In 1945, Dr. Joseph L. Fennell expressed interest in developing hybrids for wine and fresh grapes from crosses between wild grape species from tropical forests and imported varieties, that could adapt to warm and humid climates, and eventually, be grown on a large scale (Fennell, 1945; Cruz, 1948). However, it was only in the 1970s that the first commercial plantations of European varieties were established in Costa Rica, located in Playa Panamá, Guanacaste, although the susceptibility of these varieties to Pierce’s disease (Xylella fastidiosa), as well as the lack of technical information, affected the evolution of the project (Sheng-Pin, 1988).

In 1985, a cooperative program between the Ministry of Agriculture and Livestock (MAG), the Nacional Learning Institute (INA), the Agrarian Development Institute (IDA) and the Republic of China’s Technical Agriculture Mission agreed to evaluate over 75 imported grapevine varieties, in order to select the ones that best adapted to the tropical climate (Sheng-Pin, 1988). On the path towards the establishment of the Ruby Seedless cultivar as the most promising one in that moment, the program also facilitated research, dissemination, training and technical assistance, which led to the creation of informative material on the agricultural management of the grapevine in Costa Rica (Lizano-Sáenz, 1992).

After the foundation of the Grape Farmer Association of Costa Rica in 1997, the plant material was tested in other areas in Costa Rica for several years, until in 2006, Republic of China Technical Agriculture Mission left the country. After that moment, several farmers retired from the activity and even sold their farms (Cordero-Pérez, 2022). Currently, grapevine growing activities have been recorded in five provinces: Alajuela, Cartago, Guanacaste, Puntarenas and San José (Cruz, 1948; Sheng-Pin, 1988; Pymes, El Financiero, 2015; Barquero, 2016; Fernández, 2016). However, the viticultural activity is not significant, and the 2021 National Agricultural Survey 2021 (INEC, 2022) does not report data on the area or varieties of grapevines planted in the country.

Despite the lack of official data on the current state of the crop, there are records of at least 9 farmers, located in the cantons of La Garita (Alajuela), Carrillo (Guanacaste), Acosta, Curridabat, Pérez Zeledón, Puriscal and Santa María de Dota (San José) (Figure 1). Out of these plantations, only those located in La Garita and Santa María de Dota are larger than 2 ha. The latter one is located at an altitude of over 2,000 m.a.s.l., the highest and largest in the country, with over 10 ha planted with different varieties of temperate-weather grapes for the production and export of wine. The remaining vineyards are located in warm-weather areas, at an altitude equal to or lower than 1,000 m.a.s.l.; this condition allows farmers to obtain two or more harvests every year.

On a commercial level, the vineyards in Acosta, La Garita and Santa María de Dota produce and own registered wine brands. In turn, the plantation located in Curridabat serves as a laboratory for the improvement of varieties that can be adapted to the tropical climate. The other plantations represent a secondary activity for farmers, who sell the grapes for fresh consumption and may occasionally produce craft wine.

Although these precedents suggest that there are possibilities of exploiting the winegrowing activity in different areas of the country, the lack of information on this crop limits the search for new areas with a potential for the activity. In addition, the alternatives for the chemical management of diseases are scarce, since according to the database of the State Phytosanitary Service (SFE, 2023), at the moment, only two fungicides are registered for use on grapevines: myclobutanil (triazole) and mancozeb (dithiocarbamate). Out of the two, only the latter is registered for use

Figure 1

against downy mildew. This situation restricts the profitability of the vineyards and the projection of small-scale companies to insert themselves in the commercial chain.

In Costa Rica, all grape farmers claim that under relatively high moisture levels and temperature, diseases appear that affect their grapevines, among which downy mildew is the most common, although nobody has estimated the losses it has caused. Other reported pathologies that affect to a lower extent include Pierce’s disease (Xylella fastidiosa), rust (Phakopsora euvitis) and downy mildew (Erysiphe necator), although the latter is only found in plantations in areas with warm weather. Likewise, there have been reports of damages caused by pests such as the grape root borer (Vitacea polistiformis), maybug (Phyllophaga spp.) and the fruit fly (Ceratitis capitata).

The majority of the area planted with grapevines in the world are done so with European varieties (V. vinifera), since yields are greater and their quality is considered superior (Sun et al., 2011; OIV, 2017; Teissedre, 2018). Nevertheless, the V. vinifera varieties are highly susceptible to diseases, including downy mildew, which is why it is considered a constant threat in wine-growing regions (Gessler et al., 2011; Yu et al., 2012; Wilcox et al., 2015; Ash, 2017).

The causal agent of downy mildew, P. viticola, is an obligate biotrophic parasite (Göker et al., 2007). The taxonomic classification locates it in the Chromista kingdom, phylum Oomycota, class Peronosporea, order Peronosporales and family Peronosporaceae (Index Fungorum, 2023). Although it is not a true fungus, ecologically and epidemiologically, it has a similar behavior (Kassemeyer et al., 2015). This organism is pathogenic for at least 28 species of Vitis, out of which V. vinifera and V. labrusca are the main hosts (Rouxel et al., 2014; CABI, 2021).

Plasmopara viticola is native to North America, where the wild and cultivated varieties of American origin (V. labrusca) display different degrees of resistance to the infection as a product of a longer period of coevolution with the pathogen (Bitsadze et al., 2014; Boso et al., 2014). By importing rootstock with resistance to phylloxera (Daktulosphaira vitifoliae) from the United States, P. viticola was introduced into southwestern France in the late 1870s, and from there, it spread to the rest of the continent, causing significant losses in yields, which extended throughout the first half of the 20th century (Gessler et al., 2011; Fontaine et al., 2021; Koledenkova et al., 2022).

Downy mildew is highly destructive in warm areas with abundant rainfalls, since moisture is the main cause of epidemics (Kennelly et al., 2007; Caffi et al., 2013; Koledenkova et al., 2022). When weather conditions are favorable and agronomic management is inappropriate, this disease can cause losses of up to 100% in production (Ash, 2017; Buonassisi et al., 2017). In addition to parasitizing the plant during the entire vegetative cycle, when the infection is severe, defoliation takes place, and as a consequence, the grapes lose their commercial and nutritional value (Jermini et al., 2010; Taylor, 2021). Due to a low accumulation of reserve carbohydrates, defoliation also causes losses in the yields of the next cycles (Matasci et al., 2008; Jackson, 2022).

In temperate regions, at the beginning of the spring, when temperatures are higher than 10 ºC, relative humidity reaches higher than 95 %, and the frequency of rainfalls increases, and the oospores, which are sexual survival structures and remain on the soil and the fallen leaves, germinate if a water layer remains for more than 24 h (CABI, 2021). Through a germinative tube, a macrosporangium is formed, which contains biflagellate zoospores that, dispersed by rainwater and wind, penetrate the live plant tissue, colonize, infect and reproduce asexually, which gives rise to a secondary infection cycle (Yin et al., 2017). This cycle may be completed in 5 days (Figure 2), depending on the weather conditions and the susceptibility of the host (Agrios, 2005; Kortekamp, 2005).

Figure 2

In polycyclic diseases such as downy mildew, both the oospores and the zoospores are involved in the origin of new infections. The former act as a primary inoculum and the latter, the secondary inoculum (Carisse, 2016; Maddalena et al., 2021; Massi et al., 2022). In the past it was thought that only the secondary inoculum contributed to the progress of epidemics, although evidence indicates that the oospores maintain their ability to germinate and cause infections for up to three months (Vercesi et al., 2010; Gessler et al., 2011; Rossi et al., 2013).

The zoospores are released from the sporangium when moisture levels in the air is high, and remain active for a few hours. Because they have no cell wall, their survival is determined by the presence of free water (Massi et al., 2022). After they reach susceptible tissue, these cells swim in the layer of water on the leaves until they reach the stomata, where they encyst, germinate and penetrate through them, by means of the action of enzymes that degrade the cell walls of the plant. In the sub-stomatal cavity, they form a vesicle, out of which hyphae branch out and colonize the cells of the mesophyll to produce haustoria (Fröbel and Zyprian, 2019). This structure absorbs the nutrients from the cells. Kassemeyer et al. (2015) indicate that sporulation takes place under temperatures above 13 ºC, a relative humidity of 95 % and at least 4 h of darkness, which completes the latent period of the disease.

The incubation period is also influenced by temperature. On average, symptoms take between 7 and 10 days after the beginning of the infection to appear, but it may extend up to 21 days (Ash, 2017). Additionally, this event varies depending on the organ of the plant that is infected and the ontogenic resistance expressed (Steimetz et al., 2012; Rossi et al., 2013; Buonassisi et al., 2017). This period is shorter between 20-25 ºC and in new leaves, and longer in temperatures below 12 ºC and in old leaves (CABI, 2021).

Downy mildew infections take place in all the photosynthetic tissues of the plant (Bitsadze et al., 2014; Fröbel et al., 2019). The initial symptoms appear on the upper surface of new leaves as oily chlorotic spots, which become brown as the lesions age (Figure 3A). On the other hand, in older leaves, the veins demarcate these lesions, forming small angular spots that grow and coalesce until they cover the entire tissue (Rossi et al., 2013; Taylor, 2021).

In the tendrils, petioles and inflorescences, infections cause tissues to thicken and roll up, followed by necrosis (Kassemeyer et al., 2015). Likewise, Koledenkova et al. (2022) mention that in sprouts and young grape bunches, the volume of the intercellular mycelia causes a deformity and the sinking of tissues, which quickly necrotize. Young bunches are highly susceptible to infections, but as they develop, resistance to the disease increases, due to the lenticels in the epicarp blocking the penetration of the hyphae (Carisse, 2016). Nevertheless, in mature bunches, the pedicel remains susceptible and the grapes can become infected from there (Gindro et al., 2022).

Sporangiophores are white and are produced in the abaxial side of leaves, around lesions and in the rest of the infected tissues (Figures 3B and 3C). After sporulation, the proportion of necrotic tissue increases, and eventually, the abscission of the affected organs takes place, along with the total defoliation of the plant (Taylor, 2021; Jackson, 2022).

Downey mildew management traditionally (Figur3 4) involves preventive agricultural practices, such as pruning and the use of stakes to promote ventilation and the reduction of moisture in the canopy, thus preventing the production of secondary infections (Agrios, 2005; Gessler et al., 2011). In the late 19th century, Bordeaux, France, a delay in the appearance of symptoms was observed after spraying grapevines with a mixture produced from copper sulfate and calcium hydroxide. The mixture became popular in other grape-growing regions of the world,

Figure 3

due to its strong adherence and persistence in plants, with the name of “Bordelais mixture.” Since then, copper salts have been used to prevent secondary infections in the spray programs, with variations in composition, dosage and application intervals depending on the pressure of the current inoculant (Lamichhane et al., 2018; Massi et al., 2021).

The scarcity of copper for agriculture during World War II led to the need to find new substances to fight downy mildew (Lamberth, 2019). In the 1970s, molecules

Figure 4

were created to control P. viticola with the ability to act upon this organism for more days, resist washing by rains, since they could be absorbed and translocated by the plant, and cure infections during its development (Massi et al., 2021). Nowadays, these fungicides, called “systemic” fungicides, are applied globally on a wide range of crops. However, in most winegrowing regions, P. viticola populations have been found that are resistant to diverse fungicide groups, and their resistance appeared as soon as these products started to be used (Wicks et al., 2005; Baudoin et al., 2008; Furuya et al., 2010; Lucas et al., 2015; Hall et al., 2017; Zhang et al., 2017; Toffolatti et al., 2018b; Campbell et al., 2020; Ghule et al., 2020; Santos et al., 2020b; Campbell et al., 2021; Massi et al., 2021).

To date there are 12 groups of fungicides available to control phytopathogenic oomycetes (Table 1), yet for the three most widely used-phenylamides (PAs), Quinone Outside Inhibitors (QoIs) and carboxylic acid amides (CAAs)-more cases of resistance have been reported for P. viticola and other downy mildew (Gisi and Sierotzki, 2015). Poor practices associated with the repeated application of

Table 1

FRAC Mode of Action	Group name	Chemical or biological group	Common name (active ingredient)
Nucleic acids metabolism	PAs (PhenylAmides)	Acylalanines	Metalaxyl, Mefenoxam, Benalaxyl, Kiralaxyl
		Oxazolidinones	Oxadixyl
Unknown	Cyanoacetamide-oxime	Cyanoacetamide-oxime	Cymoxanil
Cytoskeleton and motor proteins	Benzamides	Pyridinylmethyl-benzamides Toluamides	Fluopicolide Zoxamide
	Thiazole carboxamide	Ethylamino-thiazole-carboxamide	Ethaboxam
Cell wall biosynthesis	CAAs (Carboxylic Acid Amides)	Cinnamic acid amides	Dimethomorph, Flumorph
		Mandelic acid amides	Mandipropamid
		Valinamide carbamates	Iprovalicarb, Benthiavalicarb
Respiration	QoIs (Quinone outside Inhibitors)	Oxazolidine-diones	Famoxadone
		Imidazolinones	Fenamidone
		Methoxy-acrylates	Azoxystrobin
	QiIs (Quinone inside Inhibitors)	Cyano-imidazole	Cyazofamid
		Sulfamoyl-triazole	Amisulbrom
		2,6- dinitro-anilines	Fluazinam
	QoSIs (QoI, stigmetallin binding type)	Triazolo-pyrimidylamine	Ametoctradine
Multisite	Dithio-carbamates	Dithio-carbamates	Mancozeb
	Chloronitriles/Phthalonitriles	Chloronitriles	Chlorothalonil
	Inorganic	Inorganic	Copper (salts)
Plant defence induction	Phosphonates	Ethyl phosphonates	Fosetyl-Al

these fungicides accelerate this phenomenon and lead to the loss of effectiveness of commercial products. This situation not only hinders the progressive reduction of resistant populations, but also prevents the mitigation of the progress of the disease once it has been established (Hollomon, 2015).

Along with the economic cost implied by fighting against downy mildew, estimated by Taylor and Cook (2018) at USD $5 million per year, the resistance to fungicides causes the number of effective products for the management of this disease to decrease over time. Plasmopara viticola is described as an organism with a high risk of developing resistance, due to the high rate of asexual and sexual reproduction, as well as to the polycyclic behavior of epidemics (Toffolatti et al., 2011; Fungicide Resistance Action Committee [FRAC], 2019). The risk of resistance is higher for fungicides that act on a single biochemical site (Gisi and Sierotzki, 2008; Massi et al., 2021). However, multiple applications with these products are carried out every year, despite some studies concluding that curative control is not effective to contain the progress of the downy mildew epidemics (Hollomon, 2015; Massi et al., 2021; Poeydebat et al., 2022).

Astrategy recommended for the management of resistance consists of diversifying compounds with different mode of action in the applications. It is advised that the systemic action fungicides be combined with those that act on a multisite level, thus reducing the selection of resistant populations to the molecule with the highest risk (Brent and Hollomon, 2007; van den Bosch, 2014; Kassemeyer et al., 2015; Elderfield et al., 2018). Alongside this, the use of mixtures of fungicides encourage the potential synergism between molecules, which enhances a more prolonged residual effect (Gisi, 1996; van de Bosch, 2014).

The relative damage caused by this disease to viticulture activities exceeds that caused by other downy mildews in their respective hosts (Gisi and Sierotzki, 2008). This makes chemical control the most widely used management practice in the world to ensure optimal yields (Toffolatti et al., 2018a; Massi et al., 2021), positioning viticulture as one of the agricultural activities with the highest consumption of pesticides; in Europe alone, over 70 % of the fungicide market is dedicated to this crop (Muthmann and Nadin, 2007; Sargolzaei et al., 2020; Wingerter et al., 2021). This scenario underscores the discussion around the negative impact of pesticides in health and the environment, in such a way that modern practices must include more sustainable management practices (Romanazzi et al., 2016; Yu et al., 2022).

In order to reduce the chemical load on conventional systems, other approaches have arisen for the integrated management of this disease, in which greater importance has been given to the innate resistance of wild American Vitis species (V. labrusca, V. rotundifolia, V. rupestris, V. riparia amd V. cinerea), as well as Asian ones (V. amurensis, V. piasezkii and V. coignetiae), which display partial or total resistance to the disease, conferred by multiple resistance genes (R) (Merdinoglu et al., 2018; Koledenkova et al., 2022). Although these varieties are not planted for the wine market, the existence of this germplasm is a valuable resource for breeding programs that focus on generating materials with resistant to downy mildew and other biotic and abiotic stress factors (Moreira et al., 2011; Yu et al., 2012; Toffolatti et al., 2016; Buonassisi et al., 2017).

The development of varieties with genetic resistance is the most sustainable alternative to control grapevine diseases and reduce the use of pesticides (Mundt, 2014; Zini et al., 2019; Fröbel et al., 2019). However, conventional breeding techniques are costly and the observation of results may take up to 30 years (Eibach and Töpfer, 2015; Sargolzaei et al., 2020).

The need to introduce R genes from wild species into cultivated grapevines has led, since the early 20th century, to the development and registration of thousands of hybrids with a greater resistance to the disease (Pacifico et al., 2013). However, during hybridization, wild parents segregate characteristics that modify the chemical properties of the grapes, which translates into a low-quality wine. Due to this, most of these hybrids have been discarded from the market (Eibach and Töpfer, 2015; Pertot et al., 2017; Toffolatti et al., 2018a; Foria et al., 2022).

To overcome the difficulties related to the duration of conventional breeding and to the value of wines made from hybrids, the use of molecular markers has helped detect the main QTLs (quantitative trait loci) of wild plants associated with the different levels of resistance to downy mildew, which makes it easier to evaluate the genotypes harboring the R genes (Zyprian et al., 2016; Merdinolgu et al., 2018; Sargolzaei et al., 2020). By mapping the QTLs that intervene to a greater and lesser degree to resistance, significant associations can be found between molecular markers and the phenotypes resistant to this disease (Divilov et al., 2018; Possamai and Wiedemann-Merdinoglu, 2022). This knowledge is the basis for the marker- assisted selection, which has helped reduce the breeding process considerably, since the candidate varieties that not only combine diverse resistance factors, but also important agronomic characteristics such as quality and yield can be identified, as far back as the seedling stage (Fischer et al., 2004; Eibach and Töpfer, 2015; Merdinolgu et al., 2018; Fu et al., 2020).

Current agronomic practices for the integrated management of this disease consider the relation between the weather variables and the progress of epidemics, in order to identify between climate variables and other critical moments that require applications (Caffi et al., 2011; Gessler et al., 2011). By recording the temperature, relative moisture, rainfalls and leaf wetting, prediction models can be created for these epidemics. These predictions are integrated into alert systems to help make decisions during the moments of greatest susceptibility, with the aim of optimizing the effect of the applications to the fullest (Madden et al., 2000; Dalla Marta et al., 2005; Rossi et al., 2013; Brischetto et al., 2021).

Regarding cultural management strategies, it is advisable to control moisture, both at soil and canopy levels (Thind et al., 2004; Mian et al., 2021), use clean machinery and vegetative material, plant at an optimal density, and maintain a balanced level of nitrogen (Taylor, 2021). In agroecological and organic systems, as an alternative to copper, inducers are used to promote the activation of the defense system of the plant, prior to infection events. The preventive application of these substances helps reduce the use of fungicides, since it takes advantage of the early induction of resistance responses (Guerreiro et al., 2016; Jacquens et al., 2022).

Among the most widely studied inducers, it has been proven that chitosan, when applied preventively, reduces severity in grapevine leaves at greenhouse (Aziz et al., 2006; Llamazares De Miguel et al., 2022) and field levels (Vitalini et al., 2020; Taibi et al., 2022; Mian et al., 2023), through an increase in the accumulation of salicylic acid and phytoalexins in tissues, as well as an overexpression of genes for the synthesis of pathogenesis-related proteins (PR) (Aziz et al., 2006; Inchaya et al., 2013; Mian et al., 2023). On the other hand, Romanazzi et al. (2021) and Vitalini et al. (2020) determined that different individual chitosan formulations, or mixed with copper, help reduce the incidence and severity in leaves and grape bunches against high and low pressures of the disease in commercial grapevines.

Similar effects to those produced with chitosan have been reported with the use of laminarin, a glucan derived from the algae Laminaria digitata. The application of this substance promotes the expression of defense genes and PR proteins (Aziz et al., 2003; Gauthier et al., 2014). Likewise, its efficiency for the control of downy mildew in the greenhouse and field has been proven in individual applications or combined with copper (Paris et al., 2016; Romanazzi et al., 2016; Taibi et al., 2023).

The induction of these resistance mechanisms has also been found when using β- aminobutyric acid (BABA), whose effect on the disease has been observed in controlled environments (Hamiduzzaman et al., 2005; Slaughter et al., 2008; Dagostin et al., 2011) and on the field (Reuveni et al., 2001), and benzothiadiazole (BTH), a synthetic compound, analogous to salicylic acid, which favors the synthesis of phytoalexins (Dufour et al., 2012; Burdziej et al., 2021) and helps reduce the incidence and severity of the disease in greenhouse conditions (Dagostin et al., 2006; Perazzolli et al., 2008; Harm et al., 2011). However, only BTH exists as a commercial product (Bion® 50 WG, Syngenta).

The action of endophytic fungi as potential biocontrol agents has also gained greater importance. Individuals belonging to Acremonium sp., A persicinum, A. sclerotigenum, A. byssoides y Alternaria alternata have been identified, and their metabolites in in vitro conditions display anti-germinative activity on the sporangia of P. viticola (Assante et al., 2005; Musetti et al., 2006; Arnone et al., 2008; Lo Piccolo et al., 2015). On the other hand, through mechanisms such as hyperparasitism and enzymatic lysis, Epicoccum nigrum and Fusarium proliferatum, respectively, have displayed control over P. viticola, in vitro (Bakshi et al., 2001; Kortekamp, 1997; Shen et al., 2017).

Likewise, endophytic bacterial strains such as Bacillus subtilis, B. pumilus, B. altitudinis, Ochrobactrum sp. and Pseudomonas fluorescens have been effective in reducing the impact of downy mildew in the greenhouse and the field (Furuya et al., 2011; Zhang et al., 2017; Lakkis et al., 2019; Zang et al., 2020; Zeng et al., 2021). Other non-endophytic organisms on which there have been reports of control over P. viticola include Trichoderma koningiopsis and commercial formulations with T. harzianum T9, which also have the effect of resistance induction (Perazzolli et al., 2008; Kamble et al., 2021; Palmieri et al., 2021; Küpper et al., 2022). In another study, Bolzonello et al. (2023) found that, when preventively using synthetic analogs of secondary metabolites of Trichoderma spp. on leaf discs, P. viticola cells display membrane rupture and cytoplasmic granulation, which represented a similar level of protection to a copper-based fungicide.

Regarding bacteria, Lysobacter capsici, AZ78, Streptomyces atratus PY-1 and S. viridosporus HH1 were established as reducers of the severity of the disease (Puopolo et al., 2014; Liang et al., 2016; El-Sharwaky et al., 2018; Brescia et al., 2021; Markellou et al., 2022). On the other hand, Pozzebon and Duso (2008) recorded that the mites Amblyseius andersoni and Typhlodromus pyri feed off P. viticola mycelia and spores, which makes them candidates for biological control.

Out of all the phytosanitary problems of the vineyards in Costa Rica, downy mildew is the most limiting, causing losses that, although not estimated, have been observed in different magnitudes. For their management, winegrowers carry out suckering, constant trimming and apply copper salts and mancozeb as a prevention measure, since chemical control is restricted to a single active ingredient. Likewise, when the presence of inoculum is high, the most affected leaves are cleansed and removed from the plantation.

In the case of farmers that have materials that descend from V. labrusca in their vineyards, downy mildew does not represent a significant problem. Among them, the hybrid Isabella (V. labrusca × V. vinifera) is the most common in warm climate vineyards, both for its tolerance to the disease and for being the one that has adapted best to tropical conditions. Since the activity in Costa Rica is incipient, no molecular breeding techniques have been implemented to develop materials that resist downy mildew, nor have there been reports on the use of effective biological controllers of this pathogen.

With the exception of the hybrid Isabella, in most of the varieties planted in the country, this disease generates losses in productivity. Among them, the variety Syrah is highly susceptible, although it has also stood out as one of the temperate climate cultivars with the highest potential for wine production in tropical areas (Camargo et al., 2011; Tonietto and Pereira, 2011; Commins et al., 2012; Wurz et al., 2017). This variety is planted only in the most technified vineyard in the country, located in Dota, and it is considered high-quality for the production of wine. For all these reasons, it is important to elucidate management strategies that reduce the impact of epidemics.

An obstacle for the production of Syrah in Dota is the delay in growth, in comparison with the phenological cycle observed in temperate regions (Serrano- Segura, 2020, personal communication). This condition causes the vegetative period to be more prolonged, and therefore, for the pathogen to reproduce for longer. Alongside this, the climatic conditions of the place allow for the fulfillment of the 3-10 rule for primary infections of grapevine downy mildew, according to Rossi et al. (2013): 10 cm of leaf tissue, at least 10 mm of rain in the last 48 h, and more than 10 ºC.

As part of the agronomic management for Syrah, after harvesting, the plants remain with little maintenance while the leaves translocate the remaining nutrients to the trunk, so they accumulate the necessary reserves for the budding of the following cycle, after which a high dose of ammonium nitrate is applied as a burner. Later, the productive branches of the previous period are trimmed to give rise to the productive offspring of the following cycle. Next, cold compensation is applied to break the dormancy of the lateral buds which, approximately one year later, will bud and begin a new crop cycle, as well as a pathogen cycle.

In the Dota vineyard, a wide variety of contact, translaminar and systemic fungicides have been evaluated to determine their efficiency against the disease. However, the efficiency of some active ingredients has decreased with time. Copper- based contact products have been observed to be ineffective in the rainy seasons, whereas some tested systemic fungicides have caused toxicity at commercial or lower doses. On the other hand, products formulated with B. subtilis have not given adequate results, either, according to visual estimations in the progress of the epidemic.

The lack of new permitted active ingredients in Costa Rica for the management of this disease is an obstacle, not only for the production of Syrah, but also for the other varieties planted in Dota and the rest of the country. Currently, out of the 25 available active ingredients in the world for the control of phytopathogenic oomycetes (Table 1), in Costa Rica, only mancozeb is permitted for use against the grapevine downy mildew. Although this fungicide is used in all vineyard-producing areas, except for the European Union (Debelder, 2020), its individual use in an spray program is not enough against epidemics in Dota, where, additionally, climate conditions favor the accelerated development of the disease. For these reasons, it is appropriate to determine the effect of new molecules and mixtures that may eventually be registered for use on grapevines.

During the period of 2019 and 2020, the best result in a vineyard, in terms of yield, against downy mildew in the Syrah variety was obtained by applying a cyazofamid-based fungicide. Nevertheless, this molecule is only registered for the control of Phytophthora infestans in potato and tomato, and Pseudoperonospora cubensis in cantaloupe and watermelon, two phytopathogenic oomycetes of great economic importance for agriculture.

In an investigation carried during the 2020-2021 production cycle (data not published), both cyazofamid and the mixture of cymoxanil + fosetyl-Al + mancozeb were determined to be effective in reducing the impact of the disease. These results show the importance of performing biological efficacy tests for molecules that have not been evaluated in this pathosystem, which provide an approach towards new registrations, with the aim of continuing to search for strategies that can help establish an integrated and sustainable management of the activity.