What are these brown spots on my conker tree’s leaves?

Horse Chestnut Leaf Blotch is a fungal condition called Guignardia aesculi that affects horse chestnuts, not sweet chestnut.

The main symptom is irregular brown blotches on the leaves, starting at the edges, from late June.

• Unlike leaf miner damage, these blotches are chestnut brown and tend to be irregular and rounded.
• Leaf miners tend to burrow between two veins, making bands of damage that are lighter in colour.
• By the middle of September, the two conditions look very similar, and the end result of early de-foliation is the same.

Although Horse Chestnut leaf blotch is not pretty, it does not significantly affect the strength or health of the infected tree, unlike Bleeding Canker.

Horse Chestnut Leaf Blotch Treatment

The fungal spores overwinter in fallen leaves, rising again into the trees in spring.

Therefore, the only realistic control-prevention is to break the cycle by raking up and burning or binning the fallen leaves.

There are no fungicides on the market for Horse Chestnut Leaf Blotch, and in any case spraying a mature tree is not realistic.