Last updated on October 23rd, 2023 at 11:04 pm
When the leaves on roses have holes and are partially pitted, most often, leaf damage of this type occurs from May.
The larvae of very different genera of leaf wasps are responsible. The newly hatched larvae cause this typical damage with their feeding activity.
Normally, the occurring damage is small, so you can limit yourself with the control of the larvae to a collection by hand (if you can overcome yourself). Or you can leave this work to the hungry birds; they are grateful for the protein-rich food and feed their brood with it.
In case of very heavy infestation, i.e. when almost all leaves are gnawed and perforated (and really only then), we recommend Neudorff. The agent is harmless for other animals.
I also have leaf wasp larvae on my roses every year. They look like butterfly caterpillars. The young larvae first scrape the leaves, later they also eat holes in them. When the infestation gets too bad I spray the leaves with a soft soap solution. I would not use Spruzid, because it harms some beneficial insects. Besides leaf wasps, butterfly species are also leaf feeders, e.g. moths.
If the leaves on your roses are perforated and pitted, it is likely that your roses are dealing with a common fungal disease known as “Rose Black Spot” (Diplocarpon rosae). This disease is a frequent problem for rose growers and can lead to a decline in the health and appearance of the plants if not properly managed.
Here’s what you can do to fix the problem:
1. Prune Affected Leaves:
- Begin by pruning and removing the affected leaves. This helps reduce the spread of the disease and allows for better air circulation within the plant.
2. Proper Watering:
- Water your roses at the base rather than from overhead. This helps keep the foliage dry, making it less conducive for the fungal spores to thrive. Avoid wetting the leaves if possible.
3. Mulch and Soil Management:
- Apply mulch around the base of your roses to prevent soil splash, which can carry fungal spores to the leaves. Ensure good drainage and avoid overwatering, as overly wet conditions can promote fungal growth.
4. Fungicide Treatment:
- Consider using a fungicide specifically designed for controlling Rose Black Spot. Follow the manufacturer’s instructions for application, and start treatment early in the growing season to prevent the disease from spreading.
5. Resistant Rose Varieties:
- When selecting new rose varieties for your garden, consider choosing those known for their resistance to Rose Black Spot. These varieties are less likely to be affected by the disease.
6. Proper Pruning and Thinning:
- Prune your roses to encourage good air circulation, which can help prevent fungal diseases. Thinning the interior of the plant allows air and sunlight to reach the center.
7. Remove Fallen Leaves:
- Remove and dispose of fallen leaves promptly, as they can carry fungal spores. Do not compost infected plant material.
8. Organic Remedies:
- Some organic treatments, like neem oil or a baking soda solution, can help control Rose Black Spot. These remedies are less harmful to the environment and can be used as preventive measures.
9. Regular Inspection:
- Keep a close eye on your rose bushes throughout the growing season. Early detection and intervention can help prevent the disease from becoming severe.
Rose Black Spot can be challenging to control, and it may require a combination of these strategies to effectively manage it. It’s important to be persistent in your efforts to keep your roses healthy and looking their best. If the problem persists or worsens despite your best efforts, you may want to consult with a local nursery or extension service for further guidance and possible treatment options.