Prevention of anthracnose on dragon fruit

Anthracnose on dragon fruit is caused by the fungus Colletotrichum, which attacks branches, flower buds and young fruit. Instructions for distinguishing from black rust spots, seasonal prevention and treatment regimen for orchards in Binh Thuan, Long An.

Summary: Anthracnose is one of the two most common diseases on dragon fruit, along with black spot. Many orcharders confuse these two diseases even though the causes and treatments are different. This article focuses on anthracnose — clearly distinguishing it from black spot, providing guidance on seasonal prevention and early treatment of disease outbreaks to protect the productivity of white-flesh and red-flesh dragon fruit orchards.

Applies to: Dragon fruit in Binh Thuan, Long An, Tien Giang, Vinh Long, Tay Ninh. Both white and red intestines are affected.
Duration: Room all year round. The pressure is strongest in May-September, the rainy season.
Difficulty level: Medium.
Estimated additional costs: 3-5 million VND per hectare per year for periodic rooms.

Agents and distinction from black spots

Anthracnose is caused by the fungus *Colletotrichum gloeosporioides*. Other characteristics of black spots (caused by *Neoscytalidium dimidiatum*):

Criteria	Anthracnose	Rust black spots
Spots on branches	Small round 3-10 millimeters, brown border, gray-white center	The spots are larger, rough, deeply concave, dark black
Spotted center	There are tiny black dots (fungal spores) when the weather is humid	No obvious spore spots
On flowers	The petals are dark brown, not blooming	Less harmful to flowers
On young fruit	Small round black spot on the shell, possibly pus	Concave black spots, cracked shell
Strong season	May-September is humid	All year round, especially the rainy season

Correct distinction helps choose effective active ingredients. Two diseases are sometimes present in the same orchard — requiring broad-spectrum spraying or a combination of active ingredients.

Conditions where anthracnose thrives

Anthracnose fungus develops when:

Air humidity above 85 percent lasts 8-12 hours.
Temperature 24-30 degrees Celsius — the rainy season in Binh Thuan and Long An is around this time.
Long-term rain lasting more than 3 consecutive days creates contagious spores.
The canopy is too thick — moisture accumulates in the canopy.
The plant lacks potassium and calcium — soft tissue can easily penetrate.

*Colletotrichum* spores live on dry branches, fruit falls at the base, and can survive 4-8 months. This year there is an outbreak in the orchard without cleaning at the end of the season, then next year it will flare up again right from the first rain of the season.

Symptoms on three plant parts

On branches (false stems)

Round spots 3-10 millimeters, initially light brown then dark brown.
Clearly spotted edges, gray-white center may be slightly cracked.
When the weather is humid for a long time, the center of the spot has tiny black dots — those are fungal spores.
The branches are infected with many spots and become weak, the edges of the branches become dry.

On flowers and flower buds

The petals have dark brown spots and cannot bloom.
The flower buds are dark and dry before blooming.
The flower stalks turn black, the whole bunch of flowers fall off.

This is the most costly stage — loss of flowers = direct loss of fruit.

On young and old fruits

Young fruit: small round black spot on the skin, may ooze white pus.
The fruit gradually grows larger: spots develop, indent, the skin cracks along the spots.
Fruit nearly ripe: spots spread, completely losing export value.

Seasonal Room

At the end of the dry season, March-April

Cut off all diseased branches, dry branches, and branches touching the ground. Take it away from the orchard to burn, do not throw it in the orchard.
Whitewash the base of the pillar to a height of 60-80 centimeters to eliminate pathogens.
Organic fertilizer 8-10 kilograms per cylinder and potassium sulfate 200-300 grams per cylinder. Plants that are healthy in the rainy season are less likely to get sick.
Spray the background once with *Mancozeb* (broad-spectrum manganese-zinc fungicide) or *Copper oxychloride* (copper-based fungicide).

The beginning of the rainy season in May-June

Spray once with *Azoxystrobin* (strobilurin-based fungicide) or *Difenoconazole* (triazole-based fungicide) when the plant begins to flower.
Watch the weather carefully. When there is a forecast of rain lasting 3-5 days, spray the room 1-2 days in advance.
Continue to prune branches every 2-3 weeks to keep the canopy open.

The rainy season peaks in July-September

This is the most fierce stage. Need to check weekly:

Count the percentage of branches with spots in 10 random posts (10 branches per post).
More than 3 percent of branches with spots is a sign of an outbreak — spray immediately.
Spray every 10-14 days during peak season. Change active ingredients between sessions.

Late rainy season October-November

Clean up: collect fallen fruits, fallen leaves, and fallen branches. Burn away from the orchard.
Cut back the remaining diseased branches.
Spray broad spectrum once at the end of the crop.

Protocol for treating disease outbreaks

When there was an epidemic in the orchard:

Step 1 — Cut and destroy the diseased part:

Cut all branches with clear spots. No regrets.
Discard diseased flowers and young fruits — you can't save them, the more you leave them, the more they will spread.
Bring it far from the orchard to burn.

Step 2 — Disinfect tools:

Scissors, saws, and pruning knives are washed with 70% alcohol after cutting each diseased post.
Wash your boots and gloves with diluted lime water before moving to another pillar.

Step 3 — Spraying according to regimen:

First time: *Azoxystrobin* high dose within label range.
Second time after 10 days: *Difenoconazole*.
3rd time after 10 days: *Tebuconazole* (triazole-based fungicide, different mechanism).

Rotate 3 different active ingredients between sprays to reduce the risk of fungal resistance.

Step 4 — orchard Improvement:

Pruning branches increases ventilation.
Apply 200 grams of potassium sulfate per cylinder.
Spray leaves with calcium and boron to increase tissue hardness.

Follow up every 7-10 days

[ ] Count the percentage of branches with spots in 5-10 representative pillars.
[ ] Condition of flower buds and young fruits.
[ ] Low, damp areas in the orchard — be especially careful.
[ ] Weather — number of rainy days, humidity, night dew.
[ ] Signs of mushrooms on branches touching the ground.

Common mistakes

Confusing anthracnose with black spots: using the wrong active ingredient, low effectiveness. See distinction table item 1.

Spraying the same active ingredient multiple times in a row: the fungus becomes resistant to the drug in 2-3 crops. Mandatory rotation.

Skip cleaning at the end of the season: spores on dry branches and fallen fruit = source of infection for the next crop.

Planting too thickly: over 1,100 pillars per hectare, the canopy is thick, the humidity is high, and anthracnose is strong. Suitable density is 800-1,000 pillars.

High nitrogen fertilization during the rainy season: pushes the tree to produce young branches, fungi love young tissue.

Take notes

Date of room spraying and active ingredients used.
Outbreak: date, location, percentage of infected branches.
Efficiency of processing batches.
Weather outbreaks.

References

*Prevention of diseases on dragon fruit* — Southern Fruit Institute, 2023.
*Dragon fruit export technical manual* — Department of Crop Production, 2022.
*Disease management in tropical fruit trees* — Plant Protection Institute, 2021.