Herb leaves have white spots: what to do?

Different causes

If herb leaves develop white spots, action must be taken as quickly as possible so that the herb plants do not suffer major damage and may even die in the end. Before the treatment can be started, the cause of the spots must be clarified. Various causes can be responsible for the white discoloration of the leaves, such as:

• Powdery and downy mildew
• leafhoppers
• spider mites and
• care mistakes

Care mistakes should not be underestimated when growing herbs. They can lead to a wide variety of diseases. Below are some observations on the individual causes, how to combat them and preventive measures.

Powdery mildew (Erysiphaceae)

Powdery mildew, whether true or false, is caused by various sac fungi. Powdery mildew is also known as the “fair weather fungus” because it occurs in dry, warm weather. It can be found more often after hot days and cool nights with increased dew formation. All green parts of the plant can be affected and even die under certain circumstances. The powdery mildew overwinters on the living plant, on the shoots or in the leaf buds. Powdery mildew can be recognized by the following symptoms

• occurring from March to August
• whitish-grey coating on the upper side of the leaves
• white spots are mealy
• later turning brownish
• Coating can be wiped away
• Infestation of the entire leaf possible
• thereby removing water and nutrients
• leaf dried up
• stems and flowers are also affected

Downy mildew (Peronospora)

In contrast to powdery mildew, downy mildew is referred to as the “bad weather fungus”. It needs moisture to grow. It occurs preferably in prolonged wet weather, for example more often in rainy summers, but also in spring and autumn. are symptoms of an infestation

• white spots or coating on the underside of the leaves
• sometimes also slightly greyish in colour, later brown
• The upper side of the leaf has yellow-brownish spots
• also affects stems and flowers

combat powdery mildew

As soon as signs of powdery mildew infestation of the herbs become visible, this must be combated immediately so that it does not spread to other plants and ultimately even die. First measures are

• cut off all affected leaves
• Disposal in residual waste
• not on the compost
• otherwise fungal spores will be spread by wind

There are also various home remedies that can be used to combat it. These should be preferred to chemical pesticides. There are effective home remedies

milk

• only use fresh milk
• Make a mixture of one part milk and eight parts water
• Spray affected plants every few days

garlic broth

• crush two cloves of garlic
• Boil 0.5 liters of water
• pour over garlic
• Leave for 1 hour, strain
• spray plants with it

baking powder

• 3 packets of baking powder
• 50 ml oil such as rapeseed oil
• 5 liters of water, lukewarm
• 2 to 3 drops of dish soap
• mix everything well
• spray plants every 10 to 14 days
• Repeat the application five to eight times

Alternative: Soda

• 1 parcel
• 20ml oil
• 2 liters of water

Rainfarnbrühe

• Chop 5 to 6 fern fronds
• pour over 2 liters of boiled water
• Leave for 2 hours, strain
• sprinkle herbs daily
• directly on herb leaves

Alternative: horsetail or nettle manure

• 30 g dried or 300 g fresh leaves
• Add 10 liters of water
• leave everything for 24 hours
• then boil for 15 minutes, strain
• let cool down
• Dilute with water in a ratio of 1: 5 when using

Use of ladybugs

• 16-spotted ladybird (Halyzia sedecimguttata)
• 5 to 7 mm in size
• colored orange-brown
• typical are white spots
• 22-Punktkäfer (Psyllobora twenty-twopunctata)
• 3 to 4.5 mm in size
• yellow with black dots

Neem oil from the fruits of the Indian neem tree can also be used. The oil has an antifungal effect. If nothing helps, a radical pruning should be done. In very stubborn cases, chemical agents have to be used, these usually contain copper or sulfur to combat mildew. Compo Bio mildew-free Thiovit is recommended . The remedy should be used at intervals of eight to twelve days.

preventive measures

However, it does not always have to be an infestation with powdery mildew if various preventive measures are observed.

• larger planting distances
• Leaves dry well after rain
• Avoid waterlogging
• Planting on well drained soil
• do not moisten herb leaves when watering
• pour from below
• preferably watering in the morning or in the evening
• regular weed removal
• Avoid nitrogen over-fertilization
• plant resistant varieties
• Shorten the shoot tips by 5 cm at the end of August
• powdery mildew fungi like to overwinter there
• Strengthen herbs with doses of horsetail broth
• Plant garlic, chives, basil and chervil alternately between individual herbs

Blattzikaden (Typhlocybinae)

These equal-winged creatures are 2.6 to 3.3 mm in size and yellow-green in colour. The head is decorated with three black spots. They often appear in warm summers. The following signs indicate the presence of these pests:

• white to silvery spots on the leaves
• later brown discoloration
• Leaves usually die off
• if the infestation is severe, the entire plant dies off

fight cicadas

Fighting these tiny creatures isn’t exactly easy. The following measures are helpful

• Spraying the leaves with vinegar essence, heavily diluted
• best in the early morning hours
• must be calm
• Setting up yellow stickers, yellow boards
• Control of the larvae with universal insecticides such as Neem Azal T/S
• Spray a mixture of 1l water, 1.5 ml Rimulgan, 5 ml neem oil

preventive measures

• Setting up yellow boards
• Cover plants with insect protection netting
• powder herbs with rock dust in spring and autumn
• When planting new plants, ensure appropriate spacing
• Attract birds to the garden
• are natural enemies

Spinnmilben (Tetranychide)

They cannot be seen with the naked eye because the arachnids are only up to 0.8 mm in size. They mainly appear in dry weather and suck the sap from the underside of the leaves. A favorite target of spider mites is oregano . signs are

• small white spots or spots on leaf surface
• Sucking sites usually lighter colored
• white webs cover the plants
• over time the leaves dry up

Fight spider mites

It’s good to know that spider mites don’t like moisture. When an infestation is detected, quick action is required:

• remove affected plant parts
• Disposal in residual waste
• increase in humidity
• mulch plants outdoors
• water thoroughly on warm days
• shower affected plants with a moderate jet of water
• possibly wrap plants with foil afterwards
• Use a mixture of 0.5 l water and 15 ml liquid soft soap
• sprinkle leaves with it
• Leave on for 15 minutes
• Fertilization with cigarette ash

preventive measures

• Use of nettle and field horsetail to strengthen plants
• pouring with cold extract from garlic and onion skins is also possible
• spray with a decoction of seeds (pressed) from the neem tree
• Predatory mites of the Phytoseiulus persimilis variety help
• Use of ladybirds, parasitic wasps
• Creation of dead wood corners
• Setting up insect hotels

care mistakes

There are also various care mistakes that must be observed so that there are no white spots on the leaves of the herbs. Effective care measures are:

• look for a sunny location
• for permeable soils
• not cause waterlogging
• Loosen the soil regularly
• remove weeds
• cut back regularly
• fertilize and water regularly