RAIN DURING WATER STRESS – How to prevent losing flower buds?
RAIN DURING WATER STRESS – How to prevent losing flower buds?
In flower-induction techniques for sensitive fruit trees such as durian, mango, rambutan, etc., the water-stress stage is a critical step to shift the plant from vegetative growth to flower bud differentiation. However, in real production, many growers face an unfortunate situation: just a few days after starting water stress, it rains.
If not handled promptly, the sudden increase in water can break the “dry stress” condition, causing the tree to return to vegetative growth, leading to loss of flower buds, delayed flowering, or even total failure of the flowering process. Therefore, knowing how to respond to rainfall during the water-stress stage is key to preserving flower buds and keeping the tree on the right flowering track.
In durian, controlled water stress increases the concentration of hormones that promote flower differentiation (ABA – abscisic acid) and strongly reduces shoot growth hormones (GA – gibberellin). When it rains, this balance is disrupted. Rainwater combined with lower temperatures makes the tree “misinterpret” conditions as favorable for vegetative growth, triggering new shoots that directly compete with flower buds for nutrients and hormones.
Flower buds may enter dormancy due to rapid changes in moisture and temperature. They do not degenerate, but they stop developing even if water stress is reapplied. If this lasts too long, buds may convert into vegetative shoots.
During water stress for flowering, the tree’s metabolism is suppressed and physiology shifts toward reproduction. Both roots and shoots are being “held back,” and the tree is switching from leaf growth to flower preparation. But when rain occurs: soil moisture suddenly increases → roots absorb water strongly → cytokinin and GA rise → shoots are reactivated. Healthy roots send strong signals to push shoot growth again. Fine root tips may emerge 12–24 hours after rain, followed by shoot flushing after 3–5 days.
Even if growth inhibitors or bud-inducing sprays were applied, the incoming water can “unlock” the tree back to vegetative mode. The result is root and shoot flushing, flower buds are lost, and the whole flowering attempt may fail. Therefore, it is necessary to lock both roots and shoots immediately after rain to preserve flower buds. This requires combining foliar sprays and root-zone control so signals are synchronized and vegetative growth is suppressed effectively.
To preserve flower buds after rain, two actions are mandatory:
(1) Lock the roots to prevent new root flush, and
(2) Lock the shoots and axillary buds to prevent shoot flushing.
Locking roots to prevent new root growth after rain
First, wait until the soil partially dries. If the orchard is low-lying, drain standing water quickly. When soil is still saturated, roots are water-logged and nutrient uptake is weak; applying potassium at this time can easily cause root burn.
Apply K₂SO₄ (potassium sulfate, “white potassium”) at a relatively high dose to create mild salt pressure in the root zone, making it difficult for new roots to emerge and maintaining the “water-stress for flowering” condition.
Dosage must be adjusted based on tree age and vigor:
Trees with many surface roots → easier to suppress → use lower dose.
Trees without surface roots → need slightly higher dose.
Do not overapply, or roots may burn, trees weaken, and later flowering and fruiting management becomes difficult.
Locking shoots and axillary buds to prevent shoot flushing
Use high-phosphorus and high-potassium formulations (growth-inhibiting mixes), possibly combined with mild inhibitory fungicides such as Hexaconazole if necessary to enhance shoot suppression.
The goal is to age and harden leaves, stop axillary bud swelling, and send a “stress signal” from leaves to roots so roots fully stop growing.
Adjust dosage according to leaf condition:
Young leaves → slightly increase dose.
Mature leaves → normal dose.
Monitoring 3–4 days after rain
Observe carefully:
Shoot tips: If axillary buds are not swelling → locking was successful. If buds swell strongly and leaves turn lush green → re-apply growth suppression once more (reduce dose by 20–30%).
Flower buds: Round, plump, translucent → good bud preservation. If sunken into the branch or dark → nutrients are shifting to shoots → high risk of shoot flushing → must suppress again.
Roots: Dig and check. If no new white feeder roots appear → correct stress status. If slight root flush is still seen → apply another suppression round.
Do not stubbornly continue water stress when axillary buds are swelling strongly and shoot tips are already emerging. In that case, allow a light vegetative flush for 15–20 days, let leaves mature quickly, then restart flowering treatment.
Avoid having excessive nutrients in soil before flower induction. Nutrient-rich soil plus rain will trigger immediate shoot flushing. During the last 1–2 flush cycles before flowering, fertilizer must be carefully controlled: deficiency can be corrected, but excess nutrients cannot be removed from the soil.
When trees are suddenly wetted during water stress, flower buds often stop developing or become locked due to imbalance of moisture, nutrients, and internal hormones. At this point, growers must not only restore mild stress to reactivate differentiation, but sometimes must also break dormancy if buds remain “asleep” despite water adjustment. Correct timing and proper dormancy-breaking measures determine whether the tree continues flowering or shifts to vegetative growth.
Early intervention is needed when more than two of the following signs appear:
Flower buds formed but remain unchanged for 7–10 days.
Bud color turns dark brown or mossy green; bud bases thick but no elongation.
Shoots tend to emerge at branch tips instead of leaf axils.
Continuous rain and high humidity; old young leaves become glossy green again — indicating GA increase.
Suppress shoot growth
Return the tree to a “mild dry” state to prevent new flush:
Stop irrigation completely for 2–3 days after rain (if soil remains moist).
Improve orchard ventilation, drain ditches, dry soil surface faster.
Reduce shading and increase sunlight to naturally lower GA levels.
Redirect the tree toward flowering
Apply foliar sprays (preferred due to fast effect):
Phosphorus + Potassium + Boron + Calcium + secondary and micronutrients → stabilize cell membranes and fix flower buds.
Light doses of amino acids and humic acid → support metabolism without triggering shoots.
Avoid high nitrogen or magnesium and “hot” nitrogen sources, which easily induce vegetative flush.
Strengthening buds after reactivation
When buds start growing uniformly:
Supplement K + Ca + B to strengthen peduncles and reduce bud drop.
Light foliar amino acids help stabilize bud development.
Maintain controlled “dry–moist–dry” cycles so buds continue along the flowering pathway.
Conclusion
Rain during water stress is unavoidable in durian cultivation, but it can be managed if growers understand the mechanisms of bud loss and bud locking and respond in time. The goal is not to avoid rain at all costs, but to return the tree to mild stress, stabilize hormone balance and nutrition so flower buds can continue developing.
When buds remain stagnant or show signs of shifting toward vegetative growth, timely dormancy-breaking can unlock axillary buds and save the entire flowering cycle. Closely monitoring moisture, buds, and shoots during the 7–10 days after rain is the key to preventing failure and ensuring synchronized, timely flowering according to technical plans.
Technical Department – Sitto Vietnam Co., Ltd.
