Leaves are much more than just a decorative accessory for a magnificent rose blossom. The leaves have the vital task of keeping the metabolism going by means of photosynthesis. To do this, the rose petals remove the carbon dioxide from the air and capture the sunlight so that, in combination with water, glucose forms as an energy supplier for the royal flowers. However, if yellow leaves and brown spots develop, this finely balanced process gets out of hand and there is a risk of total failure for the rose. Read here what really helps now.

Characteristics

  • Plant family of the rose family (Rosaceae)
  • Genus with 100 to 250 rose species
  • Deciduous flowering shrubs
  • Typical features: spikes and rose hips
  • Single, fivefold, semi-double or full double flowers
  • Alternate leaves, mainly in the 2/5 position
  • Terminal or lateral flowers, flowering once or more
  • Horticultural subdivision into wild roses and hybrid tea roses

The majority of the roses cultivated in the ornamental garden are sensitive breeding roses that have been grafted onto the robust rootstock of a wild rose.

Cause: Downy mildew (Peronospora sparsa)

When summer brings cool, damp weather, roses are threatened by the fungal infection downy mildew. Symptoms are dark purple spots on the upper side of the leaves, which turn reddish brown. In addition, the entire leaf turns yellow and dies. If the air humidity is high at the same time, a grey-white, flaky spore coating develops, similar to powdery mildew. However, downy mildew poses a higher risk potential, since the pathogens penetrate deep into the tissue of leaves and shoots, which makes control more difficult.

Control by fungicides

With rose downy mildew, you are faced with the worst leaf fungus that can plague the ornamental garden. Where the pathogens have struck, biological control agents are lost. Therefore, act consistently at the first symptoms. The infected foliage is liberally pruned and destroyed. Then treat the rose with a fungicide approved for the home garden, such as Polyram Garten-Pilzfrei from Dr. steel. To prevent downy mildew from spreading further in the rose bed, treat the neighboring flowers with preparations specially developed for this purpose, such as Neudo-Vital rose spray, an organic-mineral tonic.

Tip: Roses develop a natural defense against pathogens and pests if you refrain from fertilizing with an emphasis on nitrogen. In addition, the location should be sunny and air-flushed so that moisture dries off quickly. A sufficiently large planting distance prevents the flowers from touching to prevent contamination.

Bear: Sternrußtau (Marssonina rosea)

An insidious pathogen that causes yellow leaves and brown spots on roses affects the plants from the end of May without showing any external symptoms. Older, weakened foliage near the ground becomes infected internally. If round brown spots develop on the upper side of the leaves, the disease is already well advanced. Over time, the leaves will turn yellow and fall off. Since the rose is now weakened in its entirety, the young foliage and shoots are not spared from the fungal spores. In late summer and autumn, soot dew then rages particularly intensively in the rose bed and considerably weakens the frost hardiness of the ornamental flowers.

Combined package of measures of control and prevention

When the first brown spots appear, all affected leaves should be cut off and destroyed. If blackspot has already spread extensively, you will hardly be spared the use of a fungicide. Currently permitted preparations are Baymat Rosen-fungusfrei from Bayer Garten or Ortiva Spezial-fungusfrei from Compo. The database of the Federal Office of Consumer Protection and Food Safety publishes a detailed overview of all approved plant protection products. If the infection with blackspot is limited to the older leaves near the ground, the following package of measures will make an effective contribution to control and prevention in the immediate vicinity:

  • Measure the pH value to work rock dust or algae dust into the soil if there is a lack of lime
  • Strengthen all roses in the garden with Neudovital rose spray
  • Water regularly with nettle manure and horsetail broth
  • Weed and loosen the soil several times a week to allow air to reach the roots
  • Cut back at the end of April at the earliest when there is no longer any threat of ground frost
  • Do not water roses overhead
  • Do not administer nitrogen-rich fertilizer
  • Mulch with potassium-rich comfrey leaves

If in doubt, subject the site conditions to a thorough examination. In cool, shady locations with wet, compacted soil, all control and prevention methods are in vain. Don’t wait for brown spots and yellow leaves to appear, but transplant the rose to a sunny, warm and airy spot.

Tip: Organic gardeners swear by the baking soda solution as a preventative home remedy for all kinds of fungal infections on roses. From the beginning of sprouting, spray the ornamental plants every 2 weeks with a mixture of 10 liters of water and 50 grams of baking soda, use natural means to slam the door in the face of advancing fungal spores.

Ursache: Spinnmilben (Tetranychus urticae u. a.)

If roses develop yellow leaves and brown spots in covered locations, such as balconies and terraces, spider mites are among the first suspects. The tiny pests prefer dry, warm microclimates to spread explosively. The extreme sucking activity begins on the underside of the leaf and causes yellow and brown speckles in the first phase. As a result, the foliage yellows and falls to the ground. Typically, the affected rose petals are covered with delicate webs.

Relocation, potash soap solution, organic insecticide, beneficial insects

In the first step of combating the spider mites, their environment is made as uncomfortable as possible. Since the occurrence of these pests is always a location problem, we recommend moving out of the shelter of a canopy. For roses in tubs, this requirement can easily be solved by moving them. For roses in the garden soil, it is worth the effort of transplanting, because the pests will return every year. Proceed as follows:

  • Cut off affected leaves and dispose of with household waste
  • Spray the rose every 2-3 days with a mix of 1 liter of water and 15 ml of potash soap
  • In the case of severe infestation, use commercially available organic insecticide

If fungal infections are spreading in the garden at the same time, spraying rose petals should be avoided. In this case, dried fronds of bracken (Pteridium aquilinum) kill the spider mites. Crushed to a fine powder, the poisonous bracken is applied to the rose petals. Please note that bracken is also not beneficial to human health and wear gloves and a respirator.

If you cultivate your roses in a greenhouse or conservatory, beneficial insects will help you in the fight against spider mites. The predatory mites Phytoseiulus persimilis and Amblyseius californicus take care of the eggs and larvae, stopping the pests from reproducing. The black globe ladybird (Stethorus punctillum) has the adult spider mites at the top of its menu and complements itself perfectly with the predatory mites. The beneficial insects are available from specialist retailers if they are to be used behind glass. After the work is done, they migrate back to look for new grazing grounds.

Tip: A sprouting spray with a neem oil preparation makes a valuable contribution to preventing spider mites and other pests that cause yellow leaves and brown spots on roses. Apply remedies such as Neem Plus Schädlingsfrei at the beginning of May when the shoots have reached 5-10 cm.

Cause: iron deficiency

If the young leaves on roses turn yellow, interspersed with green leaf veins in a herringbone pattern, the ornamental plant suffers from iron deficiency. As a natural trace element, iron is involved in photosynthesis and contributes significantly to the deep green color of the leaves. In normal garden soil, there is enough iron to be taken up by the roses through their roots. If it is primarily the young rose petals that turn yellow, followed by the older foliage, there is an immediate need for action.

Improve PH value, administer iron fertilizer

If you were able to diagnose iron deficiency as the trigger for yellow leaves, the pH value of the soil comes into focus. Although there is a sufficient supply of the trace element in the soil, it is fixed as a result of an excess of lime. Purchase a test set from a garden center or DIY store, which you can use to determine the pH value without any prior knowledge. If the result is significantly above the ideal value of 5.5 to 6.5, the irrigation water is too calcareous. From now on, water with soft rainwater or at least alternately with tap water. If you have previously fertilized with lime, discontinue this care measure. An iron chelate fertilizer such as Fetrilon or Basafer Plus from Compo provides a short-term remedy.

So that yellow leaves no longer appear as a result of iron deficiency in the long term, the soil is optimized with bog bed soil or peat. A mulch layer of comfrey leaves and stinging nettles or bark humus balances acidity and draws iron from deeper soil layers.

Conclusion
Yellow leaves and brown spots on roses are not to be taken lightly. Where these damage patterns develop, the royal flowers are threatened. The art of gardening consists in determining the cause and initiating adequate countermeasures. The most common triggers presented here can be remedied in the early stages with natural means, modified care or a change of location. Where biological control fails, there is a wide range of effective preparations available from specialist retailers to help the plagued rose.

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