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Roses used to be considered the flowers of kings. It is not for nothing that they still adorn many a stately ornamental and pleasure garden today. And it is not for nothing that the rose has established itself as one of the ornamental plants par excellence in countless private front and ornamental gardens as an integral part of the summer floral decoration. To ensure that you can enjoy their splendor for as long as possible, the following information on known and recurring diseases and damage patterns will help you to first recognize them and then fight them effectively or even avoid them from the outset.
Typical rose diseases
Although a large number of diseases can occur in individual cases, in the majority of cases the rose is attacked by one of the following typical rose diseases. It is therefore worthwhile to recognize the associated damage pattern and to be able to eliminate the causer in a targeted manner.
Blackspot (Diplocarpon rosae)
symptoms
- irregular grey-black spots of varying size with radiating edges
- in the surrounding area stains mostly yellowish to yellowish-reddish discoloration of the rose petals
causes
- host-specific fungus
- usually affects only rose plants
- spreads especially in damp and cool weather
Follow
- in the case of intensive infestation, early leaf drop already in summer
- Weakening of the entire plant up to the death of young shoots
- then reduced growth performance in the following year
combat
- Use of suitable and approved fungicides as soon as they are first identified
notice: Blackspot is considered the most common of all rose diseases, so it pays to have the right antifungal products on hand in advance so you can use them immediately when needed.
tip: The fungal spores hibernate in dead leaves on the bottom of the bed. In order to avoid fighting again in the following year, fallen leaves should be removed and disposed of. However, composting or mulching the leaves should be avoided at all costs, as the spores survive these processes without any problems and are even more widespread!
Powdery mildew (Sphaerotheca pannosa var. rosae)
symptoms
- whitish, mealy coating on the upper side of leaves, but also on flower stalks, buds and sepals
- Undersides of leaves usually less affected due to less sunlight
causes
- fungal disease
- so-called "fair-weather fungus", which occurs and spreads primarily in warm, muggy weather
- Infestation therefore rarely before June
- mainly occurs on roses that are very well taken care of, since high growth leads to thick, soft leaves that offer little resistance to the fungus
Follow
- Weakening of leaves, flowers and entire plant
- in case of intensive infestation leaf shedding and then reduced growth of the affected areas or the entire rose
combat
- Use of suitable fungicides
- Prevention is also possible with plant strengtheners such as horsetail broth or sulphur-containing pesticides
tip: Fertilizers with a high nitrogen content in particular lead to an increased susceptibility to powdery mildew. Therefore, only use nitrogen in moderation to avoid fighting the disease in the first place
powdery mildew
Rose Rust (Phragmidium mucronatum)
symptoms
- numerous orange to rust-red spots with partly dark borders on the upper side of the rose leaf, merging into one another in the case of intensive infestation
- elongated spore deposits on the underside of the leaf, protruding on the upper side of the leaf in bright red
root cause
- rust fungus
Follow
- in case of severe infestation leaf shedding
- resulting in weakening of the shoot and the entire plant
combat
- Use of suitable fungicides with approval
- In the case of intensive infestation, remove and dispose of infested shoots to prevent the spread of spores
Downy mildew (Peronospora sparsa)
symptoms
- round, violet spots on the upper side of the leaf
- often converging when expanded
- Arranged often along the leaf midrib
- greyish, mold-like coating on the underside of the leaves in autumn
causes
- leaf fungi
- Occurs mainly in cool and damp weather conditions due to water droplet infection
Follow
- affected leaves fall off
- Weakening of the drive for the following year
- if the infestation is severe, the whole plant dies off
combat
- Remove and eliminate affected shoots immediately after detection
- Use appropriate fungicides to prevent spread
danger: Although downy mildew is considered to be one of the most aggressive leaf fungi, the range of approved control agents is severely limited. Only a handful of remedies are currently approved and therefore available for private use.
Bark spot disease (Coniothyrium fuckelii Sacc.)
symptoms
- brown to reddish-purple bark spots on trunk and shoots
- usually starting from shoot buds or bark injuries
- later drying out and tearing open of the affected areas
causes
- fungal disease
- usually appearing on last year's shoots
- favored by a strong nitrogenous fertilization
Follow
- Death of the shoots above the affected area
combat
- Cut off and discard the affected shoots
- ideally by incineration or disposal in residual waste
- when composting or chopping, there is a risk that the spores, which cannot be destroyed in this way, will be passed on
tip: Treatment with fungicides in autumn helps to contain the fungus before the hibernation phase and to prevent a rapid outbreak of the infection in spring.
Common parasites and pests
In addition to illnesses, animal guests also like a rose that is usually well cared for in the home garden and is growing luxuriantly. It is obvious that this does not meet with the approval of hobby gardeners, at least in the case of the following well-known and frequently encountered pests.
Large rose aphid (Macrosiphum rosae)
identifying features
- about 3 to 4 millimeters long, elongated animals with pale green coloring and partially translucent bodies
- mainly found on young shoots, flower buds and leaves
- in the case of intensive infestation in individual cases initially loss of colour
- later, the affected leaves will roll up and fall off
damage picture
- strong impairment of the infested parts of the plant by honeydew excretion of the aphids
Follow
- reduced photosynthetic capacity of the leaves
- consequently poorer supply situation
- in the case of extreme infestation, drying out of leaf parts or whole leaves with premature dropping off
combat
- use of pesticides
- Biological remedy for moderate infestation, for example with nettle manure or a solution of soft soap
Aphid infestation on a rose
tip: Even small aphid populations can be controlled by favoring their natural predators, including, for example, the ladybird, the parasitic wasp and the lacewing. If the rose is grown in the vicinity of host plants or breeding opportunities for these animal species, the aphid problem often resolves itself from the start without the hobby gardener even noticing it.
rose sawfly
identifying features
- in spring they lay eggs on the undersides of leaves
- However, the most striking feature of an infestation is green-yellowish larvae with a strongly incurved abdomen
- Body size up to 10 millimeters
damage picture
- feeding damage
- usually only leaf skeletons are preserved due to so-called window damage
- partially spanned with remaining, translucent skins of the upper or lower sides of the leaves
Follow
- intensive damage to affected shoots
- with severe infestation to the death of the shoots due to insufficient supply
combat
- Control after infestation not possible
- since pesticides are not permitted
- Collecting the caterpillars, on the other hand, is not effective
- effective protection, however, only by covering the plants with insect protection nets
Planthopper (Edwardsiana rosae)
identifying features
- pest about 3 millimeters in size
- Easily recognizable by the accumulation of yellowish-green larvae and adults in groups on the underside of the leaves
- when approaching the plants, the fully grown animals often easily recognizable jumping up
damage picture
- numerous small, mostly round, light green bite marks distributed over the leaves
Follow
- Impairment of the leaf function up to drying out and falling off by sucking out the plant sap
combat
- Settlement of predators such as leaf and predatory beetles and spiders
- Prevention of hibernation by pruning young shoots in autumn, since oviposition takes place in the bark cracks of the young shoots in autumn
prevention
Keep rose diseases out of your own garden from the start
It is true that the selection and effectiveness of chemical agents for eliminating numerous types of damage is enormous. However, the number of diseases against which there is simply no help is at least as large. That's why rose breeders are taking a different approach today, by constantly producing new, ever more resistant species. By selecting the most insensitive varieties possible, breeders and hobby gardeners have the opportunity to avoid numerous diseases from the outset.