It is not without reason that the rose is called the “queen of flowers” by many and should not be missing in any ornamental garden. Unfortunately, the beauties are very susceptible to diseases, especially fungal infections such as powdery mildew. Read what you can do against this common pathogen.
Powdery or downy mildew on roses?
No question: As soon as the leaves and shoots of your roses show the first signs of powdery mildew infestation, you of course want to treat the disease immediately. However, it is important to first make an accurate diagnosis. Mildew is by no means the same as mildew, as there are a whole range of different fungal pathogens. Depending on whether it is powdery mildew or downy mildew, you must also choose the appropriate treatment. What works against powdery mildew is not necessarily suitable against the downy mildew.
The following table shows you how to best distinguish between the different types of mildew and what remedies can help against it.
| Powdery mildew | Downy mildew | |
|---|---|---|
| pathogen | Ascomycetes (Erysiphaceae) | Oggushrooms (Peronosporaceae) |
| How to recognize an infestation | white, flour-like and wipeable coating or spots on the tops of leaves, stems and shoot tips, can also appear on flowers and buds | white to gray coating on the underside of the leaf, can also be velvety brown |
| Damage as the disease progresses | Plant parts turn brown, dry out and fall off. | Plant parts turn brown, yellow or purple. |
| Occurs under these conditions | Fair weather fungus: occurs in dry weather with temperatures between 20 and 25 °C, morning dew is dangerous, transmission by insects and wind is possible | Bad weather fungus: occurs in damp weather with temperatures between 15 and 20 °C or in high humidity (e.g. in a greenhouse) |
| Best antidotes | Spray with horsetail extract, garlic | Spraying with tansy infusion, oregano, savory |
Causes of Mildew
Incorrect care or weather changes promote mildew
Mildew mainly occurs as a result of strong weather fluctuations (mainly in spring) or because the roses have not been properly cared for. Above all, planting too closely, incorrect watering over the leaves and fertilizing with a high nitrogen content promote fungal diseases. Check your rose plants regularly for signs of infestation so that you can act immediately at the first symptoms. Mildew spreads very quickly and is more difficult to control the more severe the symptoms.
Mildew on roses – what to do?
You can find out how to plant and care for roses correctly and thus keep mildew and other rose diseases away in this informative article:
video: Youtube
The only way you can protect yourself against mildew on roses is by taking suitable precautionary measures, which we will introduce to you further down in this text. If these don't help, try some tried-and-tested home remedies first. These include a whole milk and water mixture or a baking soda-based spray, both of which are slightly acidic and affect the spread of the fungi. There are also other very good sprays that you can make from ingredients you have collected yourself.
However, cutting back affected plant parts is fundamental to the success of the measures. Leaves and shoots that are already discolored no longer have a he althy color, which is why only generous pruning helps in the case of a severe infestation. Slightly infected roses, on the other hand, can be treated by wiping the affected leaves with a milk mixture, providing the plants with a strengthening agent and, if necessary, improving the site conditions and care.
Known home remedies for mildew on roses
There are many good home remedies for mildew on roses
The two home remedies listed here are proven classics that help against both powdery mildew and downy mildew. It is important not to carry out the injections once, but rather several times at intervals of a few days over a period of at least two to three weeks. Also make sure that you can dry the rose petals and shoots quickly afterwards. It is therefore best to carry out the spraying in the late morning and in dry weather.
Whole milk-water mixture for spritzing
The well-known milk-water mixture, which you can use to treat your roses as a preventive measure from the beginning of the growing season, has proven particularly effective in cases of initial to mild mildew infestation. The recipe is as follows:
- If possible, use untreated whole milk (at least 3.5 percent fat).
- Alternatively, you can also use buttermilk.
- Mix the milk with boiled and cooled water in a ratio of 1:9.
- It is best to use rainwater or well-stale tap water.
- Pour the mixture into a clean and disinfected spray bottle.
- Spray the roses affected by powdery mildew so heavily that the spray drips from the leaves and shoots.
- Don't forget to treat the undersides of the leaves.
- Repeat the treatment several times a week.
Baking powder mixture
Baking powder works even better than spraying with a milk-water mixture. However, don't choose just any baking powder, choose one with baking soda. Mix a packet of this with two liters of water and 20 milliliters of neutral cooking oil (e.g. rapeseed or sunflower oil) and fill the mixture into a spray bottle. Treat the parts of the plant affected by powdery mildew several times a week.
Make your own sprays against mildew on roses
In general, chemical sprays are rarely actually necessary in hobby gardens. After all, there are enough effective substances in nature that can be produced inexpensively and easily. If you would rather buy a ready-made product, you can use the biological preparation “fungus-free (€11.00 on Amazon)”.
Horsetail against powdery mildew
An effective manure against powdery mildew can be made from field horsetail
Field horsetail grows almost everywhere and is often viewed as a weed and is plucked out. Manure made from the herb not only has a very stimulating effect on roses and is very effective at preventing infection with powdery mildew. You can use horsetail broth - diluted with water in a ratio of 1:10 - both as a prevention and for treatment in the early stages of mildew. The effect is based on mineral s alts such as silica, potassium and calcium, which make roses and other plants more resistant to powdery mildew.
Recipe for horsetail manure
- Collect one kilogram of field horsetail without roots. Alternatively, you can also use swamp horsetail.
- Chop up the plant parts.
- Put the plant material in a plastic bucket.
- Pour ten liters of cold water.
- Rainwater is best.
- Add a handful of primary rock powder.
- Stir well.
- Let the mixture stand covered with a jute cloth or a piece of wire mesh for about 14 days.
- Stir twice a day.
The manure is ready as soon as there are no more bubbles rising. Now you can filter the liquid and fill it into canisters. Between April and August, spray your roses dripping wet with the product about every eight to ten days.
Garlic against powdery mildew
A garlic extract has also proven to be an effective remedy against powdery mildew. Spray the affected plant parts with the product diluted with water in a ratio of 1:10 or 1:20 (depending on the severity of the infestation), preferably in the evening. Repeat the application regularly.
Garlic extract recipe
- Crush 100 grams of garlic including the peel.
- Mix the garlic with three tablespoons of rapeseed oil.
- Let the mixture stand covered for 24 hours.
- Now crush the garlic and strain the liquid.
- Add a tablespoon of liquid dish soap.
- Stir the mixture well.
- Finally, pour a liter of water into the mixture.
Refrigerated and protected from the sun, this preparation lasts about three weeks.
tansy against downy mildew
The flowers of the tansy are an efficient natural remedy against mildew
The intensely yellow blooming tansy - often found in the summer months, especially on the edges of fields and paths - makes a great spray against downy mildew when used as an infusion. To do this, pour one liter of hot, but no longer boiling, water over 100 grams of fresh or 20 grams of dried flowers. Let the brew steep until it has cooled to room temperature and then strain it. Dilute the product in a ratio of 1:5 with water and spray affected parts of the plant with it.
Tip
In contrast to manures and extracts, infusions do not have a shelf life and must be used immediately.
Oregano or savory against downy mildew
Extracts from savory or oregano are hardly known, but are also very effective against downy mildew. Both herbs contain essential oils that are resistant to fungal pathogens. To make such a fungicide, you also need extra-fine clay so that the active ingredients stick better to the rose petals.
Recipe for a fungicide based on savory or oregano
- Chop 100 grams of fresh herb.
- Mix this with a tablespoon of rapeseed oil.
- Let the mixture stand for 24 hours.
- Then carefully strain the escaping liquid.
- Mix this with three to four drops of liquid dish soap.
- Now mix the mixture with 250 milliliters of water.
- The liquid should be homogeneous.
- Now make a clay-water mixture from a teaspoon of clay and a liter of rainwater.
- Pour both liquids into a spray bottle and shake well.
You can use this spray as needed.
Excursus
Cutting roses correctly
Regular pruning makes roses more resistant to mildew. On the one hand, with an annual spring pruning you cut away any overwintering fungal spores, on the other hand, the rose is airier thanks to the pruning and is therefore less endangered per se. How, how much and when you cut depends on the rose variety and its classification.
How to effectively prevent powdery mildew on roses
“For roses to stay he althy, they absolutely need an optimal location!”
However, the most effective method against all types of mildew is and remains careful prevention. You should heed the following tips:
- Roses need a light and airy location.
- Do not plant them too closely, but keep the recommended planting distance.
- The shrubs also feel most comfortable on moist and nutrient-rich soil.
- Keep the rose bed free of weeds, as many weeds attract and spread fungal diseases.
- Mulch the root area of the roses with bark mulch.
- Always water roses from below and directly onto the ground, never over the leaves!
- Watering preferably in the morning, as evening watering promotes the development of fungal diseases.
Evening watering also has another disadvantage, as it attracts voracious slugs.
Excursus
Plant a protective barrier against mildew
Some herbs are resistant to mildew, which is why you should plant them in the rose bed: chervil, chives, basil and garlic practically act as a natural protective barrier, as does foxglove.
These rose varieties are resistant to mildew
The word “resistant” implies that the rose varieties labeled in this way cannot suffer from fungal diseases such as powdery mildew. This is of course nonsense, as even plants that are particularly robust against pathogens can become infected - for example because the site conditions are not right (e.g. the roses are planted too closely) or they have been watered incorrectly / heavily fertilized. Such conditions weaken even more robust varieties over time, making them more vulnerable.
Weather influences the occurrence of rose diseases
In addition to an unsuitable location or incorrect care, the weather can also trigger fungal diseases - for example if the year was particularly wet. In a year in which a lot of fungi thrive, mildew fungi naturally also thrive. Nevertheless, planting a rose variety that is resistant to powdery mildew makes sense because it is significantly less susceptible than many other varieties - provided, of course, that the location and care conditions are right.
Choose robust ADR roses
If you want to be on the safe side, choose a so-called ADR rose if possible. These are varieties that have to go through a “rose TÜV” test and meet strict criteria before they are awarded the test seal. These test criteria not only include external factors such as growth and flowering, but also susceptibility to typical rose diseases or winter hardiness. Basically, ADR roses are very robust and not very susceptible to powdery mildew, but are by no means completely immune to disease.
Tip
ADR roses are a German test seal, which is why most new varieties from abroad - such as the famous English roses - are not tested. However, that doesn't mean they're not very robust - they're just not submitted for consideration.
Frequently asked questions
Does baking soda actually help against mildew on roses?
In fact, baking powder helps very well against mildew - but only if you buy a type with baking soda (sodium bicarbonate). However, most baking powders available in Germany contain other leavening agents and are therefore unsuitable for the purpose of combating mildew. Baking soda is often commercially available under names such as baking soda, caustic soda or baking soda.
Is powdery mildew contagious to other plants?
Since mildew - regardless of whether it is the "real" or the "false" one - is a fungus, the disease is highly contagious. If a rose is already infected by the fungal lawn, the pathogen spreads from it to other roses and other ornamental and useful plants. This is why it is so important to act quickly and, if possible, isolate the affected plant. Furthermore, plant parts infected with mildew do not belong in the compost, as the spores survive and infect other plants when the finished compost is spread.
Is mildew actually poisonous?
Both powdery mildew and downy mildew are poisonous. People who are allergic to mushrooms or penicillin are particularly at risk. These people can suffer severe allergic symptoms, including allergic shock, from contact with the mildew fungus. As an allergy sufferer, you should avoid touching infected plants without protection (gloves, respiratory protection if necessary). Also, do not eat contaminated plant parts, this can lead to problems in the gastrointestinal tract.
What does mildew tolerant mean?
Mildew-tolerant rose varieties are less susceptible to infection with the fungal pathogens that cause them. However, if the conditions are right, the variety in question can still become diseased. Only mildew-resistant roses do not suffer from mildew.
Tip
Remove dried or damaged plant parts as quickly as possible, as these provide perfect entry points for fungal pathogens. Garden tools used to cut roses (e.g. scissors) should also be cleaned and, if necessary, disinfected before and after each use.