Thyme is a popular Mediterranean culinary and aromatic herb with numerous species of different qualities. But what can be the reason if the thyme leaves get white spots and what can you do?
Table of Contents
Zikaden
These cicadas are two to four millimeters small, slender, greenish-yellow animals, mostly with a brown-black mottled surface. They sit mainly on the undersides of the leaves, are very easily frightened and have exceptional jumping ability. Dry and mild weather can favor an infestation. The greatest emergence of adult animals can be observed in July. The first symptoms of an infestation can be seen around mid-May.
damage picture
- Thyme leaves show small dot-like white spots
- Leaf green is disappearing more and more
- eventually disappeared completely
- white areas become larger and merge into one another
- often whitish moulting residues on the undersides of the leaves
- Leaf edges partially show necrosis
- Some of the thyme leaves die off
- Plants are weakened but do not die
Fight
- Is difficult
- Yellow boards or yellow stickers can partially intercept pests
- against the larvae neem preparations very effective
- Beneficial insects not endangered by the oil
- If possible, avoid treatment during flowering
- radical pruning after harvest can decimate infestations
- the use of potash soap and pyrethrum is also helpful
prevention
In order to prevent cicadas, crop rotation should be observed and thyme should not be grown where a cicadas infestation has previously occurred. Affected plants should not overwinter in the greenhouse and should be pruned vigorously after harvest. Regular removal of weeds is also recommended.
spider mites
Spider mites are extremely small, measuring less than a millimeter in size, and can hardly be seen with the naked eye. They only live for a few weeks, but lay up to 100 eggs during this time. The next generation hatches just three days after the eggs are laid. They feel particularly comfortable in warm locations with low humidity. Infestation can occur in spring and autumn.
damage picture
- Thyme in the greenhouse particularly affected
- Signs of infestation, fine white webs
- and numerous small white spots
- which are caused by the biting tools of the animals
- and the tapping of the plant sap
- Protection against evaporation of affected thyme leaves is disturbed
- they wither and fall off
- usually the shoot tips are also affected and die off as well
Fight
- remove affected plant parts
- shower every other day with a strong jet of water
- or spray thyme leaves with rapeseed oil
- alternatively, mix tea tree oil with water
- 15 drops of tea tree oil and 500 milliliters of water
- Shake mixture well
- Spray plants several times a day
- neem oil is also effective
- do not use together with predatory mites
- Use of predatory mites only in the greenhouse
- Repeat spraying several times at appropriate intervals
prevention
Since spider mites prefer to attack already weakened plants, it is important to ensure optimal conditions and proper care. This includes, among other things, balanced but economical fertilization in order to strengthen the plant tissue and make the plants more resistant. Sufficient humidity should be ensured in the greenhouse.
mildew
If thyme leaves show white spots, powdery mildew or powdery mildew can be the cause. Both are caused by different fungi. Differences can also be found in their appearance and based on their origin with regard to the weather conditions.
powdery mildew
Powdery mildew is a so-called “fair weather fungus” because it occurs in warm and dry weather. Alternating humidity and drought favor an infestation. In contrast to downy mildew, real mildew does not penetrate into deeper layers of tissue.
- Thyme leaves initially branch out with small white spots
- soon grow larger and run into each other
- flowers can also be affected
- white spots can be wiped off
- mealy coating, later dirty-brownish
- Leaves turn brown and dry up
- the flowers wither and die
- heavy infestation can lead to the death of entire parts of the plant
Wrong mildew
As a so-called “bad weather fungus”, it needs permanently damp, cool weather in order to be able to spread. As a result, it occurs mainly in spring and autumn. Nevertheless, it is rarer than powdery mildew but no less dangerous because it penetrates into the plant tissue.
damage picture
Both sides of the leaf are affected by downy mildew. However, it mainly spreads on the undersides of the leaves. There are white spots or white-spotted spore lawns. It is partly violet in color and cannot be wiped away. Yellowish spots can be seen on the upper side of the leaves. Affected thyme leaves die off, and if left untreated, the entire plant dies as well.
combat powdery mildew
- Remove and discard affected plant parts
- Help promises spray solution made of milk and water
- mix in a ratio of 1:9
- Lactic acid bacteria act against the fungus
- Sodium phosphate in milk strengthens the plants
- Spray the thyme thoroughly with it
- Don’t forget the underside of the leaves
- repeat every few days
- natural enemies are ladybird larvae
preventive measures
- avoid too dense planting
- pour as needed
- preferably in the morning and not over the thyme leaves
- Avoid over-fertilization with nitrogen
- Strengthen the thyme with horsetail stock
- prefer resistant varieties if possible
- treat preventively with copper lime
frequently asked Questions
A cover with close-meshed culture protection nets can be helpful in the sense that they prevent the cicadas from flying in and thus prevent egg laying.
Appropriate fungicides against powdery mildew are commercially available. However, it is not advisable to use thyme or any other herb that is intended to be eaten or used in the kitchen. Otherwise there is a risk of ingesting residues of these substances when consuming thyme. In addition, soil organisms and indirectly also beneficial insects can be harmed.
Powdery mildew in particular is highly contagious and can spread to vegetables or ornamental plants. Transmission occurs primarily through the wind. The fungus hibernates on dead plant parts on the ground and can attack the plants again in spring.
