Analysis of Climatic Risk Favorability of Grapevine Fungal Disease Occurrence for Santa Teresa , Espírito Santo State , Brazil

The State of Espírito Santo, Brazil, has micro-regions with different climatic and soil conditions, which promote grapevine cultivation vine in several municipalities. However, the grape production process is strongly threatened by foliar fungal diseases, and its control increases the cost of production significantly. In turn, the use of models of prediction of disease occurrence allows the identification of regions with climatic risk potential for grapevine. Hence, the objective of this work was to analyze the agro-climatic favorability of climatic risk for occurrence of fungal diseases of downy mildew (Plasmopara viticola) and Botrytis cinerea on the grapevine for the municipality of Santa Teresa, in the state of Espírito Santo. Predictive models of favorability of downy mildew and B. cinerea were used. The number of sprayings was determined by the calendar system and by the rainfall system, according to the length of the cycle. Therefore, a series of meteorological data from 2007 to 2016 was used. The results showed that the frequency of days with low risk of mildew was 2%, medium risk 5%, high risk 93%. For B. cinerea, these values were 32%, 68%, and 0%, with low, medium and high risk, respectively. The number of required sprayings, according to the weather conditions, was lower than the number of sprayings recommended by the calendar system. The relationship between the risk of occurrence of the evaluated diseases showed a higher agro-meteorological favorability of occurrence of mildew in relation to B. cinerea.


Introduction
The winemaking chain is potentially relevant due to its economic and social importance, generating labor and income in the country and the agro-industrial sector for the Country. The Brazilian winegrowing occupies an area of approximately 77,700 ha, with annual production varying between 1,300 and 1,400 thousand tons (Mello, 2015). In 2016, approximately 60% of the total production was commercialized for fresh consumption and 40% destined to the processing of wines and grape juice (Mello, 2015).
The State of Espírito Santo has in its microregions different conditions of climate and soil, which facilitates the production of the grapevine in several municipalities. Due to the pioneering spirit, tradition and dedication of the farmers, the municipality of Santa Teresa stand out as the largest producer of grapes and wine, with an expressive planted area (53 ha), knowledge and technology transfer for all the state (Incaper, 2016).
Grape crop is affected by several factors that depreciate its yield, where the occurrence of fungal diseases (Sonego et al., 2005) excels. According to Tonietto et al. (2012), downy mildew (Plasmopara viticola) and bunch rot (Botrytis cinerea) stand out among the major diseases that affect grapevines in the Espirito Santo     (1) The model described by Broome et al. (1995) for B. cinerea was selected. This model identifies periods of infection in grape berries according to leaf wetness duration and in average temperature over wetness events. This model is represented by Equation 2. (2) Where, II = infection index; LWD = leaf wetness duration, in hours; T = temperature over the wetness period, in °C; In[Y/(1 -Y)]= disease incidence logit; and Y = infected fruit proportion.
The LWD was estimated from the number of hours in which the humidity presented NRH ≥ 90. The threshold adopted is considered a common value in the literature (Sentelhas et al., 2004). The temperature over the wetness period was computed when the number of hours of relative humidity reached values ≥ 90.
For the potential risk of occurrence of fungal diseases in grapevines, the days with high, medium and low infection risk were analyzed. For mildew, infection efficiency (IF) was characterized by zero condition when the percentage is equal to zero (0%) and the highest infection efficiency corresponding to a value of one hundred percent (100%). Also, for mildew, in the frequency analyzes, it was characterized by infection efficiency (IE) values as follows: IE less than 3.5% corresponds to a low risk of infection; IE between 3.5 and 50% corresponds to the average risk of infection; and IE greater than 50% corresponds to the high risk of infection. For B. cinerea, the following risk classes were considered: Infection index less than 0 corresponds to no risk of infection; between 0.0 and 0.50, low risk; between 0.50 and 1.00, medium risk; and when the index is greater than 1.0, it corresponds to a high risk of infection.
The climatic risk (CR) of occurrence of fungal diseases in the grapevine, defined as the ratio between the number of sprayings required due to the occurrence of rainfall (NSrain) and the maximum number of possible sprays based on the calendar, considering that a spray is carried out every seven days (NScalendar) as a function of cycle length: pruning-harvest, expressed in percentage was estimated according to García (2005) and Bardin et al. (2010).
( 3) Where, CR = climatic risk; NPrain = number of required sprayings due to the rainfall occurrence; NP calendar = maximum number of possible sprays based on the calendar, considering that a spray is carried out every seven days.
Daily rainfall values for 10-year meteorological data series (2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016) were used to calculate the CR. The number of sprays required to control fungal diseases in the vine was determined according to Pedro Júnior et al. (1999), using the rainfall system for a recommendation of the application of fungicides. The applications are made after the occurrence of periods that total 20 mm of rain, respecting the lack of seven days of the commercial product.
Regarding data analyses of the annual and average values of CR, this variable was classified into four classes according to the following intervals, proposed by Shimano and Sentelhas, (2013): Low < 20% (L); Moderate, between 21 and 40% (Mo); High, between 41 and 60% (H); and Very High > 60% (VH). All calculations, statistical analysis, and graph confection were elaborated using Excel electronic spreadsheet and open source program R (R Core Team, 2016).

Results and Discussion
The favorable prevalence of mildew was characterized by the low average frequencies of the occurrence of days with high, medium and low infection risk between 2007 and 2016, for Santa Teresa, state of Espírito Santo, as shown in Figure 3. It was observed that frequency of days with low risk was 2%, medium risk 5%, and high risk 93%, evidencing that the Santa Teresa region presents highly favorable climatic conditions for the occurrence of mildew, therefore, requiring more efficient control measures. These high-risk results were superior to those found by Alves et al. (2015), in the region of Santana do Livramento, state of Rio Grande do Sul, which verified frequency of days with low risk of 23%, medium risk, 45%, and high risk, 32% for mildew of the vine. According to Angelotti et al. (2017), the area that favors the occurrence of grape mildew in Brazil is around 90%, with 1% less favorable area and 5% unfavorable area.      Vol. 11, No. 14;2019 The climatic risk for the occurrence of the diseases caused by mildew and B. cinerea shown in this study also allows observing that in all the years analyzed, the number of required sprayings, according to the meteorological conditions, was smaller than the number of sprayings recommended by the calendar system. This demonstrates that streamlining the control of fungal diseases is necessary to reduce the risks of contamination of the environment, of the producers and the final consumer. These results corroborate with those obtained by Shimano and Sentelhas (2013) when determining the climatic risk of occurrence of fungal diseases in different producing regions of the South and Southeast of Brazil, using the same model of spraying prediction based on the occurrence of rainfall. The authors demonstrated that the occurrence risk of these diseases varies according to the climate and that the monitoring of the meteorological conditions can help to the rational recommendation of sprayings for the control of fungal diseases in the Vitis labrusca grapevine. Figure 7 shows the year-on-year variation in climatic risk of occurrence of mildew and B. cinerea for grapevine in Santa Teresa, Espírito Santo, Brazil. A gradual increase in the CR of B. Cinerea was found in comparison to the mildew, with a substantial increase also in the year-on-year variability. While the mildew CR remains classified as low, moderate and high, for B. cinerea, RC ranges from moderate to high.

Conclusion
The favorability analyses of mildew and B. cinerea occurrence showed a frequency of days with a high risk of 93% and medium risk 68%, respectively, for the region of Santa Teresa, Espírito Santo, where the occurrence of mildew is more favorable.
The results of the analyses of the days with a low, medium and high risk of infection are primarily associated with regard to the LWD values. Lower values of LWD correspond to higher frequencies of days of low and medium risk of infection of diseases, higher values of LWD correspond to higher frequencies of days of the high risk of infection of diseases.
Higher occurrences of climatic risks of mildew and B. cinerea were found for grape growing in years with the most prolonged wetness periods.
The rainier years showed higher values of climatic risk. Also, for mildew, it remains in the majority of evaluated years classified as moderate and high, whereas for B. cinerea, it oscillates between the high and very high classes.
The number of sprays used in the calendar system was continuously greater than the necessary for the control of mildew and B. Cinerea.