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Mentha is one of the perennial herbs that no garden should be without. The plants are generally very robust and rarely become ill. In optimal conditions, they spread rapidly in the garden. If the mint suddenly turns yellow, something is wrong and you need to act. It is often heat and drought that cause problems for the plant, but various diseases and pests can also be the cause.
pests
There are countless animal pests in the garden, but they generally avoid the different Mentha species. Their essential oils protect the plant from the insects to a certain extent. Most pests feed on the plant saps, some also eat the leaves. If left untreated, a severe infestation can kill the mint.
aphids
Aphids prefer to stay on fresh shoot tips and on the underside of the leaves. They are very small and have a globular, mostly greenish body. Aphids excrete a sugary, sticky substance called honeydew. This promotes the growth of sooty mold fungi on the plants, which can be recognized by its black color.
damage picture
- yellow leaves
- stunted shoots
- necrotic spots
- black shoot tips
First aid
If the aphid population is limited to just a few leaves or shoots, cut them out. Robust plants can be washed off with a sharp jet of water. A soap or neem oil solution has proven effective in combating it. If the infestation is severe, it is easier to cut the entire plant down to the ground.
Flea Beetle (Psylliodes)
Ground flea larva. Source: Gilles San Martin from Namur, Belgium, Psylliodes chrysocephala larva (31943653745), crop from Plantopedia, CC BY-SA 2.0
Ground flea beetles, also known as ground fleas, are only around two millimeters long. Your body is yellow-brown to reddish, the elytra mostly yellow. The adult beetles hibernate in the ground and start laying their eggs in spring after they have attacked the mint leaves. However, the cause of the death of the peppermint is usually hidden in the ground, because the tiny larvae eat at the roots from April.
symptoms
- tiny, round holes in the leaves
- yellow leaves and death of the mint due to root damage
measures
Flea beetles can be combated naturally with plant manure made from wormwood or tansy. A solution of cooked onions or garlic also repels the little animals. In addition, it makes sense to put a board coated with caterpillar glue next to the mint. Jumping flea beetles stick to the glue.
Tip: Frequent hoeing and keeping the soil moist minimizes the risk of infestation.
Mint Leaf Beetle (Chrysolina spp.)
Chrysolina coerulans
Occasionally, the mint leaf beetle appears on the mint from April or May. The beetles are easily recognizable by their shiny metallic exterior. Depending on the species, the beetles can be green, blue or even copper-colored to black.
damage picture
- leaf edge damage (mainly on the shoot tips)
- brown, shiny larvae on the underside of the leaves from June
combat
Cut back affected shoots early to reduce the number of eggs. It also makes sense to spray on a solution of soap with a little rapeseed oil to contain the population. If in doubt, cut the plant back to the first leaf.
Leafhoppers (Eupteryx spec.)
Eupteryx notata. Source: AfroBrazilian, Eupteryx notata 03, crop from Plantopedia, CC BY-SA 4.0
The flying insects mainly attack mints such as basil, marjoram, oregano, sage, thyme and also mint. The cicadas are only two to four millimeters in size and have yellowish to grey-green spots. Shake the plant and the insects will jump up and fly away.
symptoms
- punctiform brightening on the leaves
- yellowing of the leaves
combat
It is not necessary to combat the cicadas. As a rule, the damage is not particularly great and the Mentha is still suitable for consumption. If the little animals bother you, you can attract them with yellow boards and catch them.
Diseases
Pathogens such as bacteria, viruses or fungi can penetrate the plant via the roots or wounds and cause great damage there. The most common diseases in mint include:
mint rust
Jerzy Opioła, Puccinia menthae a1 (7), crop from Plantopedia, CC BY-SA 4.0
Among the many species of rust fungi that attack plants in our gardens, there is one that specializes in mints. The cause of the disease is a fungus called Puccinia menthae, which thrives in damp weather. It spreads very quickly and quickly affects plants in neighboring beds and gardens. This includes not only Mentha species, but many other herbs such as marjoram, savory and oregano.
symptoms
- light yellow or rusty brown spots on stems and leaves
- pale and stunted young shoots
- withering of the whole plant
First aid
An early pruning at the first symptoms often creates a remedy. Heavily infected mints can usually no longer be saved. To prevent the fungus from spreading further, remove as many diseased plants and their roots from the bed as possible.
preventive measures
The risk of disease can be minimized by removing all dead shoots and leaves in autumn and disposing of them in the household waste. Sufficient distance between individual plants allows air to circulate better and moisture to dry out.
Tip: Preferably plant resistant varieties such as 'Multimentha'.
mildew
Powdery mildew on maple leaf. Source: Jerzy Opioła, Powdery Mildew Acer DK43 (1), crop from Plantopedia, CC BY-SA 4.0
Powdery mildew spores are found almost everywhere. While powdery mildew tends to occur in warm and dry conditions, downy mildew is an absolute bad weather fungus. He loves the humidity. Although they are different types of fungi, the symptoms and treatment are very similar.
damage picture
- white, powdery spots on leaves and stems
- later: yellowing and browning of the leaves
- death of the plant
combat
Remove all affected leaves and shoots as soon as the first symptoms appear. The fungus can be easily combated with plant broths. These include field horsetail, tansy or garlic broth. If in doubt, it makes sense to cut off the entire shoots close to the ground.
Notice: The cuttings of diseased plants must be disposed of with household waste.
environmental factors
If the mint is exposed to dry winds, frost or even extreme heat, it gets yellow leaves. Potted plants are particularly sensitive to these factors. If these are in the blazing sun, not only the foliage but also the roots can be damaged by the heat and lack of water. The most common causes of yellow leaves include:
- dryness
- waterlogging (root rot)
- Temperature shock from water that is too cold
- Potted plants: too sunny location (especially in the root area)