Phomopsis blight on eggplant — symptoms and treatment

Severity: medium

What is Phomopsis blight

Phomopsis blight is caused by Phomopsis vexans. It causes fruit rot and stem cankers. Unlike the leaf spot diseases that merely thin the canopy, this fungus goes after the parts of the plant that matter most — it girdles stems and rots the fruit directly, which is why a crop can look reasonable in the field and still be lost at harvest. It is seed-borne as well as debris-borne, meaning it can arrive on the seed you plant rather than from the soil, and that shapes how it is prevented.

Symptoms

The disease shows on leaves, stems and fruit, and it is worth checking all three. On the leaves, brown circular spots appear and enlarge. On the stems, cankers form — sunken, discoloured lesions, typically near the base, that girdle the stem and can kill everything above them; a seedling struck at the base simply collapses. The fruit symptom is the most damaging: a pale soft rot that begins as a sunken spot and spreads until the fruit turns mushy, and it can develop on fruit that looked sound when it was picked. On the older lesions, look closely for small black pycnidia — pinhead-sized black specks studding the dead tissue. These are the fungus's fruiting bodies and they are the diagnostic sign, distinguishing Phomopsis blight from other spots and rots.

• Leaves: brown circular spots
• Stems: cankers, often at the base, girdling the stem
• Fruit: pale soft rot, spreading and sunken
• Diagnostic: small black pycnidia dotting the surface of older lesions

Causes and conditions

The fungus survives on infected seed and on crop debris left in the ground. Seed-borne infection is the route that catches growers out — the disease arrives with the planting material and appears in a clean, well-rotated bed with no obvious source. From debris, spores are splashed by rain and overhead irrigation onto the lower stems and fruit. Warm, wet weather favours it, and fruit resting on wet soil or touching splashed debris is at particular risk.

Treatment

Hot water seed treatment — cultural

Treat seeds in hot water (50°C for 25 min). Use disease-free seed. Rotate crops. This addresses the seed-borne route directly and is the highest-value step available, because it removes the infection before the crop exists. Precision matters: too hot or too long damages germination.

Mancozeb — chemical

Apply contact fungicide preventively from transplanting. Repeat every 7-10 days. Pre-harvest interval: 14 days. As a contact fungicide it must be in place before infection, and reapplied to cover new growth and newly exposed fruit. Pesticide registrations vary by country — check local approval before use.

Prevention

• Start with certified disease-free seed, or hot-water treat your own
• Rotate eggplant out of ground that has carried the disease, and away from other solanaceous crops
• Clear and destroy crop debris at the end of the season — do not turn infected residue back in
• Water at the base and avoid overhead irrigation, which splashes spores onto stems and fruit
• Mulch and stake plants so fruit is kept off wet soil
• Remove and destroy rotting fruit and cankered stems as soon as you find them

Frequently asked questions

Can I eat fruit with a soft rot spot? No — discard rotted fruit. Do not leave it in the plot either, as it feeds the next round of infection.

Is it contagious to other plants? Yes. Splashing water carries spores to nearby eggplants, and infected debris and seed carry it into the following season.

Can I save my own seed from an infected crop? Not without risk. The fungus is seed-borne, so seed from an infected crop can carry it forward. Use disease-free seed or hot-water treat it.