Hot and dry weather anticipates part of the 2013 grape harvest and the total produced could exceed 2012

For the third consecutive harvest we are going through a relatively dry period, with rainfall occurring in amounts below the Climatological Normal (average that considers the period 1961 to 1990).

In the 2010/11 harvest, the months of October, November and December had lower rainfall totals than normal, which mitigated the occurrence of diseases and made it easier for farmers to carry out phytosanitary management practices. The situation changed at the end of January, when it rained regularly and in greater quantities again. With a mild drought and environmental conditions unfavorable to the occurrence of diseases, the 2011 harvest was a record, reaching 709 thousand tons of grapes in the State of Rio Grande do Sul.

In the 2011/12 harvest, a similar situation was repeated, only this time with greater intensity. From October to March, all months, except February, had less rainfall than the climatological normal. In November, the driest month, the rainfall recorded at the EMBRAPA Grape and Wine station was 23 mm, while the normal average for the month is 140 mm. In early December there were reports of death of vines in areas with shallow soils. The estimated losses in this harvest, due to drought and hail, were around 20% in relation to the 2010/11 harvest.

In the current 2012/13 harvest, a similar situation occurs again, with little rain at the beginning of the cycle. November had a cumulative total of 24 mm, concentrated in the last days of the month (Figure 1). The occurrence of few clouds and absence of rain favored the predominance of sunny days. This situation led, throughout Nov. and early December, conditions for the occurrence of progressively hotter and drier days. However, the dry period ended with the rains that began to occur from mid-December and intensified at the end of the month.

Average temperatures in October, November and December remained above the normal average (Figure 2). This condition determined that some early varieties (such as Vênus and Niágara), normally harvested in December, were harvested earlier, as reported by producers in Serra Gaúcha. This occurs because, the higher the temperature, the higher the metabolic rate and rate of development of the vines, and of plants in general. In other words, the entire plant cycle is anticipated, favoring early budding, flowering, fruiting and maturation.

The predominance of sunny and dry days also contributed to reducing the occurrence of diseases and reducing the need for fungicide applications against diseases. Until the first ten days of December, the incidence of downy mildew in vineyards in Bento Gonçalves has remained below average. On the other hand, there was a higher incidence of powdery mildew, a disease typical of regions with a dry and hot climate (e.g., the northeast of the country). As powdery mildew control requires different treatment compared to downy mildew, early identification of the disease is a crucial step for greater control effectiveness.

Despite the water deficiency observed in the State of Rio Grande do Sul in November, there is still no threat to the productivity of Rio Grande do Sul's vineyards. In October, the soils had high levels of water storage. Rainfall that month totaled 151 mm – close to the normal value of 156 mm. Thus, although the rain in November was approximately the same as that in November 2011, the water deficiency in the grape crop was not as intense. In addition to this fact, the rains that occurred in the second and third ten days of December 2012 interrupted the sequence of days in which the crop was experiencing water deficiency, and partially recovered water storage levels in the soil.

In the current scenario, analyzed until the end of December, it is not possible to accurately estimate the outlook for the 2013 harvest for all grape cultivars, but it can already be estimated for a good part of them. The period between November and the beginning of January is the most important for defining the productive potential, as it corresponds to the fruit filling phase. In this way, the productive potential is already practically guaranteed, because even if a dry period occurs again from January onwards, at this moment the soils in the producing regions are at their maximum storage capacity.

According to the consensus climate forecast, prepared jointly by the Center for Forecasting and Climate Studies (CPTEC) and the National Institute of Meteorology (INMET), the quarters of January, February and March should present a total rainfall above the normal range in Rio Grande do Sul and Santa Catarina. In this case, the probability of seeing a dry period again is very small.

In this context, the environmental conditions observed to date place the productive potential of the current harvest in an intermediate position between the 2011 and 2012 harvests. Neither as favorable to productivity as that of 2011, nor as unfavorable as that of 2012. Therefore, unless Unforeseen events with adverse meteorological phenomena such as hail in 2012, or excessive rainfall during ripening which would lead to losses due to disease, it is very likely that the 2013 harvest will surpass the 2012 harvest in quantity (Figure 3).

Finally, it is always interesting to remember that the total amount of grapes produced each year does not only depend on environmental conditions, but also largely depends on the decisions made by each producer, always greatly influenced by market perspectives and grape prices. Various management actions carried out throughout the crop cycle affect grape productivity and quality, such as: fertilization, pruning, pest and disease control. The environment defines the production potential, while crop management, that is, the agronomic techniques used, defines how much of this potential will be used.