Brown Spots On Grapes

You’ve brought home a beautiful bunch of grapes, only to notice unsightly and concerning blemishes. Those brown spots on grapes can be a real letdown, making you wonder if they’re safe to eat or a sign of a bigger problem in your own vineyard. As a gardener, I see this question all the time. Let’s look at what causes these marks and what you can do about them, whether you’re a home grower or just a careful shopper.

First, don’t panic. Not all brown spots mean the fruit is ruined. Some are purely cosmetic, while others indicate disease. The key is learning to tell the difference. This knowledge helps you save your harvest, make better choices at the store, and enjoy your grapes with confidence.

This heading covers the main reasons you’ll see those marks. Think of it as a diagnosis guide. We’ll break down each cause, from harmless to serious, so you can identify what you’re dealing with.

Common Causes of Brown Spots

Grapes are susceptible to several issues that manifest as brown spots. The environment, fungi, bacteria, and even the plant’s own biology can be the culprit. Here’s a rundown of the usual suspects.

Sunburn (Sunscald): Just like our skin, grape berries can get sunburned. This happens during hot, dry periods, especially if leaf cover is thin. The spots are typically hard, dry, and sunken, appearing on the side of the berry facing the sun.
Phomopsis Cane and Leaf Spot: This fungal disease causes small, dark spots with a yellowish ring on young leaves and shoots. On berries, it creates dark, irregular spots that can make the fruit crack.
Anthracnose (Bird’s Eye Rot): This fungus gives a very distintive look. It starts as small, circular, reddish-brown spots that later develop grayish-white centers with dark borders, resembling a bird’s eye.
Black Rot: A devastating fungal disease. It begins as small, whitish dots on young berries that expand into large, sunken brown rot covering half the berry. The berries eventually shrivel into hard, black “mummies.”
Powdery Mildew: While often seen as a white powder on leaves, it can affect berries too. Infected young berries may have rusty brown net-like patterns or split open. Older berries show discolored, dull patches.
Downy Mildew: This causes reddish-brown spots on the top of leaves and a fuzzy white growth underneath. On berries, it leads to a leathery, brown discoloration, and they often shrivel and drop.
Insect Damage: Pests like grape berry moth larvae feed inside berries, creating holes and causing secondary rot that appears as a brown spot. Stink bug feeding can also cause small, hard, brown spots where they pierced the skin.

Are Grapes with Brown Spots Safe to Eat?

This is the most common question. The answer depends entirely on the cause.

Grapes with spots from sunburn or light insect damage are generally safe to eat. Simply cut away the affected area, much like you would with a bruise on an apple. The rest of the fruit is perfectly fine.

However, you should avoid eating grapes that show signs of fungal diseases like black rot or powdery mildew, especially if the berries are mushy, leaking, or smell off. While most plant fungi aren’t toxic to humans, they can cause stomach upset for some people, and the flavor will be poor. When in doubt, throw it out.

Prevention and Control in Your Garden

An ounce of prevention is worth a pound of cure, especially in gardening. Managing brown spots starts long before you see them. A proactive approach is your best defense.

Cultural Practices for Healthy Vines

Good garden hygiene and vine management create an environment where diseases struggle to take hold.

Prune for Airflow: Prune your vines diligently to create an open canopy. Good air circulation dries leaves and fruit quickly after rain or dew, making it harder for fungi to germinate.
Clean Up Debris: In fall and early spring, remove and destroy all fallen leaves, pruned canes, and any “mummified” fruit left on the vine or ground. This debris harbors overwintering spores.
Water at the Roots: Use drip irrigation or soaker hoses instead of overhead watering. Wet foliage is a breeding ground for disease.
Site Selection: Plant grapes in full sun with excellent air drainage. Avoid low, damp spots where cold air and moisture settle.
Balanced Nutrition: Avoid excessive nitrogen fertilizer. It promotes lush, soft leaf growth that is more susceptible to diseases. A soil test can guide your fertilizing plan.

Organic and Chemical Treatment Options

When cultural practices aren’t enough, targeted treatments can help. Always choose the right product for the specific problem.

Identify the Problem Correctly: Misdiagnosis leads to wasted effort. Use this guide or consult your local extension service to be sure.
Start Early: Fungicide sprays are primarily protective, not curative. Begin applications before symptoms appear, often at bud break and continuing on a schedule through the growing season.
Organic Choices: Sulfur and copper-based fungicides (like Bordeaux mixture) are classic organic options for many fungal diseases. Neem oil can help with powdery mildew and some insects. Always follow label directions, as even organic products can harm plants if misused.
Synthetic Fungicides: For severe, recurring problems, products containing myclobutanil or captan may be necessary. Rotate different chemical classes to prevent pathogen resistance.
Apply Thoroughly: Cover all surfaces of the vines, especially the new growth and developing fruit clusters. Reapply after heavy rain.

Step-by-Step: Managing an Outbreak

If you already have brown spots, here’s your action plan to salvage the situation.

Assess the Damage: Walk through your vineyard and determine how widespread the issue is. Is it on one cluster or many? One vine or the whole row?
Remove Infected Material: Immediately prune off and destroy badly infected fruit clusters, leaves, or canes. Do not compost them; bag and trash them to remove the spore source.
Apply Treatment: Based on your diagnosis, apply the appropriate fungicide or treatment. Be sure to cover the undersides of leaves.
Adjust Watering: Ensure you are not contributing to the problem. Check that your irrigation isn’t wetting the foliage.
Monitor Closely: Keep a close eye on the vines over the next two weeks. Look for any new spots appearing on previously healthy growth.
Plan for Next Year: Note the problem and start your preventative spray schedule earlier next spring. Consider if you need to improve pruning for better airflow.

Selecting the Best Grapes at the Store

You can use this knowledge to pick better fruit at the market. A little scrutiny goes a long way.

Look for Uniform Color: Choose bunches where the grapes are a consistent color, whether green, red, or purple. Avoid bunches with many dull or brownish berries.
Check the Stem: The stem should be green and flexible, not dry and brittle. A healthy stem often indicates fresher fruit.
Inspect for Firmness: Gently shake the bunch. Grapes should be plump and firmly attached. Be wary of any that are shriveled or have leaking spots.
Give it a Sniff: A sour or off smell is a clear sign of decay, even if you can’t see it yet.

FAQ: Your Questions Answered

Can I just wash off the brown spots?

No, washing will not remove fungal spots or sunburn. These blemishes are damage to the skin and flesh of the grape. You can wash away surface dirt, but the spot itself is permanent.

What causes brown spots on grape leaves?

Many of the same diseases that affect fruit also cause spots on leaves, like Phomopsis, Black Rot, and Downy Mildew. Nutrient deficiencies or herbicide drift can sometimes cause brown leaf spots too.

Are brown spots on grapes mold?

They can be. Fungal diseases like black rot or powdery mildew are essentially types of mold. Other causes, like sunburn or insect damage, are not mold-related.

How do you treat black rot on grapes?

Black rot requires a aggressive strategy. Remove and destroy all infected material immediately. Apply a fungicide labeled for black rot (like mancozeb or myclobutanil) on a 7-14 day schedule from bud break through fruit set. Prevention is critical, as it’s very hard to control once it’s established in the berries.

Can I use vinegar to treat grape diseases?

While vinegar has antifungal properties, it is not a reliable or recommended treatment for grape diseases. It can easily damage the delicate vine tissues and fruit. It’s better to use approved horticultural products designed for this purpose.

Why do my grapes have brown spots after picking?

Spots that appear after harvest are often due to handling damage that leads to bruising and decay, or they could be the continuation of a disease that was already present but not yet visible at picking time. Always handle clusters gently and store them in a cool, dry place.

Long-Term Vine Health

Building resilience in your grapevines is a multi-year effort. Healthy vines resist problems better and recover quicker when stressed.

Start with disease-resistant varieties if you live in a humid area prone to fungal issues. Research which cultivars do well in your local climate. Ensure your vines are properly trained on a sturdy trellis system to keep fruit and leaves off the ground and allow for good air movement. Conduct regular soil tests to maintain proper pH and nutrient levels, because a well-fed plant is a strong plant. Finally, be observant. Walk your vineyard weekly during the growing season. Catching a problem when just a few leaves are affected makes all the difference. Early intervention is always more successful than a last-minute rescue attempt.

Remember, seeing a few brown spots doesn’t mean you’ve failed. Gardening is a constant learning process with nature. Each season provides new clues and chances to improve. By understanding the reasons behind these blemishes, you take the first step toward a healthier, more productive vineyard or simply become a more informed consumer, able to choose the best fruit for your table.