Rioja wrangles with mildew
Producers in the Spanish wine region of Rioja are tackling the challenges of a damp 2025 growing season, and preparing for the hazards that come with it.
By the end of the first week of June, Rioja had experienced a meteorological smorgasbord – heavy rainfall, humidity, strong winds and then warm temperatures – a couple of weeks prior there had even been a small amount hail. As a visitor to the region, this erratic weather is a minor inconvenience when it comes to knowing what to pack, but for grape growers, it’s a headache that could make or break that year’s crop.
The topic which is on the mind of every viticulturist in Rioja, and is cropping up time and time again in local news outlets such as La Rioja, is fungal disease infecting the vines.
David González, head winemaker of the Perelada-owned Viña Salceda, said: “We have had a lot of problems with mildew – there was a lot of rain.”
“2023 and 2024 were dry vintages, but this year is the opposite,” he explained.
The two types of mildew which give viticulturists such grief are downy and powdery.
Explaining the symptoms of downy mildew, Rosana Lisa, Ramón Bilbao’s director of wine innovation, shared: “You’ll see yellowish ‘oil spots’ on the leaves, which hinder the plant’s ability to photosynthesise. When the disease appears on shoots and canes, the impact on production is even greater. As for the grape clusters, downy mildew affects quality by preventing proper ripening and significantly reduces yield.”
As for powdery mildew, Lisa noted that it “spreads more easily than downy mildew, even in dry conditions, and can propagate in cloudy weather conditions”.
“On the leaves, white spots appear; these can expand and eventually cause the leaf to dry out completely, stopping photosynthesis,” she continued. “The flowering period is when powdery mildew has the greatest impact on production, as affected leaves are completely lost. Regarding the berries, they become covered in a white powder, which prevents their development and leads to cracking, making them vulnerable to other diseases.”
Fighting back
Mildew is not a novel threat – winegrowers have developed an arsenal of techniques to combat it over the centuries.
“We try to only use ecological products like copper sulphates, but this year in some places we need to use other products,” said González. “This is the first time since 2020 that we have had a big mildew problem, and the pandemic caused management problems there!”
At present, copper sulphate is being sprayed on the Viña Salceda vines every week, with Ramón Bilbao also deploying such treatments.
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“We prioritise proactive measures to tackle potential issues in our vineyards. With weather stations installed directly within our vineyards, we get detailed 48-hour climate forecasts. This crucial information helps us manage the vineyard to prevent fungal outbreaks,” said Lisa.
There is another weapon at the disposal of producers – ventilation.
“Leaf removal on the north side of the vines is a common practice in Rioja Alta vineyards,” Lisa revealed. “This technique promotes better air circulation around the grape clusters, reducing humidity and fungal risk.”
Another technique to achieve this is to reduce planting density – for DOCa Rioja, the minimum planting density permitted is 2,850 vines per hectare, whereas the maximum is 10,000.
Better air circulation is one asset of higher-altitude plantings, something which Viña Salceda is increasingly going for, with the more exposed vineyards generally having fewer problems with mildew.
“But for vineyards down by the Ebro river, it’s more dangerous,” warned González.
A complex picture
As mentioned, mildew in vineyards is nothing new, but it is becoming increasingly unpredictable, as Lisa explained: “The effects of climate change are evident in the varying impacts across different regions. Some cooler areas which are getting drier and warmer actually become healthier. Meanwhile, other regions shift from cold to moderately cold, which increases their susceptibility to fungal diseases.”
“On the other hand,” she continued, “climate change is also noticeable in the extreme impact of meteorological phenomena. Years with excessive rainfall, for instance, can lead to a surge in fungal incidence.”
It is still too early to tell what the conditions of the growing season so far will mean for the vintage. By the time of my visit at the beginning of the month, fruit set was underway and expectations were, as they often are, cautiously optimistic, but they will not be sitting back and relaxing this summer.
“At the moment, I visit the vineyards once a month, in July and August once a week, and after that every two days,” revealed González.
Asked when he finds time to take a holiday, he quipped in response: “Holiday? What’s that?”
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