Brown spots on grapes are common, whether in a home garden or at the grocery store. These discolorations often raise questions about the fruit’s health and edibility. Understanding their appearance and causes helps identify issues and determine next steps.
Understanding Different Brown Spot Appearances
Brown spots on grapes vary in appearance, offering visual cues about their origin. They can be small, circular lesions, sometimes sunken with a darker border or lighter center, creating a “bird’s-eye” look. Other spots might be irregular blotches spreading across the berry.
Their texture also varies, from firm to soft or shriveled, feeling dry and hard or mushy. Spots can appear on individual berries, entire clusters, or even on leaves and stems.
Primary Causes of Brown Spots on Grapes
Brown spots on grapes stem from several factors, including fungal diseases, environmental stressors, and physical damage. Each cause leaves distinct marks, allowing for identification.
Fungal diseases are frequent culprits. Black Rot, caused by the fungus Guignardia bidwellii, initially appears as small, circular, tan spots with a red margin on leaves. On berries, these spots start as light or purple-brown, expanding to cover the entire fruit before it shrivels into a hard, black “mummy.” Anthracnose, also known as bird’s-eye rot, caused by Elsinoe ampelina, creates circular, chocolate brown spots on leaves, which may later become bleached in the center. On grapes, anthracnose presents as sunken, purplish-brown spots with a lighter center, resembling a bird’s eye, and can lead to cracking. Downy mildew, caused by Plasmopara viticola, manifests on leaves as yellow “oil spots” that turn reddish-brown along veins. Infected young berries may turn light brown, become soft, and shrivel.
Environmental factors also contribute to brown spots. Sunburn occurs when grapes are exposed to excessive sunlight, high temperatures, and UV radiation, particularly after véraison (the onset of ripening). Symptoms range from yellow, brown, or bronze spots on the sun-exposed side of the fruit to complete desiccation. Sunburned grapes may appear as white, brown, or yellow blotches that can initially be soft but later dry up, making the berry hard on one side.
Physical damage can also lead to brown spots. Bruising, which often results from mishandling during growth, harvest, or transportation, causes brown discolorations on the grape skin. Bird pecks are another form of physical damage, leaving small puncture marks on the fruit. These open wounds can then become entry points for secondary infections by fungi or bacteria, leading to further browning and decay.
Safety Concerns for Grapes with Brown Spots
When encountering grapes with brown spots, a common concern is whether they remain safe to eat. Grapes with minor brown spots are edible if they remain firm and juicy. Thoroughly washing grapes before eating, regardless of spots, is always a good practice.
However, certain conditions indicate that grapes should be avoided. Grapes that are mushy, extensively brown, or wet to the touch should be discarded, as these signs often suggest significant decay or mold growth. If an unpleasant odor, such as vinegar, acidity, or mustiness, is present, or if there is visible mold, particularly around the stem or where the skin is broken, the grapes should not be consumed. While black rot can cause grapes to shrivel into hard mummies, and anthracnose can lead to cracking, consuming fruit with extensive fungal development is not advisable.
Strategies for Prevention and Management
Preventing brown spots on grapes involves cultural practices that promote vine health and reduce disease pressure. Implementing good sanitation is a foundational step. This includes removing and destroying infected plant material, such as mummified berries and diseased canes, especially during the dormant season, to reduce overwintering fungal spores. Cultivating the soil under vines before bud break can also help bury spores.
Proper pruning and canopy management are also important. Pruning grapevines during late winter or early spring, before bud break, helps improve air circulation within the canopy and allows for better sunlight penetration to the fruit. This increased airflow helps dry moisture from leaves and berries, creating an environment less favorable for fungal diseases like black rot and downy mildew. Removing some leaves around grape clusters after fruit set can also enhance air movement and sun exposure, helping fruit ripen and reduce disease risk.
Selecting disease-resistant grape varieties can significantly reduce brown spots caused by common fungal pathogens. Some cultivars exhibit greater resistance to specific issues like black rot or downy mildew. Regular monitoring of vines allows for early detection of problems, enabling timely intervention before issues become widespread.