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The genus of hollyhocks not only convinces gardeners and flower lovers with over 60 species. Each one of them also comes up with a lush, almost impressive bloom. However, it is also repeatedly attacked by pests and thus threatens gardening pleasure. But those who know the pests are able to recognize and fight an infestation.
Typical pests on Alcea
Although they are considered to be very robust and easy to care for, hollyhocks suffer from various pest infestations. On the one hand, this includes classic parasites, i.e. insects, etc. In addition, pathogens and fungi exploit the weaknesses of the plant to nest there.
aphids
Although they are not a specific pest of hollyhocks, they sometimes appear in droves, especially in spring - the aphids. They particularly like to attack the young shoots that are developing, as they can easily get to the coveted plant sap here. But even older shoots are not scorned as the population grows.
recognizable signs
- Dark spots as feeding spots on the leaves
- In the case of intensive infestation, the damaged leaves will wilt and dry up
- Sticky secretions of the aphids on the leaves, easily recognizable as a reflection in the light
root cause
- Aphid infestation on neighboring plants - regardless of the species
- Small planting distances for easy propagation from plant to plant
- Young shoots as a rich source of food
- Lack of natural predators that prevent spread in the early stages
Possible solution
- Soapy water or stinging nettle as spray
- Settlement of natural predators such as ladybugs and parasitic wasps
- Elimination of nests of ants as beneficiaries and even caretakers of lice
- use of pesticides
NOTICE: Although chemical preparations should only be used as a last resort for ecological reasons, it is worth resorting to chemicals when hollyhocks are in bloom. Because the sensitive flowers are usually affected by pouring liquid manure or soapy water over them. Ultimately, a damage is then only replaced by another damage.
mallow flea
Despite its misleading name, the mallow flea beetle (Podagrica fuscicornis) is biologically a beetle. Since hollyhocks belong to the mallow family, this pest finds an ideal food base here. Both real damage and purely visual impairments can - depending on the intensity of the infestation - be the result of its presence.
gailhampshire from Cradley, Malvern, U.K., Mallow Flea Beetle. Podagrica fuscicornisAlticinae . Chrysomelidae - Flickr - gailhampshire, crop from Plantopedia, CC BY 2.0
recognizable signs
- Numerous small feeding holes distributed over the leaf surface
- At the same time no impairment of the leaf veins
- Recognizable animals are green, blue, or black in color with red legs; Body size a few millimeters
cause of infestation
- Warm, humid weather as ideal breeding conditions for the animals
- Small planting distances as an ideal prerequisite for rapid spread from plant to plant
- Particularly high probability of infestation in monocultures
Possible solution
- collect
- Loosen the soil regularly to make access for animals more difficult
- Stick matches around the plant with the head in the ground
- Nettle manure or soapy water as a spray
- Increase plant spacing
- Interplant other plant species not susceptible to the mallow flea beetle to prevent spread
- insecticides
mallow shrew
The mallow shrew (Rhopalapion longirostre) is not a rodent either, but also a beetle. It owes its name to its pointed snout, while otherwise it comes close to numerous other plant pests that are typical of the species. Another connection to its name can be derived with a little imagination from the recognizable image of damage. The mallow shrew prefers to attack the tips of the shoots, so that the striking result is a significantly reduced number of flowers.
Tobias 67, Rhopalapion longirostre TP01, crop from Plantopedia, CC BY-SA 4.0
recognizable signs
- Bare, dying shoot tips
- Small, translucent greenish eggs on stems
- One to three millimeters in size, roundish-compact beetles with grey-black coloring and brown-grey legs, characteristic pointed proboscis
cause of infestation
- Drive out in the spring as an attractive source of food for the animals
- Promotion of infestation through high planting density and uniform plant species
Possible solution
- Collecting eggs and beetles
- Nettle manure or soapy water as a spray
- Increase in biodiversity and planting distances
- use of pesticides
mallow rust
Not real pests, but still a real danger for hollyhocks are the pathogens of mallow rust (Puccinia malvacearum). Every year the fungal disease threatens the stocks and quickly turns the decorative plants into unsightly remnants.
Björn S… , Puccinia malvacearum on Marsh-Mallow - Althaea cf. officinalis (45599812022), crop from Plantopedia, CC BY-SA 2.0
recognizable signs
- Small-sized, yellow spots on the upper side of the leaf
- Red-brown pustules on the underside of the leaf
- Occurs in early spring on the first young shoots
cause of infestation
- Warm, humid weather is the ideal precondition for propagation
- Poor ventilation or too dense planting as a cause of insufficient ventilation of moisture
- Planting distance too small for rapid transfer from plant to plant
Possible solution
- use of fungicides
- Remove and dispose of infected shoots immediately
- After infestation, remove and destroy the plant in autumn except for the stalk because the mycelium overwinters on the hollyhocks, also treat the stalk and soil with a fungicide
- Prevention by using yarrow or horsetail brew as fertilizer
ATTENTION: In the case of fungal diseases, removed plant parts should not end up in the compost, as the fungus will continue to multiply there and infect new plants from there. Either the dry shoots or plants should be burned or disposed of with household waste.
snails
Wherever tender young shoots beckon, snails are not far away. In addition to numerous other plants, they also like to feast on the representatives of the Alcea. They usually suffer from a heavier infestation than other plants, since the comparatively thin plant skin and the high sap content of the leaves make them a particularly worthwhile target. Once the leaves have been eaten away, the plant quickly suffers from a lack of supply. The consequences can be inhibited growth or complete death.
recognizable signs
- Large format feeding marks or completely eaten leaves
- Clearly recognizable, shiny, iridescent traces of snail slime
- Easily recognizable representatives of different house and slug species
cause of infestation
- Spring sprout as optimal food supply
- Lack of other feed alternatives
- Absence of predators as a natural way of combating the spread that is getting out of hand
Possible solution
- Snail barriers made of metal or plastic
- Natural alternatives made from coffee grounds or sand
- Sawdust as an insurmountable obstacle on the floor (sucks up slime secretion)
- collect snails
- Set up beer traps
- Use of slug pellets (not for pets or children in the garden)
TIP: Get to grips with the snails, especially in the evening hours, as the animals then leave their daytime hiding places and go in search of food!
wilt
Wilt disease originates from a fungus of the genus Verticillium. As the name suggests, an infestation by this pest causes the hollyhock to wilt. This happens after implantation in the root area, starting from the bottom up. Since the fungus also damages the inner pathways for the plant sap, an untreated disease quickly leads to total loss.
Howard F. Schwartz, Verticillium wilt dahliae, crop from Plantopedia, CC BY 3.0
recognizable signs
- Withering from the base of the stem
- No clearly recognizable expression of the mycelium
cause of infestation
- Warm, humid weather as a good basis for propagation
- Small planting distance with poor ventilation
- Monoculture as an ideal basis for distribution
Possible solution
- Immediate removal of infested perennials
- Replacement of the soil in the root area after removing the perennial
- Use of fungicides, but only moderate success here
- Increasing the plant spacing for better ventilation and further path to the new host