Leaf spot on eggplant — symptoms and treatment

Severity: medium

What is Leaf spot

Leaf spot diseases in eggplant are caused by various fungi including Cercospora and Alternaria. They cause circular spots on foliage. Rather than one disease, this is a group of fungal pathogens that produce a similar picture on the leaves and respond to the same management. They rarely kill an eggplant outright, but they defoliate it from the bottom up, and a plant steadily losing its lower leaves has less capacity to fill fruit — plus the fruit it does set is left exposed to the sun.

Symptoms

The spots are circular and brown or tan, and they usually start on the oldest, lowest leaves — the ones closest to the soil, where spores splash up and moisture lingers longest. Spots may have concentric rings, giving them a target-like or bullseye appearance as the lesion expands in pulses; this ringed pattern is characteristic of Alternaria. Yellowing appears around the lesions and spreads until it takes in the whole leaf, and premature leaf drop follows — the plant sheds affected leaves and the bare zone works its way up the stem. Where spots are numerous they run together into large dead patches before the leaf falls.

• Early: small circular brown or tan spots on the lower, older leaves
• Progressing: spots enlarge, some showing concentric rings; yellowing around the lesions
• Advanced: spots merge, leaves yellow fully and drop prematurely; defoliation moves up the plant

Distinguishing which fungus is responsible matters less than you might expect — the cultural and chemical management is the same either way.

Causes and conditions

These fungi survive between seasons on crop debris and in the soil, which is why the first spots appear on the leaves nearest the ground. Rain and overhead irrigation splash spores from that debris onto the lowest foliage, and from there upward through the canopy, drop by drop. Infection requires leaf wetness, so the disease advances during wet weather, in prolonged dew, and in dense plantings where leaves stay damp for hours. Continuous cropping of solanaceous plants in the same ground builds up the inoculum year after year.

Treatment

Crop rotation and sanitation — cultural

Rotate with non-solanaceous crops for 2-3 years. Remove crop debris. Avoid overhead irrigation. This is the foundation of control, since it attacks the source: rotation starves the soil-borne inoculum, debris removal takes away where it overwinters, and base watering denies it the splash it needs to travel.

Chlorothalonil — chemical

Apply contact fungicide preventively every 7-10 days during wet weather. Pre-harvest interval: 14 days. As a contact product it protects only the tissue it covers, so it must go on before infection and be reapplied to protect new growth — spraying visible spots will not clear them. Pesticide registrations vary by country — check local approval before use.

Prevention

• Rotate eggplant with non-solanaceous crops, keeping it away from tomatoes, peppers and potatoes in the sequence
• Clear and destroy crop debris at the end of the season rather than turning it in
• Water at the base of the plant and never overhead, especially late in the day
• Space plants so air moves through and leaves dry quickly after rain or dew
• Mulch the soil surface to stop rain splashing spores up onto the lowest leaves
• Remove the lowest affected leaves early, before the spots multiply upward

Frequently asked questions

Is it contagious to other plants? Yes — to nearby eggplants, and the related fungi affect other solanaceous crops, which is why the rotation excludes tomatoes, peppers and potatoes.

Can I eat the fruit? Yes. These fungi attack the foliage. Observe the pre-harvest interval for any fungicide you have applied.

When should I treat? Preventively, during wet weather, before spots appear or at the very first ones. A contact fungicide is a shield, not a cure.