If a group of small, beetle-like animals quickly form on mallow plants, they are probably linden bugs (Oxycarenus lavaterae). Find out what you can do about it.
Recognize
In order to know whether it is linden bugs, or mallow bugs, as they are also known, that gather in groups on trees and/or shrubs, they should be identified in advance. This is done by comparing typical optical properties and providing information as to where and when they affect plants.
Optical details:
- Colour: dark reddish, black-red
- Confusion risk: with fire bugs, which are often present at the same time
- Size: four to six centimeters
- Silver shimmering wings
- Larvae: reddish-brown abdomen - black head and breast
- Gather in colonies that grow rapidly
- Often “attached” to bark in mating position
- Likes to lay eggs in crevices in bark
Season for infestation:
- Especially in spring when temperatures are higher after their hibernation, when they are foraging
- Spring to late summer to lay eggs
- Larger masses of linden bugs usually accumulate in autumn because they like to spend the winter in cracks in the bark
- Many die off in winter, others survive hibernation, which lasts until early spring
incident:
- Predominantly only on mallow (Malvaceae) and lime trees (Tiliaceae) such as shrub poplars, marshmallow and hibiscus
- Mostly on new plantings
- Often also on older linden trees
- Especially fond of small-leaved lime (Tilia cordata)
- Often in treetops during the growing season
- More visible from autumn on tree trunks and thick branches
- Can be found on house walls - usually only in search of winter quarters in winter
- Occasionally "get lost" in buildings/living areas
small-leaved lime
damage picture:
- Occasional leaf discolouration due to statements made by the plant sap
- Slight yellowing of unlignified shoots when sucking on them
- In the case of extensive colony formation on branches, these can break off
need for combat
Lime bugs do not need to be combated as they do not pose a life-threatening threat to plants. They do not cause any significant damage, as they feed mainly on the seeds of the mallow and linden plants and extract the juice from them. Likewise, humans have nothing to fear.
Nevertheless, they are not welcome guests in the garden, so many hobby gardeners want to combat them. However, this makes sense in any case, because if other pests join, a significantly more extensive damage pattern can arise and the plants are endangered by less resistance. Accordingly, caution should be exercised here, especially in the event of an infestation with the woolly scale insect (Pulvinaria regalis).
Cup scale insect, Source: Donald Hobern from Copenhagen, Denmark, Pulvinaria regalis (7439920392), Edited by Plantopedia, CC BY 2.0
combat
Although linden bugs are considered harmless, if they are undesirable, here are some control measures:
vacuum cleaner
A vacuum cleaner is a good choice for getting rid of the Oxycarenus lavaterae. It only becomes difficult if they are located high up, where a classic vacuum cleaner cannot reach them. A so-called backpack vacuum cleaner is the solution here, with which a ladder can also be used to get to the top of the crown. It is important that the suction tube is pushed from the bottom up over the bark to achieve a scraping effect so that the pests are loosened and drawn in directly by the suction air. The suction bag must then be closed tightly and disposed of safely with household waste.
soapy water
Soapy water has proven to be a very efficient means of combating various pests for many years. It is also effective against the linden bug, which becomes denatured when it comes into contact with and is absorbed by the soapy water. Preparation and application work as follows:
- Use biodegradable detergent, curd soap or soft soap without additives
- Add about 100 grams/milliliter of soap/detergent to every liter of water
- Let the soap dissolve - mix the washing-up liquid well
- Pour the soapy water into the spray container
- Spray directly on the pests (drip wet)
- In any case, also spray the trunk and ground around the tree (regardless of the presence of mallow bugs)
- Repeat three times, two days apart
- If not all of them have died, start the process again one week after the last application
Tip: Spraying susceptible trees/plants generously with soapy water every spring and fall can help prevent linden bug infestation. The soapy water does not harm plants under any circumstances - on the contrary, because you can also fight other pests, such as aphids.
collect
When collecting, the "favour of the hour" of hibernation should be used. Linden bugs are then almost immobile and can easily be collected or swept out of the cracks in the bark. This is the easiest way to do it:
Lime bugs, Source: gailhampshire from Cradley, Malvern, U.K, Oxycarenus lavaterae - Flickr - gailhampshire (1), Edited by Plantopedia, CC BY 2.0
- Lay out foil or similar around the tree/plant in the size of the plant circumference (to catch the pests)
- Sweep all affected areas with a stiff broom
- If necessary, use a small hand brush to loosen/sweep out pests in the cracks in the bark
- Sweep up fallen bugs and dispose of them in newspaper or other disposable material
- Make sure that the "disposal packaging" is sealed so that "awakened" specimens do not escape
- Alternative to waste disposal: Expose linden bugs far away from the garden
Tip: Because mallow bugs are harmless to plants and humans, the use of chemical pesticides is in no way justified and should therefore not be used to protect the environment and your own health. The above home remedies offer an equally effective solution.
Transplant against new infestation
If you want to be on the safe side that no new infestation will require additional work next year, you can then transplant the affected plant/tree to another location after one of the actions mentioned above, if possible. This prevents any mallow bugs that may still be present in the ground from multiplying and climbing up again. However, since the parasites collect seeds, there is a chance that a new mallow will develop on the spot. If this is removed immediately upon sighting, the linden bugs will look for a new habitat and withdraw.