If the lavender gets yellow leaves with more or less large brown to black spots, the plant is infected with the dreaded leaf spot disease. This is sometimes called shotgun disease because the leaves can look like they have holes in them.
Causes of leaf spot disease
Various fungi of the genera Septoria, Ascochyta or Alternaria cause this disease, which is noticeable by a yellowish discoloration of the leaves and reddish, brown or black spots. Like all fungal diseases, leaf spot spreads rapidly and eventually leads to the death of the plant. Such fungi mainly attack weakened plants that are too moist, too crowded or in an unsuitable location. Especially in cold and humid summers fungal attack on lavender occurs frequently.
Prevent fungal infection
Since it is difficult to control a fungal disease, prevention is an important measure. Therefore, with lavender you should
- too much moisture, especially waterlogging
- too close planting
- a planting on unsuitable (loamy or peaty) soils,
- intensive fertilization, especially with – nitrogen
- incorrect overwintering
- as well as insufficient light (half-shady or shady location).
- avoid. Incidentally, the fungi survive even severe winters, as they simply overwinter on the plant or leave spores. These can then continue to operate in the following year and cause the lavender to die.
Combat usually only possible by cutting away large areas.
As soon as leaves, sometimes also stems, of the lavender are infested, you should tackle the fungus with hedge shears (105,00€ at Amazon*). Cut the lavender back vigorously to the healthy and not yet infested parts. However, you should avoid cutting back to the wood, because then the plant usually no longer sprouts. Afterwards, carefully disinfect the tools so that any remaining spores are killed. Unless you want to harvest the plant, you can also use a broad-spectrum fungicide.
Tips & Tricks
If, on the other hand, the lavender turns brown and looks as if it has dried out, then the cause is usually root rot caused by waterlogging or else incorrect watering.