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From August, the blackberry bushes full of black, juicy fruits hang along the edges of paths and in numerous gardens. Sometimes, however, the hoped-for harvest is endangered, because even the robust blackberries are not immune to diseases. Thornless varieties are particularly affected, but old varieties are also occasionally affected. In this article we explain which 7 infections are particularly common and how you can recognize and treat them.

blackberry rust

Blackberry rust is a problem, especially with the thornless new breeds. The fungus Phragmidium violaceum causes this fairly common disease, which usually appears from the end of June / beginning of July. But even if you don't see any symptoms yet, your blackberries may already be infected: the fungus overwinters in the fallen leaves and on the leaves that remain on the tendrils. From here he infects the new leaves that sprout in the spring.

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You can recognize blackberry rust by these characteristic symptoms:

Source: Björn S… , Phragmidium violaceum on Blackberry - Rubus fruticosus agg. (42411154342), Edited by Plantopedia, CC BY-SA 2.0
  • violet to reddish spots on the upper side of the leaf
  • later formation of orange-red spore deposits on the undersides of the leaves
  • turn brown to black over time

Without treatment, the fungus does not go away, but instead re-infects the blackberries every year.

control and prevention

Blackberry rust is one of the more harmless diseases, because the harvest is only at risk if the infestation is severe. Therefore, do not immediately resort to chemical pesticides, but try these methods first:

  • Remove infested leaves from the bush or collect them from the ground
  • never throw it in the compost
  • Spores survive there and cause re-infection the next year
  • Dispose of infected foliage in household waste or by incineration

The disease can be prevented quite well by a regular thinning cut in summer. In addition, you should only use nitrogenous fertilizers very sparingly, as this makes the blackberries more sensitive to fungal infections.

Tip: If you want to avoid blackberry rust, you can also plant resistant varieties such as the thornless 'Arapaho'. The 'Thornless Evergreen' variety, on the other hand, is particularly susceptible.

Colletotrichum fruit rot

Colletotrichum fruit rot, which is caused by fungi of the species Glomerella cingulata, is more problematic for a rich blackberry harvest. This wilt disease is also known as anthracnose and often occurs on currants. Therefore, infection of the blackberry plants from neighboring currant bushes is likely.

Colletotrichum fruit rot occurs in humid and warm weather, so it is not uncommon in summers that are both humid and warm at the same time. The pathogen spreads very quickly and can result in crop failures of up to 30 percent.

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Colletotrichum fruit rot is one of the diseases of blackberries with a characteristic appearance and can therefore be diagnosed even for laypeople. Typical symptoms are:

  • first signs at the beginning of fruit ripening
  • initially affects only individual berries
  • do not first turn red and then black, but milky cloudy
  • small pustules on the surface containing pink spores
  • Affected berries dry up and mummify
  • stick to the bush, do not fall off

If the infestation is severe, the whole plant will suffer, showing, for example, stunted growth and delayed ripening of remaining blackberries.

control and prevention

The disease occurs mainly on late-bearing varieties, so by planting earlier blackberries you can avoid the onset of an eventual infection. You should also avoid a new outbreak of the disease in the following year by consistently removing fruit mummies and cutting back the affected plant vigorously in autumn. The use of chemical pesticides is not necessary.

powdery mildew

Powdery mildew is also a fungal disease. It is caused by fungi from the Erysiphaceae group and occurs on many garden plants, not just blackberries. The disease is nicknamed the "fair-weather fungus" because infection only occurs in warm, dry weather. Temperatures above 24 °C are ideal for spore formation and rapid spread, which is why powdery mildew can mainly be seen in the warm summer months.

Powdery mildew on maple leaf. Source: Jerzy Opioła, Powdery Mildew Acer DK43 (1), crop from Plantopedia, CC BY-SA 4.0

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Initially, the fungus only affects the leaves and appears as a whitish, mealy-looking and easily wipeable coating on the leaf surfaces. Shoots and flower buds can also be affected. In the early stages, powdery mildew can still be treated very well with home remedies. On the other hand, if you intervene too late, the infection affects the entire plant and can even infect neighboring plants. Other symptoms of a fungal infestation also include curled and stunted leaves that eventually fall off.

control and prevention

Fungal diseases such as powdery mildew must be treated as the spores overwinter on the plant, causing a new infection every year. In the long run, this weakens the plants and ensures that growth slows down and fewer and fewer flowers and fruits are formed. Therefore, proceed as described:

  • Cut back affected leaves and other plant parts
  • Do not throw clippings on the compost
  • Disposal via household waste, recycling center or incineration
  • Spray the blackberry plant
  • Use a milk-water mixture (1 part fresh whole milk if possible, 9 parts low-lime water).

Alternatively, you can also spray with baking soda: mix a packet of baking soda (no baking powder!) with one liter of water and 20 milliliters of cooking oil. A squirt of washing-up liquid ensures that the water and oil emulsify together. You can also carry out the spray treatment as a preventative measure on endangered plants (such as those that were already ill the previous year). For this purpose, spray them every two weeks from the moment they sprout in spring.

Tip: While the white fungal coating on the leaves is not poisonous, it can cause allergic reactions in certain people. Patients who have a penicillin allergy or other fungal allergies are particularly at risk. If you are affected, protect yourself by using a respirator and gloves.

Wrong mildew

Downy mildew is also one of the diseases that mainly affect the leaves. It is caused by fungi from the Peronosporaceae group, which are so-called egg fungi. These are most evident in cooler, damp weather as they are transmitted by rain and penetrate the wet blackberry leaves. Here the fungi form further spores that easily infect neighboring plants. Downy mildew occurs mainly in spring and autumn.

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You can easily recognize downy mildew by its characteristic damage pattern:

  • initially white-grey, wipeable coating on the undersides of the leaves
  • appears mealy, but is difficult to wipe off
  • yellow-brown spots on the upper side of the leaves
  • Growth disorders / stunted growth in severe infestation
  • delayed flower and fruit development
  • delayed fruit ripening

Due to its increased occurrence in bad weather, downy mildew is also known as the "bad weather fungus".

control and prevention

Like so many fungal diseases, this pathogen overwinters on the affected plant and infects it again the following spring. To prevent this and further spread, you should take countermeasures immediately:

  • Cut off affected leaves and other parts of the plant
  • do not throw it in the compost, but dispose of it with household waste
  • Spray blackberries with horsetail stock
  • alternatively use garlic stock
  • Repeat application at regular intervals
  • keep it dry as much as possible

Tip: Blackberries and other garden plants are less endangered if you plant them in an airy spot. Regular pruning is also important so that the leaves are not too dense and dry off quickly after a downpour.

gray mold

Source: John Yesberg, SemillonBotrytisCinerea, Adapted from Plantopedia, CC0 1.0

One of the most common blackberry diseases is gray mold, which is caused by the fungus Botrytis cinerea. This primarily affects the berries, which is why it is also called fruit rot. Gray mold fruit rot occurs when the humidity is high (e.g. as a result of a rainy summer) or because the blackberries are too dense and not airy enough.

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The disease manifests itself as a grey, dusty coating on the fruit. They can no longer be eaten or processed. Tendrils and leaves are only affected if the infestation is severe.

control and prevention

Botrytis spores are present in every garden, so infection is likely given the right conditions. Therefore, make sure that the disease does not break out with regular pruning and a suitable location (sunny and airy). Affected plant parts must be cut off and disposed of immediately, but not in the compost. Feel free to cut generously.

vine disease

Among the diseases typical of blackberries is tendril disease. This occurs especially in rainy weather.

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Vine disease is manifested by these symptoms:

  • purple spots on tendrils
  • often with a red border
  • and brownish in the center
  • heavy infestation leads to weakening, stunted growth and death of the plant

This year's - i.e. young - tendrils, which are contaminated with the pathogen Rhabdospora ramealis between April and June, are usually affected by an infection. The disease is particularly common in some regions.

control and prevention

In the event of an infection, generously cut away the affected tendrils and discard the clippings. Here, too, it is important not to throw the parts of the plant contaminated with spores onto the compost, as a renewed infection is then likely. When planting new plants, choose resistant or non-sensitive varieties, such as 'Thornless Evergreen'.

Rubus dive

Rubus disease is not a fungal but a bacterial disease. It is caused by parasitic bacteria called phytoplasma. These are mainly located in the plant roots. The pathogens are transmitted via insects, primarily cicadas. In addition to blackberries, raspberries are also affected by this dangerous disease.

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Typical of this disease are not only the conspicuous deformations of the flowers and fruits, but also the development of numerous small, thin rods from the tendril buds. For this reason, the rubus swine is also referred to as a branching disease or witch's broom.

control and prevention

Control is not possible, instead infested plants must be completely cleared. Above all, remove the roots, as the pathogen is mainly found here. Do not plant any more Rubus species in this spot. In addition to the various types of blackberry and raspberry, these also include cloudberries and tayberries.

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