Mint is a perennial plant. Normally it is quite easy to cultivate. The plants can be grown outdoors, but also in pots on the balcony or terrace. However, despite the fact that the mint is hardy and robust, it can sometimes be affected by pests and diseases. Very often, the velvety green leaves of the mint are then covered with brown spots and dots. As a rule, two diseases are responsible for this.
Mint: brown spots
Brown spots and dots can affect leaves and petioles of mint throughout the growing season. It is important to recognize them in time to treat the plants as soon as possible. The longer nothing is done, the more likely it is that the plants will die sooner or later. They can also infect other plants. Causes of this disease can be
Mint rust & leaf spot disease
This disease is caused by rust fungi, an order of stand fungi. The spores of these fungi, more specifically Puccinia menthae, can infect plants throughout the growing season. Especially a warm and humid climate drastically increases the risk of infection.
Note: The spores of the fungi live as parasites. They do not kill the plant tissue in the process.
During the summer months, it is therefore advisable to regularly inspect the mint plants for changes. This is the only way to act quickly if infection with mint rust has occurred. If small brown spots already appear around the infection site, then mint rust can quickly spread throughout the entire plant. The first symptoms can appear as early as April. These include
- initially chlorotic (light green to yellow) spots and dots on the top of the leaves
- are bordered by leaf veins
- in summer, orange-red to cinnamon-brown fruiting bodies with spores on the underside of the leaf
- after bursting on the upper side of the leaf reddish-yellow bumps around the site of infection
- in autumn additional dark brown to black pustules on the leaf underside
- heavily infected leaves dry up and fall off
- whole shoots wither
- leaf stalks and stems can also be infected
- infestation of the plants occurs from bottom to top
- older leaves are infected first
Note: Infected plants lose their typical mint aroma. These contain up to 60 percent less essential oils compared to healthy plants.
Similar symptoms occur with leaf spot disease. This is very difficult to distinguish from mint rust. Damage is caused by both to the same extent, so their control does not differ either.
Once this and also the leaf spot disease has broken out, no chemical means or also home remedies help in combating it. Further spread can only be contained by radical pruning. it is done as follows:
- cut back all shoots close to the ground
- leave only one dormant eye
- Mint sprouts healthy again there
- Cut back into the household garbage or burn it
- not on the compost heap, danger of spreading
- additionally water the bed with horsetail broth
- repeat the procedure
- this broth strengthens new shoots and protects against rust fungus formation
Note: Mint rust not only affects plants from the labiates family, but also plants from other plant families such as chamomile marigold and monards.
Regular administrations of this broth can increase the resistance of plants to fungal diseases. The high content of silicic acid, as well as potassium and saponins, strengthens the tissues of plants. The leaf surface becomes more resistant and fungal diseases can then not spread so easily.
Field horsetail, also known as “horsetail,” grows wild in moist places such as banks, ditches and meadow edges. Alternatively, other species such as marsh horsetail, pond horsetail, or meadow horsetail can be used.
The preparation of a brew from field horsetail is relatively simple:
- Chop 1 to 1.5 kg of fresh field horsetail with sharp garden shears.
- alternatively, 150 to 200 g of dried horsetail can be used
- soak cuttings in 10 l of water in a large pot
- soak for at least 24 hours
- preferably use rainwater
- then bring everything to the boil briefly
- simmer for 30 minutes at low temperature
- strain the broth with a close-meshed sieve
- allow to cool
- spreading with watering can or pressure sprayer possible
- if using a sprayer, filter brew again through cotton diaper or light cotton cloth
- because plant residues can clog the nozzle
- Dilute broth in a ratio of 1:5 with water
After the first application of field horsetail broth, the process should be repeated every two to three weeks. For this purpose, not only the plants should be treated, but also the soil around them. This will promote resistance and at the same time provide the plants with valuable nutrients.
Tip: The application of the broth should always take place in the morning in sunny weather. Because the warming rays of the sun will enhance the effect of the broth.
Prevent brown mint
Now, before you have to fight brown spots and dots on the leaves of mint, some measures should be taken in advance to prevent these diseases. This does not even require that much effort.
- Use healthy or resistant varieties or species with hairy leaves.
- Multimentha” is recommended for this purpose
- constantly loosen the soil around the plants
- weed regularly
- water plants from below
- damp leaves increase the risk of infection
- always water in the morning
- water regularly, especially during prolonged dry periods and in summer
- avoid waterlogging
- when planting in tubs, provide drainage
- wide planting distance
- to other plants at least 30 cm
- observe crop rotation, annual crop rotation in the bed is advisable
- likes a light sunny to half shady place in the open or on balcony and terrace
- shady places and too short distance to other plants promote the formation of rust fungi
- look for an airy place
- avoid blazing sun and heat, especially at midday
- balanced fertilization in summer months
- use organic fertilizers such as nettle manure or horn shavings
- cut back regularly in autumn
- if necessary, transplant or repot
- timely harvesting prevents the formation of rust fungi
Tip: If brown to black spots appear together with aphids and ants, then sooty mold fungi can quickly form. Aphids and also ants transmit this disease. It is then necessary to act quickly. Immediate radical pruning must be done.
Despite all the preventive measures, it is necessary to regularly check the mint for brown spots and dots. already at the first signs, it is necessary to prune the diseased plants.