Anthracnose

This entry groups two fungal leaf-spot diseases with identical treatment and prevention: anthracnose (round to slightly-angular spots, a paler sunken centre with a dark margin, developing shot-holes when severe) and Cercospora leaf spot (Cercospora rosicola — concentric target lesions with a tan, paler centre). Both are true fungi and are managed the same way. Distinguish them from downy mildew (angular, vein-bounded lesions with grey mould on the underside), which needs different treatment.

Anthracnose is a fungal disease caused by Sphaceloma rosarum or Colletotrichum spp. It typically develops under conditions of high humidity (>80%), warm temperatures (25–26 °C), and prolonged wet weather. Early lesions appear as small grey-brown to yellow-brown spots that are slightly sunken at the centre. As the disease progresses, lesions expand into irregular grey patches surrounded by reddish-brown margins. In severe infections the affected tissue dries out and develops shot-holes, or leaves become partly necrotic, yellow, and prematurely abscise. On stems and shoots, the fungus causes brown lesions that lead to stem shrinkage, distortion, and increased brittleness. On flowers, brown spots appear on the petals, causing them to wilt and drop early.

Mechanism behind the circular spots and shot-holes. These leaf-spot fungi are necrotrophic: on contact with the leaf they secrete powerful degradative enzymes — cellulase and pectinase — that liquefy and kill leaf cells so the fungus can absorb the released nutrients. The toxins diffuse outward radially — like ink spreading on blotting paper — and are potent enough to eat straight through the smaller veins, producing a fully formed circular lesion that the leaf architecture cannot constrain. In Cercospora leaf spot specifically, the stacked dark concentric rings (the target pattern) are a footprint of the diurnal weather cycle: under humid nights the fungus advances aggressively, then halts during dry days and sporulates, laying down successive dark borders. The lesion centre — where the fungus exhausts the cells and draws out moisture first — becomes desiccated necrotic tissue, paper-thin and brittle; wind, rain, or irrigation easily punches it out, leaving the round shot-holes that define the disease.

As soon as lesions are detected, act decisively:

• Hard pruning: Aggressively remove all diseased leaves and shoots. Bag and destroy the debris (burn or dispose of off-site); never leave it at the base of the plant or compost it, as the inoculum remains viable.
• Sanitation: Collect and dispose of fallen leaves around the base of the plant.
• Isolation: For potted roses, move the affected plant to a separate, well-ventilated area. Isolate the plant if it is growing near other susceptible hosts.
• Reduce leaf wetness: Temporarily stop overhead watering — water only at the soil level.
• Fungicide application: Use systemic and contact fungicides to eradicate the fungus from inside the leaf tissue.

Recommended products

The three most widely used and effective products are:

1. Amistar Top 325SC (Syngenta)

A premium fungicide with strong systemic activity that penetrates leaf tissue rapidly.

• Description: Contains Azoxystrobin and Difenoconazole — eradicates the pathogen from within and promotes thicker, greener foliage after recovery.
• Dosage: 10 ml per 16–20 L of water.
• Application: Spray to thoroughly wet both leaf surfaces and the stems.
• Frequency: Two applications, 5–7 days apart.
• Where to buy: Shopee — Amistar Top genuine

2. Antracol 70WP (Bayer)

A widely trusted fungicide that also supplies micronutrient zinc, hardening the foliage.

• Description: Active ingredient Propineb in wettable powder form; creates a protective film that blocks fungal penetration.
• Dosage: 25–30 g per 16 L of water.
• Application: Spray at the first sign of lesions, or as a preventive after extended rainy periods.
• Frequency: Curative — 2 sprays 5 days apart. Preventive — every 10–15 days.
• Where to buy: Lazada — Antracol Bayer

3. Anvil 5SC (Syngenta)

Highly effective against leaf-spot diseases, anthracnose, and rust at a reasonable price point.

• Description: Active ingredient Hexaconazole — translaminar with persistent residual activity.
• Dosage: 20 ml per 16 L of water.
• Application: Spray thoroughly into leaf axils and crevices where the fungus typically shelters.
• Frequency: Repeat after 7 days to eliminate residual inoculum.
• Where to buy: Shopee — Anvil 5SC

• Maintain an open canopy and avoid wetting the foliage when watering.
• Prune regularly to reduce humidity within the canopy.
• Apply preventive copper-based fungicide sprays every 2–4 weeks.
• Avoid prolonged leaf wetness — never let water stand on the foliage.