Cucurbit Anthracnose is caused by the fungus Colletotrichum spp and is the most destructive disease of cucurbits or vine crops in warm seasons with frequent rains. The disease occurs worldwide.
The most noticeable symptoms appear on the fruit. Young fruits turn black, shrivel, and die if fruit pedicels are infected. Circular, water-soaked spots develop on the older fruit. These lesions soon become sharply sunken and then pinkish in moist weather, gradually turning dark green to black with flesh-colored, oozing centers.
Most damage from anthracnose generally occurs late in the season after the fruits are well formed.
Cucurbit Anthracnose Cycle
The Colletotrichum fungus overwinters in refuse from a previous vine crop, possibly up to 5 years or in weeds of the cucurbit family. It may be seed borne and is also transmitted by cucumber beetles.
The spores depend upon water for spread and infection. Spread by wash water on harvested fruit is important when cucumbers or melons are cleaned before packing.
Spores may also be spread by cultivating equipment or workers when the foliage is wet. The spotted or striped cucumber beetle can carry the spores from plant to plant within a field or to adjoining fields.
The fungus can penetrate the plant tissue directly and does not require natural openings e.g., stomata or wounds.
Initial infection requires a period of up to 100% relative humidity for 24 hours and a temperature of 20 – 25 °C).
Symptoms may appear within 6 days after infection has taken place.
The fungus may live two years in the absence of a suitable host.
Warm, humid, and rainy weather at frequent intervals is necessary for disease development.
The symptoms of anthracnose vary on different hosts and all aboveground plant parts may become infected.
Small, growing leaves can be distorted and severe spotting may cause entire leaves to blight. The lesions on leaves can initially appear circular, but later coalesce into more irregular necrotic areas. Severe infections can lead to defoliation. Leaf petiole and stem lesions are shallow, elongate and tan.
Infected fruit develops brown to black, sunken, water-soaked spots. Tiny, black fruiting structures, called acervuli, form within the lesions. In wet weather, pink or orange spores ooze from these fruiting bodies. Severely infected fruit are unsightly, insipid or bitter to the taste, and rot quickly when secondary soft-rot organisms invade the broken rind.
When the anthracnose fungus is seed borne the cotyledons droop and wilt, and lesions may form on the stem near the soil line.
Cucurbit Anthracnose Management
The following fungicides are fit for use in prevention and eradication of anthracnose disease in cucurbits.
- RANSOM 600WP 15g/20l
- DUCASSE 250 EW 20ml/20l
- ABSOLUTE 325 SC 10g/20l
- DOMAIN 250 EC 10ml/20l
- BRADLEY 500SC 10ml/20l
- EXPLORER 3SL 10ml/20l
- GREENCOP 500WP 50g/20l
- MEGAPRODE LOCK 525WP 30g/20l
- JUPITER 125SC 15ml/20l
- MILLIONAIRE 690WDG 40g/20l
- RIMETA GOLD 300SC 40ml/20l
- PROVIDENCE 400WP 50g/20l
Non-chemical control method
- Remove and destroy any infected plants or plant parts. Do not compost them.
- Use resistant varieties.
- Plant certified, disease free/healthy planting materials.
- Plant trees in well-drained soil.
- Avoid overhead irrigation to prevent wetting the foliage. Don’t touch the plants when they are wet.
- Ensure rotations with non-host plants, every 2 to 3 years.
- Control all weeds, especially wild and volunteer cucurbits
- To prevent post-harvest losses avoid wounding, i.e. through bruising, scratching, or puncturing the fruits.
- Seed treatment with BIODISTINCTION XTRA helps to control seed coat infections.
- Fungicides should be mixed with INTEGRA 3ml/20l when spraying, which improves the efficacy of the fungicide by acting as a sticker, spreader, wetter and penetrant.
- Alternating different fungicides throughout a plant’s season prevents the fungus from developing resistance over any of the fungicides.
- Timely control of the diseases is very critical as it prevents/reduces losses attributed to anthracnose infection.
- Fungicides should be reapplied after 1 – 2 weeks.
- A proper nutrition boosts plant’s immunity.