{"id":282,"date":"2026-06-19T22:18:52","date_gmt":"2026-06-19T21:18:52","guid":{"rendered":"https:\/\/www.coltivobio.com\/en\/?p=282"},"modified":"2026-06-21T12:31:58","modified_gmt":"2026-06-21T11:31:58","slug":"grapevine-gray-mold","status":"publish","type":"post","link":"https:\/\/www.coltivobio.com\/en\/grapevine-gray-mold\/","title":{"rendered":"Grapevine gray mold: the best strategies for control and prevention"},"content":{"rendered":"

Botrytis, or gray mold, is one of the most common diseases affecting grapevines near harvest. In this technical guide, we will examine how to identify the disease and the correct management strategies in organic viticulture.<\/strong><\/p>\n

This article contains affiliate links. We may earn a commission from qualifying purchases<\/p>\n

Description and symptoms of botrytis<\/strong><\/h2>\n

Along with powdery mildew and downy mildew, botrytis is one of the most dangerous fungal diseases of grapevine. In addition to causing quantitative yield losses, it can significantly alter wine quality. The scientific name of this fungus is Botrytis cinerea<\/em>, while its sexual stage is known as Botryotinia fuckeliana<\/em>. The pathogen can also survive as a saprophyte on decomposing organic matter. Besides grapevine, many fruit and vegetable crops can be affected, including strawberry, apple, pear, peach, cherry, bean, and broad bean.<\/p>\n

\"
Figure 1 – Severe attack of Botrytis cinerea on grape clusters at harvest.<\/figcaption><\/figure>\n

How botrytis manifests on grapevine<\/strong><\/h2>\n

Also known as gray mold, botrytis appears on infected grape clusters as a characteristic gray fungal growth (see Figure 1). Affected tissues lose their firmness, and infected berries are irreversibly damaged.<\/p>\n

Table grapes affected by botrytis become unmarketable, while wine grapes undergo biochemical changes that negatively affect wine flavor and quality.<\/p>\n

Although clusters are the primary target, leaves and shoots may also be infected, although such infections are much less common. On leaves, symptoms appear as chlorotic areas that later become necrotic and, under favorable environmental conditions, develop a gray moldy growth. On shoots, infection is generally limited to green tissues and results in mild dieback with little tendency to spread. Likewise, infections of tendrils and petioles are rare and usually cause minimal damage.<\/p>\n

The fungus can penetrate the plant through two distinct pathways. The first occurs when tissues are still green and actively photosynthesizing, such as leaves, shoots, and immature berries. These tissues possess numerous stomata through which the pathogen can easily enter and colonize the host. Botrytis may also penetrate through the floral stigma, attracted by the secretions produced during flowering. When infection occurs through flowers or young clusters, it generally remains latent due to the low pH of immature berries.<\/p>\n

The second pathway is the most dangerous and economically important. It occurs during veraison, when berries no longer possess functional stomata. At this stage, the fungus can invade the host only through wounds caused by biotic factors (such as grape berry moths, thrips, or powdery mildew) or abiotic factors (such as hail or wind damage). During veraison, the decrease in organic acids and the increase in sugar content make the berries highly susceptible to destructive infections.<\/p>\n

Biological cycle of botrytis<\/strong><\/h2>\n

Botrytis cinerea<\/em> survives in the environment in several forms, including conidia, sclerotia, and overwintering mycelium beneath the bark. It can also survive as a saprophyte on plant debris.<\/p>\n

In early autumn, sclerotia begin forming on infected tissues. These appear as small black structures, only a few millimeters long, oblong in shape and hard to the touch, usually produced on canes.<\/p>\n

In spring, under suitable temperature and humidity conditions, the sclerotia, overwintering mycelium, and infected crop residues produce gray fungal growth consisting of conidiophores and conidia. The conidia are dispersed primarily by wind and are favored by rain splashes.<\/p>\n

Once deposited on plant tissues, infection can occur through stomata or wounds. The optimal conditions for conidial germination are approximately 15\u00b0C and 15 hours of leaf wetness. These conditions are commonly referred to as the “Rule of Two Fifteens.”<\/strong><\/p>\n

If berries at veraison have been damaged by biotic factors (powdery mildew, grape berry moths) or abiotic factors (hail, etc.), fewer hours of wetness are required for infection to occur.<\/p>\n

This climatic scenario also favors the development of overwintering mycelium present on bark and plant debris.<\/p>\n

Throughout the growing season, conidia are continuously produced, with production strongly correlated with rainfall. Generally, two peaks occur:<\/p>\n