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There is a wide variety of herbs. They are very popular as a spice, decoration of dishes and in the relief of diseases. No wonder there is a trend towards growing herbs in your own garden. A cookie is available everywhere. After all, sage, thyme, peppermint and co need little space and are quite frugal in their care. They even thrive in pots on the balcony. Sometimes, however, it can happen that white spots appear on the herbs. It is then important to act as quickly as possible to prevent it from spreading.
Causes of white spots on the leaves
If the leaflets of herbs turn white, then the cause must be investigated as quickly as possible in order to take appropriate measures to prevent spread. In the worst case, the plants can die. Reasons for this can be:
- mildew
- spider mites
- leafhoppers
- care mistakes
powdery mildew
Powdery mildew is caused by a fungus and is also known as the "fair weather fungus" because the fungal spores multiply and spread particularly quickly in warm, dry weather and when dew forms at night. The mushrooms love temperatures around
20 °C and a humidity of 70 percent. The mildew fungus belongs to the sac fungi. It penetrates the outer cell layer of leaves, stems and flowers. Nutrients and water are withdrawn from the host plant. Mainly peppermint, parsley, lemon balm, oregano, rosemary, borage and sage are attacked with powdery mildew.
Powdery mildew on a willow
symptoms
- Dry plants most commonly affected
- Mainly occurring in the months of May to August
- Velvety white-grey coating on the upper side of the leaf
- Initially only small white, floury spots visible on the leaf
- Increasingly, the entire leaf is affected
- Coating can be wiped away with fingers
- In an advanced stage, the discoloration of the covering is dirty brown
- Leaves eventually dry up
- If the infestation is severe, the plant dies
The powdery mildew must not be mixed with the downy mildew be confused. This is also known as the "bad weather fungus" because it loves moisture. He is recognizable
- on both sides of the leaf
- white coating on underside of leaf
- brightening or yellow spots visible on the upper side of the leaf
Downy mildew on cucumber plant
countermeasures
When the first signs of stains appear, action is required. Prompt treatment of affected plants can prevent the disease from spreading. Above all is important
- Remove infested leaves
- Dispose of with household waste or burn, not on the compost
Before resorting to chemical mace, biological measures should be used first. Here are some home remedies that are helpful in fighting powdery mildew.
- Treatment with milk, mix fresh milk with water in a ratio of 1:8, spray the plant every few days
- Spritz with garlic tea, pour ½ liter of boiling water over 2 thick cloves and allow to cool
- Spray with broth made from 3 packets of baking powder, 50 ml rapeseed oil, 5 l lukewarm water, a few drops of dishwashing liquid every 10 to 14 days, 5 to 8 applications are sufficient
- Use of nettle, tansy or field horsetail broth
- Use of ladybirds and sawflies
- In very acute cases, radical pruning is necessary
If nothing helps, chemical agents can be used to combat mildew. Among other things, Compo Bio mildew-free Thiovit Jet can be used. Treatments are spaced 8 to 12 days apart.
nettle broth
tip: Field horsetail broth is siliceous and strengthens the leaf surface. To prepare it, soak 300 g of fresh or 30 g of dried field horsetail in 10 l of water for 24 hours. Then heated and boiled for 15 minutes. When cooled, it is diluted with water in a ratio of 1:5.
prophylactic measures
- Choose sufficiently large planting distances so that leaves can dry off after rain
- No waterlogging, but permeable soil necessary
- Water only when soil surface has dried
- Do not wet the leaves, always water from below, in the morning and in the evening
- Removing weeds regularly can be carriers
- Cutting shoot tips in autumn provides good hiding places for powdery mildew
- No over-fertilization, be particularly careful with nitrogen
- Choose resistant varieties
- Plant strengthening with field horsetail broth
- Spray with 20 ml fennel oil, 7.5 ml soy lecithin and 5 l water
tip: Keep planting garlic, chives or chervil between the individual herbs. These help curb powdery mildew.
spider mites
The small suckers can hardly be seen with the naked eye. Because they are only up to 0.8 mm in size. Spider mites are located on the underside of the leaves, stinging them and sucking out the plant juices. The spread occurs mainly in dry, warm weather. Oregano is very commonly attacked. Spider mites can be recognized by the following symptoms:
- Small, white speckles on the upper side of the leaf
- threads between the plant parts
- Web can cover whole plants
- If the infestation is severe, the leaves will dry up
Spider mite infestation
Fight spider mites
The small suckers are usually easy to combat if the causes of the infestation are eliminated. Spider mites don't like moisture. Now there are various ways to get rid of the pests:
- Increase humidity by ventilating the greenhouse well
- Provide even moisture outdoors by mulching
- Water thoroughly on hot days
- Rinse infested plants with a strong jet of water, especially the undersides of the leaves
- Spraying with a decoction of nettles, field horsetail or wormwood
- Fertilization with cigarette ash
- Spray with 500 ml water and 15 ml dissolved potash soap, moisten affected leaves with it for 15 minutes
- As a preventive measure, pour onion broth as a cold water extract from onion and garlic skins at intervals
- Prophylactic use of a decoction made from pressed seeds of the Indian nee tree
When using chemical pesticides, the plants can quickly become resistant. Repeated treatment with acaricides is then always necessary.
leafhoppers
The leaf cicadas belong to the equal-winged species. There are 45,000 species worldwide. In warm areas they emit buzzing sounds, but in Germany the little animals are known as pests. The cicada reaches a size of 2.6 to 3.3 mm and is yellow-green in colour. The head has three black spots and two on top of the forehead.
Leafhoppers mainly attack sage, thyme, basil, lemon balm, marjoram, but also other herbs, especially perennial crops.
Leafhopper, Typhlocybinae
symptoms
- White to silvery mottling over the entire leaf, possible transfer of fungal spores
- Later browning of the leaves and eventual death
- Cicadas visible in sunshine and warm weather
- In severe infestation, the plant dies
Direct Combat
Controlling leaf cicadas is quite difficult. The following measures can be helpful:
- In the early hours of the morning when there is no wind, spray the underside of the leaves with heavily diluted vinegar essence
- Installation of yellow boards or yellow stickers
- Spray with a solution of 5 ml neem oil, 1.5 ml Rimulgan and 1 l water
- Use universal insecticides such as Neem Azal T/S to treat the larvae
preventive measures
It does not always have to be an infestation with cicadas, preventive action is then necessary. Herbs can be protected from the equal-winged insects with simple means:
- Setting up yellow boards
- Covering the plants with insect protection nets
- Powder the herbs with rock flour in spring and late autumn
- When planting new plants, keep away from infested plants
care mistakes
Sometimes incorrect care of herbs can result in a white discoloration of the leaves. It is therefore important to give the plants proper care from the outset. It starts with the choice of location. Furthermore, the following must be observed:
- Sunny location, but no direct sunlight, otherwise leaves can get sunburned
- Soil must be permeable, no waterlogging
- Loosen the soil between plants so that air can reach the roots and water and nutrients can be better absorbed
- Watering directly into the root area, morning and evening
- Water only when the surface of the soil has dried
- Do not wet leaves
- Remove weeds regularly
- Regularly break out the tips of the shoots and possibly the beginnings of the flowers
- Use small amounts of horn meal, liquid organic complete fertilizer or primary rock meal (minerals and trace elements) for fertilization
- Regular top-up fertilizer for heavy feeders such as basil, lovage, chives and parsley
Mint, Mentha