If you’ve noticed small, raised spots on your grapevines, you’re likely dealing with bumps on grape leaves. These tiny raised leaf spots can be alarming, but understanding their cause is the first step to managing them.
This guide will help you identify what’s causing those bumps, figure out if it’s a serious problem, and show you exactly what to do about it. We’ll cover everything from common pests to fungal issues so you can get your vines back to full health.
Bumps On Grape Leaves – Tiny Raised Leaf Spots
Those little bumps aren’t random. They are a specific symptom with a few likely culprits. The most common causes are insects, mites, or diseases. The appearance of the bump—its color, shape, and location—holds the key to proper identification.
Let’s break down the possibilites so you can become a detective in your own vineyard or garden.
Common Causes of Bumps and Raised Spots
Here are the primary offenders that create bumps on grape foliage.
1. Grape Phylloxera (Leaf Form)
This is a major suspect. Phylloxera are tiny, aphid-like insects that feed on roots and leaves. The leaf form causes distinctive galls.
- Appearance: Small, green or reddish, wart-like bumps on the upper leaf surface. The underside will have a corresponding concave spot, often with a tiny insect inside.
- Impact: Leaf galls are mostly a cosmetic issue and rarely harm vine health significantly. The root form of phylloxera is far more devastating.
2. Grape Erineum Mite (Blister Mites)
These microscopic mites are a frequent cause of leaf bumps, creating a symptom called erineum.
- Appearance: Felt-like, fuzzy patches on the leaf underside, which correspond to raised, blister-like bumps on the top surface. The fuzz can be white, pinkish, or yellow.
- Impact: Usually minor, but severe infestations can reduce photosynthesis and weaken the vine over time.
3. Grapevine Leafroll Disease
This is a serious viral disease, and leaf symptoms can sometimes include puckering.
- Appearance: Leaves roll downward and develop a thick, leathery texture. In red varieties, leaves turn deep red between the veins while veins stay green. The “bumps” are more of a general puckering rather than distinct spots.
- Impact: Severe. It reduces fruit quality, delays ripening, and lowers yields. There is no cure.
4. Fungal Diseases (Like Anthracnose)
Some fungal issues can cause raised lesions.
- Appearance: Anthracnose causes small, sunken spots with dark edges and raised centers, which can make the leaf feel bumpy. The centers may fall out, creating a “shot-hole” effect.
- Impact: Can defoliate vines and affect fruit, especially in wet, warm climates.
Step-by-Step: How to Diagnose Your Grape Leaves
Follow these steps to pinpoint the problem.
- Examine the Bump Closely: Use a magnifying glass. Look at both the top and bottom of the leaf. Is the bump smooth or fuzzy? Is there an insect visible inside?
- Check the Pattern: Are the bumps isolated or covering the whole leaf? Are they only on new growth or also on older leaves?
- Look for Other Symptoms: Check for leaf discoloration, rolling, or fruit issues. Also inspect the canes and trunk for any abnormalities.
- Consider the Time of Year: Phylloxera galls often appear in late spring. Erineum mite damage is most visible in early to mid-summer.
Treatment and Management Strategies
Your action plan depends entirely on the diagnosis. Here’s what to do for each cause.
Managing Grape Phylloxera (Leaf Galls)
Since leaf galls are not very harmful, treatment is often unnecessary. Focus on overall vine health.
- You can simply pinch off heavily infested leaves and dispose of them in the trash.
- Avoid over-fertilizing with nitrogen, as succulent new growth attracts pests.
- For severe cases, horticultural oil applied at the dormant season or delayed-dormant stage can help smother overwintering eggs.
Controlling Grape Erineum Mites
These mites live inside the leaf, making them hard to reach with sprays.
- Prune and destroy affected leaves as soon as you see them in early summer to reduce mite populations.
- Dormant season applications of horticultural oil or lime-sulfur are the most effective controls, as they target the overwintering mites before they enter the leaf.
- Miticide sprays during the growing season are rarely effective because the leaf fuzz protects the mites.
Dealing with Grapevine Leafroll Disease
There is no treatment for this virus. Management focuses on prevention and containment.
- Purchase certified virus-free plants from reputable nurseries. This is the most critical step.
- Remove and destroy infected vines to prevent spread to healthy ones, as the virus is transmitted by mealybugs and scale insects.
- Control those insect vectors with appropriate insecticides or biological controls.
Fighting Fungal Diseases
Good sanitation and fungicide timing are key.
- Prune vines to improve air circulation and reduce leaf wetness.
- Clean up and destroy all fallen leaves and debris in autumn.
- Apply fungicides like copper-based sprays or sulfur early in the season, starting when new shoots are a few inches long, especially if you’ve had problems before.
Prevention is the Best Medicine
Keeping your vines healthy from the start is easier than fixing a problem. Here’s your prevention checklist.
- Choose Resistant Varieties: Some grape rootstocks are resistant to the root form of phylloxera. Research varieties suited to your area’s common problems.
- Plant Properly: Ensure good spacing and site vines in full sun with excellent air flow.
- Prune Correctly: Annual pruning maintains structure, improves air circulation, and reduces pest hiding spots.
- Water Wisely: Use drip irrigation instead of overhead watering to keep leaves dry and prevent fungal spores from spreading.
- Monitor Regularly: Walk your vineyard or garden weekly during the growing season. Catching issues early makes all the difference.
- Maintain Soil Health: Balanced nutrition and proper pH helps vines resist pests and diseases more effectively.
When to Call a Professional
Most leaf bump issues can be managed at home. However, seek expert help if:
- You suspect Leafroll virus, as it requires confirmatory testing and has major implications for your whole vineyard.
- The problem is widespread and rapidly defoliating your vines despite your efforts.
- You are unsure of the diagnosis and want to avoid applying the wrong treatment, which can waste time and money.
Your local county extension office is a fantastic, often free, resource for plant disease diagnosis and advice tailored to your region.
FAQ: Quick Answers About Grape Leaf Bumps
Q: Are the bumps on my grape leaves harmful?
A: It depends. Phylloxera leaf galls and erineum mite damage are usually cosmetic. Fungal spots or viral symptoms like leafroll are more serious and can affect fruit and vine longevity.
Q: Can I still eat grapes from a vine with bumpy leaves?
A: Yes, in most cases. The fruit is not affected by pests like phylloxera or erineum mites. However, if the issue is a severe fungal disease that has spread to the fruit clusters, those grapes should not be consumed.
Q: What do mite bumps on grape leaves look like?
A: Erineum mite damage creates a distinct fuzzy, matted patch (like felt) on the leaf underside, with a corresponding raised blister on the top. This is different from a smooth, insect-filled gall.
Q: How do you treat blisters on grape leaves?
A: First, identify the cause. For mite blisters, remove affected leaves and use a dormant oil spray in late winter. For fungal issues, improve air flow and use preventative fungicides. There is no cure for viral blisters or puckering.
Q: Should I remove leaves with bumps?
A: For light infestations of pests like phylloxera or erineum mite, removing a few affected leaves can help reduce populations. For widespread issues, leaf removal isn’t practical and may stress the vine; broader management is needed.
Finding bumps on your grape leaves can be a worry, but now you have the knowledge to identify and adress the issue. Start with a close inspection, match the symptoms, and choose your response based on the cause. Remember, healthy vines are resilient vines. With good care and vigilant monitoring, you can keep those tiny raised leaf spots from becoming a big problem and enjoy a healthy harvest for seasons to come.