Integrated Management of Black Rot (*Guignardia bidwellii*) in Vineyards: Diagnosis, Cycle, and Control Strategies

Symptomatic Identification and Life Cycle of Guignardia bidwellii

The black rot, caused by the fungus Guignardia bidwellii, represents one of the most destructive diseases in viticulture globally, significantly impacting grape production in regions such as Argentina and other parts of Latin America. This fungal pathology, which affects leaves, shoots, and crucially, the grape clusters, can lead to substantial economic losses if not managed properly. Implementing integrated control strategies is fundamental to safeguarding vineyard health and ensuring harvest quality, especially in a context of increasing climatic variability that can favor its development.

Early identification of black rot is essential for effective management. Initial symptoms manifest on leaves as small, circular, tan spots with a dark reddish halo, which over time develop small black dots, the pycnidia, in their center. On shoots, lesions are elongated and sunken. However, the most severe damage occurs on the fruit. Infected berries turn brown, then purple, and finally mummify, shriveling and becoming covered in pycnidia, transforming into hard, black structures that remain attached to the cluster or fall to the ground.

The life cycle of Guignardia bidwellii begins with the release of ascospores from the mummified fruits of the previous year, which are dispersed by wind and rain. These primary spores infect the young tissues of the vine. Subsequently, conidia (asexual spores) form in the pycnidia, which are dispersed by water splash and are responsible for secondary infections throughout the season. The disease is favored by temperatures between 20-27 °C and prolonged periods of leaf wetness, conditions that are increasingly frequent in some wine-growing regions due to climate change, demanding constant adaptation of management protocols.

Cultural Practices for Fungal Inoculum Mitigation

Cultural practices constitute the first line of defense against black rot, focusing on reducing inoculum and creating an environment less conducive to the fungus. The removal of pruning debris and, crucially, the collection and destruction of mummified clusters from the previous season are vital steps to reduce the source of primary spores. Light soil tillage in spring can help bury infected debris, decreasing ascospore release.

Canopy management is another fundamental pillar. Proper pruning that ensures good aeration and sunlight penetration into the cluster zone accelerates the drying of foliage and berries after rain or dew, hindering disease development. Techniques such as strategic leaf removal in the cluster zone improve these conditions. Likewise, selecting grape varieties with greater genetic resistance to black rot represents a long-term preventive strategy. Recent research is developing and evaluating new, more resilient varieties and clones, a key trend in sustainable viticulture. For more details on resistant varieties, one can consult the work of institutions like INTA: [https://inta.gob.ar/documentos/podredumbre-negra-black-rot-de-la-vid]

When environmental conditions are favorable for the disease or the inoculum pressure is high, chemical control becomes necessary, always within an integrated management program. The choice and timing of fungicide applications are critical. Protective treatments (e.g., based on mancozeb or folpet) should be applied before infection periods, forming a barrier on plant tissues. Systemic or translaminar fungicides (e.g., triazoles, strobilurins) can offer early curative control. It is crucial to rotate the chemical groups of fungicides to prevent the development of resistance in the fungal population.

Fungicide Applications and Biological Alternatives in Viticulture

Concurrently, biological alternatives are being explored and adopted as part of a more sustainable approach. Products based on antagonistic microorganisms, such as Bacillus subtilis or plant extracts, show potential for reducing disease severity. These biopesticides are especially valuable in organic production programs or for reducing chemical load in the environment. Integrating technologies like weather stations with humidity and temperature sensors, along with predictive infection risk models, allows for optimizing application timing, reducing the total number of treatments and improving their efficacy. This precision agriculture is a growing trend that maximizes resources and minimizes impacts. More information on the disease is available at: [https://www.infoagro.com/viticultura/enfermedades/podredumbre_negra.htm]

A successful black rot management program relies on constant monitoring and informed decision-making. Regular vineyard scouting to detect the first symptoms on leaves and shoots is fundamental. Using digital tools and mobile applications to record the presence and severity of the disease, as well as climatic conditions, allows for generating risk maps and making strategic decisions.

Implementing forecasting models based on degree-days and leaf wetness periods helps predict the moments of highest risk for primary and secondary infection. These systems alert growers to the imminent need for control measures, whether cultural or chemical. Combining this data with field observations and information on vine phenology (plant developmental stage) forms a robust and adaptive Integrated Pest Management (IPM) strategy, essential for resilient and productive long-term viticulture.

Monitoring Systems and Decision-Making for Black Rot Management

Controlling black rot in grapevines demands a holistic and adaptive approach that combines cultural practices, selective use of plant protection products, and the constant incorporation of technological innovations. From canopy management and inoculum elimination to the application of biopesticides and the use of predictive models, each component plays a critical role. Modern viticulture, facing climatic challenges and the demand for sustainability, benefits greatly from continuous research and the adoption of these integrated strategies. Investment in knowledge and technology not only protects the current harvest but also ensures the long-term viability and health of vineyards.