Roses are most certainly among the most beautiful flower-bearing shrubs, but they are also among the most vulnerable to diseases.
Although they may be fragile, their diseases can be mastered!
Regular and often organic care helps eradicate or prevent many rose tree parasites and diseases.
Aphids on rose trees
Here a few solutions to get rid of aphids naturally on rose trees:
Fermented stinging nettle or fern tea
This is an excellent 100% organic way of fighting aphids.
Read here on how to make your own stinging nettle tea.
Made with Marseille soap or beldi soap dissolved in water and sprayed on the plant, this soap mix makes it hard for aphids to stick to leaves.
Grate 5 oz (150 grams) of soap and dissolve it in 1 quart (1 liter) water, add and mix in 1 tablespoon vegetable oil. Spray on plants.
- Here are all our tips to fight aphids.
Rose tree rust
This is the most common fungus to attack rose trees.
It creates orange-rust colored blisters on the underside of leaves that show on the top side with small yellow-red-brown halos.
Effective treatment products are often sold against rose tree diseases and can also be used on all other plants.
- They usually are fungicides that work both preventively and curatively.
- As soon as the first symptoms appear, you must quickly remove all infected leaves and burn them.
- Prune your rose trees well, and give them space to ensure air circulation among the leaves.
Here are all our tips on how to effectively fight rust.
Rose tree chlorosis
This is one of the major issues that rose trees face, which has distinctive symptoms: yellowing of leaves that follows leaf discoloration.
Rose tree chlorosis is connected to the soil, often too poor, heavy and chalky. This prohibits the shrub from extracting much-needed iron from the soil.
Symptoms are very clear, and treatment is quite easy to apply.
- Provide good compost upon planting
Every winter, mix horse manure into the soil. If the disease is already declared, there are anti-chlorosis treatments sold in garden stores that help the rose tree to harvest the iron it needs.
Powdery mildew and rose trees
Also called white powder disease, powdery mildew is a fungus that develops a layer of white velvety powder that covers leaves and stems.
It develops particularly fast when weather conditions are hot and humid.
Months that are most favorable to it are April or May, when temperatures rise and the air is still full of moisture from the wet months of March and April.
It also makes a comeback at the beginning of fall, when nights grow longer and moisture once again increases.
- Ensure proper air circulation among your rose trees to avoid stagnating moisture.
- Powdery mildew spreads when rose trees are planted too close together, and/or when leaves have trouble finding air…
- Remove infected portions immediately.
- Burn diseased leaves and plant parts.
- Avoid overwatering.
- Eventually, spray with fungicides.
- Milk. Mix ½ quart (½ liter) milk to 4½ quarts (4½ liter) water (total 5 quarts (5 liters)), spray every week until the disease is wiped out!
Black spots on rose tree leaves, Marssonina or black spot disease
Leaves turn yellow and black spots and then black stains appear on all the leaves.
Just like most other fungus, heat and moisture combined increase its spread.
- As soon as the disease appears, remove and eliminate all diseased parts.
- If infected portions remain, the disease can carry over from one year to the next.
- Also clean all your pruning utensils (hand pruner, pruners, etc…) that you have used on your diseased rose tree.
- Do not wet the leaves.
- Spray fermented stinging nettle or horsetail tea.
- Also spray Bordeaux mixture as a preventive treatment as soon as buds start opening, and repeat whenever heat and moisture combine.
Note that today, some rose tree varieties are immune to black spot disease.
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Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Disease on rose tree by Scot Nelson under Public Domain
Aphids on rose tree sprout by Rosalyn & Gaspard Lorthiois, own work
Rose tree Black spot by Rosalyn & Gaspard Lorthiois, own work