Technical solutions to restore mango trees after saline drought

After salinity drought, mango trees need to recover in the following order: wash salt, check EC, restore roots, re-nourish leaves and then add nutrients. Doing it in a hurry can cause the roots to burn, leaves to fall and another crop to be lost.

Summary: Mango trees are more tolerant of salt than durian, but will still decline severely if watered with salt water many times, especially when the tree is bearing young leaves, flowering or growing fruit. Recovery after salinity drought must go in this order: have fresh water, then wash away the saltwater, then restore the roots, nourish the leaves, and then increase fertilization. This article guides the 45-60 day process for mango orchards in the Mekong Delta.

Applies to: Hoa Loc mango, Cat Chu mango, Taiwanese mango, Acacia mango affected by mild to moderate salinity drought.
Duration: 45-60 days of main recovery, followed by 1 additional incident after that.
Difficulty level: Medium. Need to measure salt and not rush to stimulate flowers.
Estimated additional costs: 4-10 million VND per hectare for lime/gypsum, organic, humic, Trichoderma and foliar fertilizers.

Identify mangoes affected by drought and salinity

After a drought, mango trees often show the following signs:

Old leaves have yellow edges and burnt tips.
Young leaves are small, hard, and fall easily.
The buds stand still and do not develop.
Flowers dry quickly, fruit setting rate is low.
The young fruit falls off, the stem is weak.
The topsoil is white with salt or crusty after drying.

If the plant wilts at noon but recovers in the evening, the impact is still mild. If it wilts all day, leaves fall a lot and branches dry in parts, the root system has been seriously damaged.

Assessment before recovery

Don't fertilize as soon as the tree has just passed the saline drought. First you need to check:

Is the water source fresh?
Is there still salt water in the orchard ditch?
Does the soil in the root zone have high EC?
Proportion of burned canopy.
Is the tree bearing flowers/fruits or has it fallen?

If you don't have fresh water, just water sparingly so the plant doesn't wilt too much. Watering too much with salty water will add more salt to the surface of the beds.

Step 1 — Saline the soil

When there is stable fresh water:

Irrigation around the roots continuously for 3-5 days.
Irrigate 2-3 times a day, 15-30 minutes each time depending on the system.
The goal is to pull salt out of the root zone, not to water and erode the soil.
After salting, apply lime about 1 kilogram per adult tree or use gypsum if the soil does not need to raise the pH.
Water lightly to dissolve lime/gypsum and help push sodium out of soil glue.

If you have a meter, check soil EC. When EC is below about 1 mS/cm, the plant will enter a safer root recovery stage.

Step 2 — Root recovery

7-10 days after salting:

Irrigation with humic or diluted fish manure around the root area.
Apply 5-10 kilograms of decomposed organic fertilizer per tree, depending on the age of the tree.
Mix Trichoderma as recommended to limit root-damaging fungi.
Keep moderately moist, don't let the soil dry out and crack, then water thoroughly.

At this stage, high doses of NPK should not be applied. The roots are weak, applying too much can easily burn the roots and cause the tree to lose more leaves.

Step 3 — Regenerate the leaves

About 10 days after root recovery:

Spray foliar fertilizer with calcium, potassium, silicon and trace elements.
You can use additional amino acids, humic acids or seaweed to support plant recovery.
Spray in the cool afternoon, do not spray when the plant is hot and wilting.
Repeat twice, 7-10 days apart.

The leaves are the "factory" that restores the tree. When the new leaves grow evenly and turn green, the tree will be able to move on to fertilizing to increase nutrition.

Step 4 — Prune away the portion that can no longer be restored

After the tree begins to stabilize:

Cut dry branches, dead branches, cracked branches.
Do not prune the entire canopy strongly when the tree is still weak.
Large cuts require copper or lime-based paint.
If the tree is bearing fruit, prune small fruit, deformed fruit, or fruit that is about to fall.

Keeping too much fruit after a saline drought will further deplete the tree. With average tree decline, you should accept a reduction in yield for one crop to keep the tree.

Step 5 — Fertilize to increase nutrition

After 20-30 days of root and leaf recovery:

Add 5-10 kilograms of organic fertilizer per tree if the soil is poor.
Apply a light, balanced dose of NPK, divided into 2 small doses instead of a strong one-time fertilizer.
Prioritize potassium sulfate, calcium, magnesium and trace elements.
Avoid high nitrogen fertilization when the plant has just sprouted.

If the leaves are green, sprout evenly, and hairy roots appear, you can gradually return the plant to the normal care schedule.

Should flowers be stimulated immediately after drought?

Do not stimulate flowering in the first 1-2 months if the plant still shows signs:

The leaves have not recovered yet.
The branch is still dry.
The soil is still salty.
The tree just dropped its fruit/flowers.

Inducing flowers when the plant is weak often results in small flowers, low fruiting rate and further plant decline. Only handle flowering when the plant has at least one new set of completely old leaves.

Post-recovery monitoring

[ ] Salinity of irrigation water before each pump into the ditch.
[ ] Ec of soil in the root zone after salt washing.
[ ] Ratio of burnt leaves and new leaves.
[ ] Number of dry branches trimmed.
[ ] Flower/fruit loss rate if the tree is in season.
[ ] Recovery costs vs. retained productivity.

If the leaves still have yellow leaves after 45-60 days, check for root rot, nematodes or soil pH.

Common mistakes

Strong fertilization immediately after salinity drought: weak roots cannot absorb it, plants easily burn roots.

Washing salt when the water source is not yet fresh: the more you water, the more salt is brought into the orchard.

Do not drain the old ditch: the water in the ditch is still salty, not enough to wash the surface.

Stimulating flowers to "remove the crop": the plant has not yet recovered, the flowers are weak and fall easily.

Pruning branches too hard: the tree loses photosynthetic leaves and recovers more slowly.

References

*Technical solution to restore mango trees after drought* — Hainong technical document.
*Measures to limit the harmful effects of salinity on fruit trees* — National Agricultural Extension Center.
*Restoring orchards after drought and salinity* — National Agricultural Extension Center.