Defoliation of Grapes – But Beware of Sunburn

Not only humans need protection from UV rays – our grapes in the vineyards can also get sunburn. Once the berries start to soften, there's a risk that too much sunlight will cause their skin to crack, dry out, and turn blue or brown. Since grapes can’t use sunscreen, winegrowers must take viticultural precautions. As strange as it may sound, early defoliation of the grapes right after flowering is the best way to harden the berry skins. However, on hot summer days, defoliating or thinning out the canopy should be avoided to prevent overexposure to the sun.

When used purposefully and knowledgeably, defoliation offers many proven benefits for a wide range of grape varieties. After rainfall, grapes dry much faster due to better ventilation. Plant protection products are more effectively applied. The grapes also develop more intense aromas of yellow fruits (which may not always be desirable, for example in green-styled Sauvignon Blanc). Red grapes produce deeper color. Moreover, the dreaded pest, the spotted wing drosophila, prefers shady, humid conditions and tends to avoid defoliated vineyards.

In Rheinhessen, defoliation is rarely done by hand nowadays. We're currently witnessing tremendous technical advances. What started with mechanically plucking leaves is now done using impulsive air pressure – the leaves are literally "blown off." This minimizes mechanical stress on the grapes and even removes dried flower caps or damaged berry parts, helping prevent grape rot. Often, removing the leaves only on the shady side is enough to avoid sunburn.

Thus, defoliation remains one of the most important tools in shaping wine quality.