES FORCONTROL OF COFFEE LEAF RUST(HEMILEIA VASTATRIX)
Technical Paper

The Rainforest Alliance is creating a more sustainable
world by using social and market forces to protect natureand improve the lives of farmers and forest communities.

1Introduction

most effective protectant fungicides, and triazoles are
the most common systemic fungicides. Triazoles can beused alone or in mixtures with Qo Inhibitors (strobilurin)
and are applied either on the leaves or in the soil (Zambolim 2016).

Coffee leaf rust, caused by the fungus Hemileia vastatrix, is the main disease affecting coffee plants globally(Talhinhas et al. 2017). This disease is found in all regions
where arabica (Coffea arabica) and robusta (C. canephora) coffee are grown and negatively impacts coffee plant health and productivity. In Latin America, coffee
leaf rust has caused yield reductions of up to 50% in Brazil, 30% in Colombia, and 16% in Central America (Avelinoet al. 2015; Zambolim 2016).

In Latin America, different active ingredients from thetriazole family are used to control leaf rust, dependingon the country. These include cyproconazole, difenoconazole, epoxiconazole, metconazole, tebuconazole,tetraconazole, triadimenol, propiconazole, and others.
Many triazoles are toxic to mammals, including humans,and to birds, insects, fish, and other organisms. Of triazoles commonly used on coffee farms, cyproconazole,epoxiconazole, propiconazole, and triadimenol are classified as Highly Hazardous Pesticides by the FAO/WHO
and are included in the Rainforest Alliance’s list of prohibited substances, meaning that their use is banned onRainforest Alliance Certified coffee farms.

Leaf rust can be sustainably managed by using resistant coffee cultivars, implementing early warning systems, and designing crop management systems that
account for threats posed by climate change and otherenvironmental conditions (Belan et al. 2020; de Resende
et al. 2021; Sera et al. 2022). Nonetheless, chemical control consisting of protectant and systemic fungicides iswidely used to prevent and control coffee leaf rust, despite their potential negative impact on human and environmental health. Copper-based compounds are theThe purpose of this technical paper is to explain Rainforest Alliance’s position on triazole use and summarize thescientific literature underpinning that position.

A coffee plant affected by coffee leaf rust. Photo: Giuseppe Cipriani

2

EXCEPTIONAL USES

the disease reached an incidence level of up to 30% by
the early summer, when climate conditions favour rustprogression. At this point, foliar treatments were needed
to control progress of the disease, suggesting that soil
applications on their own are not sufficient (de Souza etal. 2011). Similarly, Honorato et al. (2015) found that spraying C. arabica leaves with systemic fungicide controlled
rust as effectively as strategies that combined soil andfoliar applications, suggesting that the foliar strategy ismore cost-effective, since it involves fewer applications
and less active ingredient overall.

In exceptional circumstances, the Rainforest Alliancegrants producers limited authorization to temporarily
use prohibited pesticides. Exceptions are developed forspecific crops, countries, and pests in line with Rainforest
Alliance’s Integrated Pest Management (IPM) strategy
in response to exceptional use requests received fromproducers. Exceptions are granted after careful review
and are based on a determination of whether farms arereliant on a given pesticide to remain economically viable. These temporary authorizations are intended togive producers time to transition away from reliance on
hazardous substances while specifying risk mitigation
measures that must be in place in the meantime. Moreinformation is available on our page on the Rainforest Alliance’s Exceptional Use Policy (EUP).

A separate study in Brazil found that foliar application of
epoxiconazole was more effective than soil drench withflutriafol, as foliar applications could be tailored to disease incidence (Belan et al. 2015). These two strategies– foliar and soil application – were tested on 13 C. canephora clones and in some cases rust incidence stayed
below a 5% threshold for the entire growing season in theabsence of treatment, suggesting that treatment withfungicide is not always needed and should be selectedbased on the presence of disease (Belan et al. 2015). In
general, studies show that strategies where fungicide isapplied based on a fixed calendar are not as effective orefficient as adaptive strategies based on rust incidence
or forecast systems (Capucho et al. 2013; Hinnah et al.
2020). For example, soil-based fungicide strategies often
involve applying triazoles to coffee plots at the beginningof the rainy season, or to coffee seedlings in nurseries.
As a result, these strategies are not tailored to current
rust outbreaks or incidence levels, which can lead toover-application (additional foliar sprays needed) andlower the cost-effectiveness of fungicide treatments.

Regarding triazole use, exceptions have been granted
for foliar applications of cyproconazole until 2024 andfor epoxiconazole until 2023 for controlling leaf rust in theLatin American coffee sector. However, soil applicationsof triazoles listed in the EUP, including commercial formulations of cyproconazole + thiamethoxam, are prohibited under clause 2k, as explained below.

RAINFOREST ALLIANCE POSITION ONTRIAZOLESThe Rainforest Alliance discourages the use of triazoles
via soil application, as research suggests that foliar application is more effective for controlling coffee leaf rust.
Foliar application methods also reduce the risk of contamination to soil and aquatic ecosystems by minimizing runoff and leaching.
Additionally, clause 2k of Rainforest Alliance’s Exceptional Use Policy (EUP) prohibits soil application of triazoles
listed in the EUP, since these substances must be usedin the most precise and efficient way possible. As detailed below, research suggests that foliar applicationsof triazoles are more efficient and better protect environmental health.

EVIDENCE ON TRIAZOLE STRATEGIES: SOIL VS.
FOLIAR APPLICATIONS
Efficacy for coffee leaf rust (Hemileiavastatrix)

Multiple studies suggest that triazoles are less effective in controlling coffee leaf rust when applied via soil
drench, compared to foliar application. Research from
Costa Rica has revealed that three times as much triazole active ingredient is required in soil applications,and that soil applications are less effective than foliar
applications against diseases including leaf rust andOjo de Gallo (Mycena citricolor; M. Barquero-CICAFE,
personal communication, March 2, 2022). A five-year
study in Brazil also found that foliar application with epoxiconazole was more effective at controlling rust in C.
arabica compared to systemic fungicides applied to thesoil at the beginning of the rainy season (de Souza et al.
2011). The study showed that, although soil applications
were effective at keeping rust under control until March,

Foliar application of agrochemicals.

3Effect on productivity

Leaching of triazoles into soil and runoff into waterbodies can have serious negative impacts on soil-dwelling
and aquatic organisms. Soil application of triazoles canalso impact human health if these substances maketheir way into waterbodies that are used for drinking orwashing, as many triazole fungicides are highly toxic tomammals, including humans.
For example, cyproconazole and thiamethoxam arehighly soluble in water and are persistent in soil. Thesechemicals also have a high potential to leach into groundand surface water and are moderately to highly toxic tomammals, birds, insects including earthworms and pollinators, and aquatic organisms including fish, invertebrates, crustaceans, and aquatic plants (PPDB 2022).

Although the use of fungicides can boost coffee productivity, studies do not find a productivity benefit of soil
application of triazoles over foliar application. Researchfrom Costa Rica and Brazil has found no difference inproductivity between coffee plants treated with foliarand soil applications of triazoles (M. Barquero-CICAFE,
personal communication, March 2, 2022; de Souza et al.
2011). In fact, one study from Brazil found that foliar applications alone resulted in marginally higher yields forC. arabica than a strategy that combined soil and foliar
applications (Honorato et al. 2015).
There is some evidence that soil application of triazoles
can cause a “tonic effect” in coffee plants, which is characterized by thickening leaf tissue, increased foliage, andgreener leaf tone (Silva et al. 2018; Moura et al. 2013). Although this effect can give the impression of improved
plant health, studies show that the tonic effect can ultimately cause metabolic stress in coffee plants, affecting
longer term growth and plant vigor, with potential negative impacts on productivity (Martins et al. 2011; Carvalho
et al. 1997).

Other popular triazoles, including flutriafol, triadimenol,and propiconazole are also water soluble and therefore
readily make their way into groundwater and nearby
aquatic ecosystems with moderate toxicity to mammals, birds, insects, and aquatic organisms (PPDB 2022).
A study from Brazil demonstrated these impacts in thefield: of 38 active ingredients commonly used in coffee(across insecticides, herbicides, and fungicides), flutriafol, epoxiconazole, and cyproconazole were the most
likely to leach into soil and were found in the greatest
concentrations in groundwater (de Queiroz et al. 2018).
Further, flutriafol and epoxiconazole were found in concentrations that were toxic to local aquatic ecosystems.
Based on these findings, the authors of this study recommend that applications of these triazoles be avoided incoffee plantations that are close to surface or groundwater, due to the risk of toxic contamination (de Queirozet al. 2018).

The negative metabolic impact of triazoles applied via
soil may be especially pronounced if fungicides are applied to young plants in the nursery or field, or to soil thatis not nutritionally balanced or lacking proper moisture(Martins et al. 2011). For example, in a controlled greenhouse experiment, soil applications of cyproconazole+ thiamethoxam significantly reduced vigor in C. canephora seedlings compared to a control where nofungicide was applied, suggesting a phytotoxic effect oftriazoles applied via soil (Martins et al. 2011). A separate
study found that an increase in the concentration of triadimenol applied to the soil was associated with a decrease in the size of C. arabica plant sprouts (Carvalhoet al. 1997).

Conclusion
Given their potentially toxic impacts, triazole fungicides
should be applied in a manner that maximizes effectiveness while minimizing environmental contamination. Evidence shows that foliar application of triazoles is more
efficient and effective than soil application and reduces
negative environmental impacts. The Rainforest Alliance
therefore discourages soil applications of triazoles generally and does not allow soil applications of triazoles
listed in the EUP due to their heightened toxicity. Throughthe 2020 Standard, supporting guidance, training initiatives, and the EUP, the Rainforest Alliance provides a suiteof resources and services to help producers transition
away from reliance on toxic triazoles to treat coffee leafrust.

Environmental impact
Many triazoles that are commonly used to control coffee
leaf rust are known to have negative impacts on humanand environmental health. These impacts can be exacerbated when triazoles are directly applied to soil due
to runoff and leaching. Compared to soil applications,foliar applications are more precise since they can betargeted to specific leaf rust outbreaks. The soil application strategy therefore generally involves more active
ingredient overall (M. Barquero-CICAFE, personal communication, March 2, 2022) and results in direct contactof triazoles with soil, surface water and groundwater.

4

REFERENCES

De Queiroz, V., Azevedo, M., Quadros, I., Costa, A., Alves, A.,Santos, G., Juvanhol, R., Santos, A., Arthur de Almeida Telles, L. (2018). Environmental risk assessment
for sustainable pesticide use in coffee production.
Journal of Contaminant Hydrology. 219. https://doi.
org/10.1016/j.jconhyd.2018.08.008

Avelino J., Cristancho M., Georgiou S., Imbach P., AguilarL., Bornemann G., Läderach P., Anzueto F., Hruska A.J.,
Morales C. (2015). The coffee rust crises in Colombiaand Central America (2008–2013): impacts, plausible causes and proposed solutions. Food Security. 7:
303–321.

Hinnah, F.D., Sentelhas, P.C., Patricio, F.R.A., Paiva, R.N.,
Parenti, M.V. (2020). Performance of a weather-based
forecast system for chemical control of coffee leafrust. Crop Protection. 137. https://doi.org/10.1016/j.cropro.2020.105225

Belan L.L., Jesus-Junior W.C., Souza A.F., Zambolim L.,
Tomaz M.A., Alves F.R., Ferrão M.A.G., Amaral J.F.T.
(2015). Monitoring of leaf rust in conilon coffee clones
to improve fungicide use. Australasian Plant Pathology. 44: 5–12.

Honorato J., Zambolim, L., Lopes, U., Lopes, U., Duarte, H.
(2015). DMI and QoI fungicides for the control of coffee leaf rust. Australasian Plant Pathology. 44. https://doi.org/10.1007/s13313-015-0373-4.

Belan, L.L., de Jesus, W.C. Jr., de Souza, A.F., Zambolim, L.,
Filho, J.C., Barbosa, D.H.S.G., Moraes, W.B. (2020). Management of coffee leaf rust in Coffea canephora
based on disease monitoring reduces fungicide useand management cost. European Journal of Plant
Pathology. 156: 683-694.

Martins, L.D., Rodrigues, W.N., Tomaz, M.A., de Souza, A. F.,
de Jesus, W.C. Jr., Donatelli, E.J. Jr. (2011). Loss of vigor
in conilon coffee seedlings due to the application ofgranular fungicide for soil. Nucleus. 8(2): 97-104.
PPDB, (Pesticide Properties DataBase). (2022). A to Z Listof Active Ingredients. [En línea]. Disponible en: Pesticide Properties Database (herts.ac.uk). Consultation
date: March 15th, 2022.

Carvalho, G.R., Pasqual, M., Antunes, L.E.C., da Silva, A.T.,
Scarante, M.J. (1997). Efeito do Triadimenol d Benzilaminopurina no Desenvolvimento de Brotos in Vitro doCafeeiro cv. Catuai. UNIMAR. 19(3): 767-775.

Talhinhas,P., Batista, D., Diniz, I., Vieira, A., Silva, D.N., Loureiro, A., Tavares, S., Pereira, A.P., Aziheira, H.G., Guerra-Guimaraes, L., Varzea, V., do Ceu Silva, M. (2017).
The coffee leaf rust pathogen Hemileia vastatrix: one
and a half centuries around the tropics. MolecularPlant Pathology. 18(8): 1039-1051.

De Resende, M.L.V., Pozza, E.A., Reichel, T., Botelho, D.M.S.
(2021). Strategies for coffee leaf rust management inorganic crop systems. Agronomy. 11. doi.org/10.3390/agronomy11091865
De Souza, A., Zambolim, L., Júnior, V. Cecon, P. (2011).
Chemical approaches to manage coffee leaf rust indrip irrigated trees. Australasian Plant Pathology. 40:
293-300.

Zambolim, L. 2016. Current status and management ofcoffee leaf rust in Brazil. Tropical Plant Pathology. 41:
1–8.

5

rainforest-alliance.org
email: info@ra.org

6