Prevention of black spot disease (rust, rust) for dragon fruit

Black spot (Neoscytalidium dimidiatum) is a "hidden" disease on white + red flesh dragon fruit. Instructions for recognizing 4 types of symptoms, prevention from cleaning to spraying at the right time for Binh Thuan + Long An region.

Summary: Black spots (rust, rust) on dragon fruit is a disease caused by the fungus *Neoscytalidium dimidiatum*. Severely damaged orchards can reduce output by 30-50% + fruit quality cannot be exported. This article does not cover all dragon fruit diseases but focuses on black spot — the most common disease today in Binh Thuan, Long An and Tien Giang.

Applies to: White-fleshed dragon fruit (Malay variety), red-flesh (Long Dinh 1 variety). Regions of Binh Thuan, Long An, Tien Giang, Vinh Long.
Duration: Room all year round. High pressure May-October (rainy season).
Difficulty level: Medium.
Estimated additional costs: 3-6 million/ha/year of regular rooms.

Agent + method

*Neoscytalidium dimidiatum* is a saprophytic + parasitic fungus on plants. On dragon fruit:

Attack branches (false stems), flower buds, young fruits, old fruits.
Grows strongly when humidity > 85% + temperature 25-30°C — rainy season in Binh Thuan and Long An.
Spreads through rain, wind, pruning tools, people walking through the orchard.
Spores live 6-12 months on dry branches + pods fall to the ground.

Other than pepper dying quickly (plant death), black spots do not kill the plant but:

Fruit with black spots = cannot sell at a good price.
Many diseased branches = weak tree, reduced yield of the next crop.
The orchard is heavy for many seasons = the value of the orchard gradually decreases.

Four types of symptoms + how to differentiate

On branches (false stems)

Small spots 2-5mm, initially dark brown, then turn black.
Spots can be deeply sunken, branch surface rough.
The branches are severely bent and dry.

Distinguishing from other diseases:

White spot fungus (*Botryosphaeria*): white spots, no deep depressions.
Twig burn due to sunlight: red + dry, no round spots.

On flowers + buds

Buds are dark, dry, and fall off.
Flowers have spots on their petals, do not bloom or bloom incorrectly.

On young fruit

Small black spots on young fruit skin.
The spot develops into a dent + turns black.
The fruit is distorted and does not develop evenly.

On old fruit

Round spots 5-15mm, dark black, concave.
The peel of the fruit is cracked + sap may flow around the spots.
The fruit is completely devalued for export, only sold on the market at low prices.

Count the percentage of fruit with spots in the harvest. If > 10% = poor room. Need to adjust the process right from the next crop.

Room — four layers of protection

orchard cleaning

Cut off all dry branches, diseased branches, and branches touching the ground → carry them away from the orchard to burn.
Clean up fallen fruit + fallen leaves around the pillar. Mushroom spores live in fallen fruit pods for 6-12 months.
Lime the pillars + roots 2-3 times/year — at the beginning of the dry season, at the beginning of the rainy season, at the end of the rainy season.
Prune branches for ventilation — too thick orchard = high humidity = strong fungus growth.

Prune branches properly

Dragon fruit needs to be pruned periodically:

Hold 30-40 main branches/pillar.
New branches appear on the parent branch — prune if too thick.
Disinfect scissors between posts (70% alcohol or 5% javen solution).
Cut close to the main stem — don't leave the base of the branch blunt (fungus enters through blunt cuts).

Spray the room seasonally

Early dry season (November-December):

Spray the foundation once with Mancozeb + Copper oxychloride.
Lime removal.

Beginning of the rainy season (April-May):

Spray once with Difenoconazole or Azoxystrobin before heavy rain.

Peak of rainy season (June-September):

Check weekly. When you see 5% of branches have spots → spray immediately.
Rotating active ingredients: Azoxystrobin, Difenoconazole, Tebuconazole.
Spray every 10-14 days when pressure is high.

End of rainy season (October-November):

Broad spectrum spray cleans once.

Balanced fertilization + plant strength

Restrict protein during the rainy season. High protein = soft branches = easy mushrooms.
Increase potassium sulfate by 200-400g/head every quarter.
Add calcium + boron to make the fruit skin thick and strong.
Organic compost 8-10 kg/head/year.

Handling when there is an epidemic

Process:

1. Cut + destroy diseased part:

Cut all diseased branches without regret.
Spotted fruit → discard it completely, do not let the tree grow diseased fruit.
Bring it far from the orchard to burn.

2. Disinfect tools: scissors, saws, boots. 70% alcohol or 5% javen water.

3. Spray 3 times every 7-10 days:

Time 1: High-dose Azoxystrobin on label.
Second time (7-10 days later): Difenoconazole.
Third time (7-10 days later): Tebuconazole or copper.

Spray evenly on both sides of branches, especially in the canopy + near the base where moisture accumulates.

4. Improved ventilation immediately after treatment:

Pruning small branches in the canopy.
Cut the grass around the base.

Follow up every 7-10 days

[ ] Count the percentage of branches with spots on 10 posts × 10 branches/post.
[ ] Observe buds + flowers + young fruits — especially after 2-3 days of rain.
[ ] Check branches in the canopy + branches touching the ground.
[ ] Record weather: rain + humidity + temperature.
[ ] Count the number of spotted fruits when harvested.

Common mistakes

Only spray when spots are clearly visible: it's too late. Rooms at the beginning of the rainy season are 3-4 times cheaper.

Using the same active ingredient multiple times: resistant fungus. Rotate 3-4 active ingredients.

Abandon post-harvest cleaning: spores on fallen fruit + dry branches → post-harvest crop.

Planted too thickly (> 1100 posts/ha): thick canopy, high humidity, strong fungus growth. Standard density is 800-1000 pillars/ha.

High nitrogen fertilization during the rainy season: promotes disease, does not give good yields.

Take notes

Injection date + active ingredient + dose.
Ratio of branches/fruits with spots in each batch.
Weather outbreaks.
Materials + room costs.

After 2-3 years, you will see a clear pattern — which outbreak, in which area, after what type of rain.

References

*Prevention of diseases on dragon fruit* — Southern Fruit Institute, 2023.
*Dragon fruit production for export — technical manual* — Department of Crop Production, 2022.