Hollyhocks (Alcea), the beauty from the Orient, have also become at home in many gardens in this country. Its flowers in the most beautiful colors from white to yellow, pink, red to dark violet shine from July until late October. Due to their size, the decorative plants are visible from afar. Although the hollyhock is easy to care for and very robust, it can also be attacked by various diseases and pests.

Largely resistant to diseases

As a rule, hollyhocks are very easy to care for and resistant to diseases and pest infestation. In a sunny, slightly damp location with fresh and nutrient-rich soil and a sufficiently large planting distance, diseases and pests have a hard time settling. In addition, proper care with regard to a sufficient supply of nutrients and water is also important. But one or the other disease in the hollyhocks can affect the growth and bloom. It is therefore important to recognize even the smallest damage to the Alcea early on in order to avert greater damage to the plant. The most important diseases and pests are listed below.

mallow rust

Björn S… , Puccinia malvacearum on Marsh-Mallow - Althaea cf. officinalis (30709427647), crop from Plantopedia, CC BY-SA 2.0

Mallow rust is widespread and can cause great damage to hollyhocks and other plants if left untreated. This is a fungal disease with Puccinia malvacearum, which can occur in early spring. The symptoms are expressed as follows

  • yellow-red pustules on the underside of the leaf
  • contain spores of the fungus
  • yellow-brown spots
  • may also appear on petioles and stems

As the disease progresses, the leaf tissue of the hollyhocks initially turns yellow and later turns brown. The leaves begin to wither and eventually fall off. One reason for the development of the fungal disease is the warm, humid weather that prevails over a longer period of time in summer. In addition, the disease is also favored by

  • too small planting distance
  • very high humidity
  • low air circulation between the plants
  • Leaves cannot dry properly

To combat it, biological home remedies should be used as a priority, for example

  • Broth from compost
  • onion broth
  • garlic tea
  • Tansy, horsetail and yarrow broths

Affected leaves should be removed regularly and disposed of in the trash, never in the compost. There is a risk of further spread here. However, if all parts of the plant are affected, the only thing that helps is to completely dig them up and the roots. Disposal then also takes place in the residual waste or is incinerated.

Preventive measures are also important to avoid mallow rust

  • Avoiding waterlogging
  • regular loosening of the soil
  • adequate potassium fertilization
  • use of rhubarb broth
  • Minimum planting distance 50 centimeters
  • sunny, moderately dry location
  • water from below

Notice: The mallow rust fungus can hibernate in the plant as well as in the soil and break out in spring under favorable conditions.

wilt disease (phoma)

Wilt disease (Phoma) on sunflower. Source: Howard F. Schwartz, Phoma macdonaldii on sunflower plant - 3, crop from Plantopedia, CC BY 3.0

Here, too, the cause of this disease is a fungus that damages the inner vessels of the hollyhocks, thereby affecting the water balance of the plant. It is no longer able to supply all parts of the plant with sufficient water. It slowly begins to wither and eventually dies. First signs are

  • brown spots on leaf edges
  • slowly cover the entire leaf
  • Spots turn black
  • contain spores of the fungus

When infested, the hollyhocks wither from below. The oldest leaves are always attacked first. As a rule, infected plants can hardly be saved. In the event of an infestation, care must be taken not to infect other plants. solution to the problem

  • complete removal of the affected plant
  • complete excavation of the root with soil
  • Exchange of soil around the plant
  • Fungal spores overwinter in the soil
  • Disposal in residual waste
  • not on compost - danger of spreading
  • Watering always from below
  • Minimum planting distance 50 centimeters
  • fertilize with a focus on potash
  • regular soil loosening

mallow flea beetle

gailhampshire from Cradley, Malvern, U.K., Mallow Flea Beetle. Podagrica fuscicornisAlticinae . Chrysomelidae - Flickr - gailhampshire, crop from Plantopedia, CC BY 2.0

The beetle (Podagrica fuscicomis), also known as the mallow flea beetle, is not directly a disease but a pest, but can also severely affect hollyhocks. It lays its eggs in the stems of plants. From there, the brownish-blue hairy larvae eat their way into the marrow or root. Eventually they migrate underground to overwinter. One of the most common causes of flea beetles is soil that is too dry. The beetle reaches a size between three and six millimeters. are characteristic

  • blue-green to black in color and
  • yellow-red head and legs

The first signs of the presence of the beetle are expressed as follows

  • Occurs May to June
  • sieve-like perforations in the leaves
  • so-called skeletal damage
  • often only leaf veins remain
  • Infestation of buds and flowers is also possible

The plants must then be treated immediately, otherwise the entire plant population can quickly become infected. First measures should be

  • Dispose of infested leaves in the trash
  • not on compost - danger of spreading
  • Collect the beetles
  • regular loosening of the earth
  • water regularly
  • Do not wet leaves

Notice: Many hobby gardeners swear by the use of matches. These are put into the ground around the plant with the head.

aphids

These pests mainly appear in the spring. They are then numerous on fresh shoots. The aphids (Aphidoidea) can grow up to seven millimeters in size. Typical is the existing proboscis with which they suck the plant sap from their victims. Most of this juice is then excreted as a sticky liquid called honeydew. This covers buds, flowers and leaves and attracts insects such as ants. Hollyhocks, like other plants, are then particularly susceptible to diseases such as sooty mildew. Treatment must be carried out immediately after the appearance of the aphids, otherwise the plants will be seriously damaged.

One solution could be the use of natural predators such as ladybugs, parasitic wasp larvae or hoverfly larvae. Good results can also be achieved by spraying stinging nettle decoction or a lye of curd soap and water. Application in the morning brings the best effect.

snails

Snails (Gastropoda) can also become a dangerous plague for hollyhocks. They prefer to eat the tender, young leaves in the spring after they have sprouted and thus hinder the growth of the plants. Control must take place as soon as the first feeding damage occurs, otherwise the plants can hardly be saved. Measures can be

  • collecting the snails in the evening
  • Application of slug pellets
  • Be careful with pets and children
  • alternatively erection of snail barriers

Sawdust, sand or coffee grounds are ideal for this. These materials are simply scattered around the plants. Coffee grounds are also a good fertilizer.

mallow shrew

Tobias 67, Rhopalapion longirostre TP01, crop from Plantopedia, CC BY-SA 4.0

It can quickly be assumed that this is a mouse, but completely wrong. The mallow shrew (Rhopalapion longirostre) is a beetle. Its pointed trunk is responsible for its naming. Without a trunk, it grows to between 2 and 3 millimeters in size

  • black with dense greyish-white hairs
  • Legs reddish yellow
  • Body length proboscis

The females lay the eggs on the stems and mainly in the flowers between June and July. The hatched larvae then bore deep into the ovary. As a result, the buds dry up. But an infestation is not only recognizable by this, but also by

  • eaten shoot tips
  • dried flower buds
  • Feeding damage to leaves

In the event of an infestation, few flowers can be expected. Treatment is then necessary. To do this, the eggs and beetles must be collected regularly and affected and dried-up parts of the plant must be removed.

Notice: It is not only important to fight the disease or pests on the hollyhocks, but the cause must be identified and eliminated.

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Garden plants