Warning about root rot and collar rot disease on Aquilaria trees: Early recognition and proper treatment to avoid significant damage

Aquilaria tree is a high-economic-value forestry tree, developed by many localities to produce agarwood. However, during cultivation, one of the most dangerous diseases for Aquilaria trees is root rot and collar rot. If not detected early and treated promptly, the disease can quickly kill trees, spread throughout the garden, causing significant damage to growers.

In reality, in many Aquilaria growing areas in the Southeast region such as Đồng Nai, Bình Dương, and some other localities, the disease often appears strongly during the rainy season, especially in low-lying areas with poor drainage or gardens with improper care techniques.

How dangerous is root rot and collar rot disease?

According to the experience of many gardeners, trees from 4 years old and above begin to be susceptible to the disease. The disease often occurs at the beginning and end of the rainy season, when soil moisture is high, and fungi and bacteria thrive.

The danger lies in its very rapid destructive speed. When the tree just shows symptoms of wilting, grayish-green leaves or “sad leaves”, it can die completely within a few days to about a week.

In many cases, the trunk near the base, about 10 - 20 cm from the ground, becomes soft and rotten; a slight impact can cause the tree to fall. When excavated for inspection, the roots will appear black and rotten, emit a foul odor, or have peeling bark.

Main causes of the disease

Root rot and collar rot disease is often caused by a combination of soil fungi, harmful bacteria, and unfavorable cultivation conditions.

Common causes include:

• Waterlogged, poorly drained soil

• Prolonged rain causing oxygen deficiency in roots

• Applying fresh manure, uncomposted fertilizer

• Hard, compacted soil, poor in organic matter

• Dense, humid garden

• Garden tools carrying pathogens from other places

• Weakened trees due to nutrient deficiency or root damage

It can be said that the disease is not only caused by pathogens but also by the environment that creates favorable conditions for pathogen development.

Early signs of recognition

Growers need to regularly inspect the garden to detect the following early symptoms:

On the foliage

• Leaves slightly wilted at noon, not recovering in the afternoon

• Leaves yellowing branch by branch

• Tree canopy gradually thinning, slow growth

At the base of the tree

• Bark at the base dark, moist, cracked, or oozing sap

• Base soft, with rotten areas

• White fungi or mold around the root collar

Root system

• Feeder roots die first

• Main roots black and rotten, easily broken

• Foul-smelling, slimy

The earlier it is detected, the higher the chance of saving the tree.

The most effective disease prevention measure is from the beginning of the season

Agricultural experts recommend: for root rot disease, prevention is always more effective and less costly than treatment.

1. Prepare well-drained, elevated soil

This is the most important factor. When planting Aquilaria, it is necessary to create mounds or raised beds in low-lying areas. Dig drainage ditches around the garden before the rainy season.

Do not allow water to accumulate around the base for more than 24 hours after heavy rain.

2. Apply well-rotted organic fertilizer

Should use:

• Well-composted animal manure

• Microbial organic fertilizer

• Compost

Do not apply fresh fertilizer as it can easily introduce pathogens into the soil.

3. Supplement with Trichoderma antagonistic fungi

Trichoderma is a beneficial microorganism that helps inhibit many types of root-rotting fungi, while also improving soil and stimulating root development.

It should be mixed with organic fertilizer and applied periodically at the beginning and end of the rainy season.

4. Keep the garden well-ventilated

• Weed regularly

• Prune low branches and diseased branches

• Collect rotten leaves and diseased plant remains for disposal

The more ventilated the garden, the harder it is for diseases to develop.

5. Rational watering

Do not overwater during the rainy season. During the dry season, only water when the soil is dry. Avoid watering in the late afternoon/evening, which can leave the base moist overnight.

How to treat trees at the onset of disease?

If the first few trees are found to be diseased, immediate treatment is necessary to prevent spread.

Step 1: Isolate the diseased area

• Stop watering to prevent spread to other areas

• Limit movement from diseased areas to healthy areas

• Disinfect tools after use

Step 2: Treat soil and base

Lightly loosen the soil around the base to improve aeration. If the soil is low-lying, immediately clear drainage ditches.

Scrape off the rotten bark (if mild), let it dry, then apply medicine according to professional instructions.

Step 3: Use plant protection products according to instructions

Active ingredients commonly used to treat root-rotting fungi and bacteria include:

• Copper-based compounds

• Metalaxyl

• Mancozeb

• Validamycin

• Other specific soil fungicide treatments

It is necessary to carefully read the instructions for use, adhere to the correct dosage, proper isolation period, and prioritize consulting with local agricultural officials.

Step 4: Tree recovery after treatment

After 15 - 20 days, when the disease subsides, supplement with:

• Microbial organic matter

• Humic

• Trichoderma

• Light foliar fertilizer if the tree is weakened

Do not apply strong nitrogen fertilizer immediately after the tree is diseased.

What to do with severely dead trees?

Completely dead trees should be:

• Dug up, including the trunk and roots

• Removed from the garden for disposal

• Lime sprinkled to treat the hole

• Soil left to dry for a period before replanting

Do not replant immediately while the soil still carries pathogens.

Recommendations for Aquilaria growers

Many gardeners focus only on fertilizing and neglect the drainage system. This is a common mistake that causes widespread tree death when the rainy season arrives.

For sustainable Aquilaria cultivation, remember 3 core factors:

Well-drained soil – healthy roots – disease-free garden.

Sustainable direction

Aquilaria is a high-value tree but also requires good technical care. If root rot and collar rot disease are well-managed, people can maintain stable garden growth for many years, creating a foundation for future agarwood extraction.

In modern production, combining organic matter, microorganisms, and scientific irrigation management will be a long-term solution to reduce disease, lower pesticide costs, and enhance economic efficiency