Alternaria blight is a fungal disease caused by pathogenic members of the Alternaria genus. It leads to the development of leaf spots that turn from small brown spots (often with yellow halo) into irregular brown spots. Eventually, the leaves can turn brown, curl and die.
Leaf spots start as small brown spots, often with a yellow halo, and grow into irregular brown spots (up to 3/4"). Leaf spots sometimes develop a target-like pattern of rings. Severely infected leaves turn brown, curl upward, wither and die.
Avoid overhead watering to limit leaf wetness, and allow enough space at planting time for good air circulation and ample sun penetration. Keep your garden free of fallen leaves all season, and especially thorough at fall cleanup time.
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