Opportunities and challenges of mid- to late-season drought in vineyards
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EmailFacing mid- to late-season drought stress in Michigan vineyards? This article provides crucial strategies to manage this emerging issue and keep your vines healthy. Explore essential tips for handling drought and ensuring a successful harvest.
Mid- to late-season drought stress has become a new phenomenon in Michigan vineyards, affecting some years more severely than others, particularly in vineyards without irrigation systems. While dry, sunny weather during this period typically benefits grape quality by reducing fungal disease and bunch rot, the lack of sufficient water can cause significant stress to the vines. Factors such as rootstock, vine age and soil type play a crucial role in how well vineyards can cope with drought. Understanding these interactions is key for vineyard managers to effectively mitigate the impact of drought stress.
Recognizing early drought stress symptoms
The visual signs of drought stress in vineyards are not always immediately apparent. Leaves may still look healthy, but one key indicator is their temperature. If the leaves feel unusually warm to the touch, it suggests the vines have closed their stomata to conserve water. This closure halts gas exchange, stopping photosynthesis and potentially disrupting the ripening process.
Additionally, the tips of grapevine shoots under drought stress often straighten, losing their typical curved shape—a subtle but important early sign of stress.
Vulnerable rootstocks and soil types
Michigan vineyards often use the 101-14 rootstock, which is known for its shallow root system. This rootstock is particularly prone to drought stress as it cannot access deeper soil moisture. Furthermore, the sandy soils common in many Michigan vineyards have a low water-holding capacity, making vines on these soils more vulnerable to dehydration during dry periods.
Read more about grape rootstocks for Michigan from Michigan State University Extension.
Managing canopy for drought and heat stress
While fruit-zone leaf removal has many benefits, vineyards that undergo severe leaf removal, especially hand removal that takes entire leaves, are more vulnerable to drought and heat stress during a dry mid/late season. When grape clusters are exposed to direct sunlight, their temperature can exceed the ambient air temperature, increasing the risk of sunburn and heat damage. To mitigate this, it’s crucial to practice careful leaf removal early in the season, particularly from fruit set to bunch closure, and leave enough canopy to protect clusters during drought or heat spikes. Mechanical leaf removal is recommended, as it leaves partial canopy coverage to shield the fruit.
Tips to mitigate drought stress
Vineyard floor management
Vineyard floor management involves careful consideration of the vegetation between vine rows. Studies indicate that alleyway vegetation typically doesn't compete with vines for water. However, dense or tall cover crops can pose challenges during dry periods. During dry periods, it's advisable to mow these areas, but avoid cutting too short, as this can expose bare soil to dry air and worsen drought stress. Proper management of cover crops helps balance the benefits of cover crops with potential water competition, encourages natural mulch formation, and supports soil moisture retention and vine health.
Mulching
Applying organic mulch such as straw around the base of vines is an effective way to maintain soil moisture levels. Mulch reduces water evaporation and provides a cooler root environment, helping vines withstand periods of drought.
Reflective film coverage
Applying light-colored particle films, such as kaolin clay (marketed as Surround), can help reflect sunlight and reduce the temperature of the vine canopy and fruit. This can lower the risk of drought and heat stress and improve berry anthocyanin concentration, which is crucial for grape quality. However, these films may need to be washed off before harvest to prevent any unwanted effects on wine flavor.
Soil amendments
Incorporating organic matter into the soil can increase its water-holding capacity, making it more resilient during dry periods. This can be achieved by adding compost or other organic materials that improve soil structure and moisture retention.
Efficient irrigation
If irrigation is available, using a drip irrigation system ensures water is delivered directly to the root zone, minimizing waste and maximizing efficiency. Timing and precision in irrigation are key to supporting vines through mid and late-season drought stress.
Conclusion
Effectively managing mid- to late-season drought stress in Michigan vineyards involves a multifaceted approach. This includes understanding rootstock vulnerabilities, adjusting canopy management, and enhancing soil health. While dry weather can improve grape quality by reducing disease pressure, it is crucial to address drought stress to maintain a healthy vine canopy and ensure a successful harvest. Adopting practices such as vineyard floor management, mulching, using particle films, and implementing efficient irrigation can significantly help vines endure the challenges of late-season drought conditions.
