Prevention of root rot and pus leakage on durian by managing water and root collar

Pustule root rot (Phytophthora palmivora) is the number 1 cause of durian tree death in the Southwest. Prevention is better than treatment — the lesson focuses on water management, root collar and regular room spraying.

Summary: Every year in the Southwest durian orchard, a few trees die from root rot. The disease is caused by the algal fungus *Phytophthora palmivora* — attacks underground from the roots and then up to the root collar. By the time you see the trunk leaking pus, the tree has lost 50-70 percent of its roots, making it difficult to save. This article focuses on prevention — three disease-causing conditions can all be controlled with daily care.

Applies to: Ri6 durian, Monthong, Thai Dona durian in the Southwest (Tien Giang, Ben Tre, Vinh Long), Southeast.
Duration: Room all year round. High pressure May-October (rainy season).
Difficulty: Advanced.
Estimated additional costs: 3-6 million VND per hectare per year for periodic rooms.

Why is Phytophthora difficult to treat but preventable

*Phytophthora palmivora* is not an ordinary mushroom — it is an algal fungus (in the same group as *Phytophthora capsici* that causes rapid death of pepper). Features:

Zoospores swimming in water: heavy rain = fungus penetrates the roots with water.
Small wound attack: root collar cracks, scratches from weeding, holes from borers.
Destroy the roots first and then move up the trunk: the tree may have lost 30-40 percent of its roots before seeing pus leaking.
Lives in the soil for 3-5 years as dormant spores: the orchard once had a disease that easily recurred.

The characteristic of "attack underground + spread through water" makes Phytophthora difficult to treat once it is clearly detected. The room has 3 noses:

Water management — no waterlogging, no shock.
Protect root collar — no damage.
Spray preventively regularly — break the fungal life cycle.

Three disease-causing conditions and their control

Condition 1 — Waterlogged soil

Fungi need water to move and penetrate. The soil orchard is filled with air, slightly flooded locally = Phytophthora nest.

Control:

Dig a drainage ditch 60-80 cm deep and 40-60 cm wide between the rows of trees.
The mop is 60-100 centimeters above the highest water level of the year.
Clean ditches before the rainy season — don't let grass and leaves block the flow.
After heavy rain of 100 millimeters or more, check to see if the ditch drains quickly.

Condition 2 — Root collar injury

The wound at the root collar is the entrance for the fungus. Common wound sources:

Hoe the grass close to the root — the hoe blade scratches the root neck.
Stem borers, root collar borers.
Cracks caused by tree drying-watering-drying.
Injury when fertilizing (sprayed straight on the root collar).

Control:

Do not hoe grass within a radius of 50 centimeters around the base of the tree. Pluck by hand or use selective herbicides.
Fertilize 60-100 centimeters from the base, not close to the stem.
Check periodically for stem borers — extrusion of mites is a sign.
Cover the roots with dry grass and rice husks (leaving 15 centimeters of root collar) — reduce moisture fluctuations.

Condition 3 — Pre-existing pathogen

orchard without sprouts = no outbreak even if conditions are favorable. But:

Spores are available in the soil from the previous orchard.
Spores spread from neighboring orchards through water and soil to take root.
Pre-infected seedlings from the nursery.

Control:

Buy seedlings from a certified nursery.
Disinfect tools between orchards.
Regular spraying — breaks the life cycle of fungi in the soil.
Growing biological auxiliary plants *Trichoderma* — antagonistic microorganisms against Phytophthora.

Spray the room periodically

Spray schedule

Beginning of the rainy season (April-May):

Scan *Phosphonate* base (*Fosetyl-Aluminum* base) radius 50-80 centimeters, depth 5-10 centimeters.
Dose: 3-5 grams of treatment per liter, 3-5 liters of solution per business plant.
Or combine *Metalaxyl + Mancozeb*.

Middle of the rainy season (July-August):

Repeat scan with different active ingredients — *Metalaxyl + Mancozeb* if using Phosphonate for the first time.
Rotate to avoid drug resistance.

End of rainy season (October-November):

Final scan *Phosphonate*.
Add *Trichoderma* 200 grams per plant after scanning.

Suitable active ingredients

Phosphonate-based fungicides: *Fosetyl-Aluminum* (common trade name Aliette). Highly efficient, moves through the plant through xylem and phloem. Prevention and mild treatment.

Phenylamide-based fungicides: *Metalaxyl*, *Metalaxyl-M* (Mefenoxam). Good treatment but easy to resist — combine with *Mancozeb*.

Biological group: *Trichoderma* (probiotic product) — not a fungicide but antagonistic to Phytophthora. Use as a supplement, not a substitute for treatment.

Original scanning technique

Mix the treatment with water according to the label.
Scan evenly around the root, not concentrating in one place.
Scan radius equal to tree canopy — roots spread as wide as canopy.
Cool afternoon, no hot sun.
After 7 days of scanning, do not apply chemical fertilizers — avoid reactions.

Early detection of disease

Early symptoms

Local yellow leaves on one side of the tree: the roots on that side are attacked. A leaning tree shows that the roots on one side are dead.
The plant wilts slightly at noon, recovers in the afternoon: roots have reduced water absorption function.
Dig and check the root collar to see brown bruises, possibly pus leaking.

Symptoms of development stage

Red brown pus on the stem, especially the root collar area + stem 50-100 cm above the ground.
Widely yellow leaves, falling a lot.
The plant wilted all day, watering couldn't save it.

Severe symptoms

The tree is dead and dry.
The entire root is dark and smelly.
The body is cracked, pus flows out a lot.

Principle: detecting symptoms early can save 70-80 percent. Delayed detection can only save 20-30 percent.

Treat plants with symptoms

Early Symptom Tree

Step 1: quarantine. Mark the tree with colored string. Disinfect tools.

Step 2: scrape the pus leak on the body (if any). Apply *Phosphonate* + water mixture at a density of 10-15 grams per liter.

Step 3: high dose root scan *Phosphonate* or *Metalaxyl + Mancozeb*. Radius 50-80 centimeters, 5-7 liters of solution.

Step 4: improve drainage around the base — dig a secondary trench if necessary.

Step 5: repeat scan after 14-21 days. Change active ingredients.

Step 6: apply organic fertilizer + Trichoderma after 30 days to restore soil.

The tree is heavy (a lot of pus leaks, more than half of the roots die)

Low rescue rate. Economic decisions:

Continue to treat if the tree is still valuable (large tree, orchard with few diseased trees).
Dig out if many diseased plants + high cost. Dig holes treated with lime + Trichoderma, leave empty for 6-12 months before replanting.

Monitor periodically

[ ] Check the root collars of 3-5 random plants every 3-6 months. Dig gently and observe.
[ ] Monitor drainage ditches before, during, and after the rainy season.
[ ] Observe local leaf yellowing — early signs.
[ ] Detect a leaning tree — check the roots on that side.
[ ] Pustules on the body — check monthly.

Common mistakes

Only handle when pus leaks are clearly visible: the tree has lost 30-40 percent of its roots. Early treatment is 3 times more effective.

Fertilizing close to the root causes damage to the root neck: creating a door for fungi to enter.

Hoeing grass close to the root: damage to the root collar. Use hands or herbal treatment.

Spraying on leaves instead of roots: fungus is in the soil, not in the canopy.

Skip drainage ditches: Local waterlogging after heavy rain is an ideal environment for mushrooms.

Take notes

Room scan schedule — date, active ingredient, dose.
Discovered plants — location, symptoms.
Treatment done + results after 30, 90 days.
Condition of drainage ditches after heavy rain.

References

*Managing Phytophthora in tropical fruit trees* — Southern Fruit Institute, 2023.
*Prevention of durian latex blight* — Plant Protection Department, 2022.