Defoliation in nursery production: physiological aspects and the role of senication in preparing nursery stock for induced leaf drop
Producing planting material in fruit and ornamental nurseries is tightly bound to a calendar schedule. Lifting trees intended for autumn sale or winter storage must happen within a relatively narrow window, one that often arrives before natural leaf fall is complete. To keep the process efficient and preserve planting-material quality, growers use defoliation — the chemical removal of leaves. The effectiveness of this technique, however, varies considerably by species and cultivar. For crops and varieties resistant to standard defoliation, a preparatory technique has been developed — senication — which physiologically “primes” the plant for the upcoming treatment.
Defoliation: a technological necessity and a physiological mechanism
Defoliation in nursery production solves several practical problems:
Meeting deadlines. It allows lifting to begin within the optimal agrotechnical window, rather than waiting for natural leaf fall, which can be drawn out considerably in some species and cultivars.
Preserving moisture. Removing the leaves prevents excessive transpiration and desiccation of the nursery stock during lifting, sorting, transport and temporary storage.
Sanitary protection. Removing the leaves also removes much of the disease inoculum — fungal pathogens overwintering on the leaf blades.
Physiologically, defoliants act as inducers of premature leaf senescence. The chemicals penetrate leaf tissue and trigger artificial ageing. Under a defoliant’s action, a layer of abscission cells forms at the base of the petiole — exactly mirroring the anatomical sequence of natural leaf fall. The key hormonal mediator of this process is ethylene: most effective defoliants are either ethylene donors (such as ethephon) or stimulate the leaf’s own endogenous ethylene synthesis.
Modern nursery practice uses various chemical compounds for defoliation: calcium cyanamide, magnesium chlorate, ammonium sulphate, and specialised products based on copper chelates. Treatment is carried out 12–20 days before the planned lifting date, giving the plant enough time to shed its leaves physiologically.
The problem of varietal selectivity
Chemical defoliation is not equally effective across the board. Different species — and even different cultivars within a species — show markedly different responses to defoliant treatment.
Practical observations in nurseries show that, for example, apple cultivars Gala and Golden Delicious respond strongly to defoliation, losing up to 95% of their leaves. Cultivars such as Idared, Gloster and Pinova, by contrast, show a considerably weaker response to the same treatment. A similar picture is seen in other fruit crops: plum defoliates at 92–99%, cherry at 75–90%, pear at only 55–72%, and sweet cherry at just 25–35%.
International experience confirms this pattern. Studies conducted across a broad range of deciduous nursery crops found that defoliants such as S,S,S-tributyl phosphorotrithioate give good results on apple, pear and sweet cherry, but are completely ineffective on peach, apricot and Japanese plum.
The causes of this varietal selectivity lie in several factors:
Hormonal status. Different genotypes have different baseline levels of endogenous phytohormones (auxins, cytokinins, ethylene) and different receptor sensitivity to exogenous signals.
Anatomical features. Leaf cuticle thickness, stomatal density, vascular bundle architecture and abscission-layer structure at the petiole can differ substantially even between closely related cultivars.
Phenological status. The speed of entry into natural dormancy and the intensity of assimilate outflow from the leaves vary with cultivar and seasonal conditions.
Senication as a preparatory stage
For crops and cultivars showing resistance to standard defoliation, a preparatory physiological technique has been developed: senication. The idea is to apply, 1–2 weeks ahead of the defoliant treatment, a product that induces controlled artificial ageing of the tissue. Spraying nursery stock with Foliart Senicant two weeks before defoliant application, for example, promotes formation of the abscission layer and eases subsequent leaf drop.
Senication is fundamentally different from both desiccation (harsh drying) and defoliation itself. It does not cause immediate leaf death — it merely accelerates metabolism and triggers the natural senescence cascade. As a result, a number of physiological changes take place in the plant tissue that make it more responsive to a subsequent defoliant treatment:
Hormonal shift. Senication agents drive endogenous ethylene production — the primary hormone of senescence and abscission. By the time the defoliant is applied two weeks later, the plant’s hormonal system is already “primed” and ready to form the abscission layer.
Metabolic mobilisation. Senication agents activate hydrolysis of stored polymers (proteins, starch) in leaf tissue. Nutrients flow back into the stem and root system, leaving the leaf metabolically depleted and more vulnerable to the defoliant.
Structural preparation. Abscission-layer cells begin forming at the base of the petiole; under the defoliant’s action these rapidly complete their development, ensuring a clean leaf drop without tearing.
A two-stage treatment protocol
For problematic cultivars, the following protocol is recommended:
Stage one (senication). 12–14 days before the planned defoliation, apply a senication agent — a product that induces artificial ageing, such as Foliart Senicant. The goal of this stage is to launch the plant’s natural senescence programme and prepare the abscission layer.
Stage two (defoliation). Two weeks after senication, apply a standard defoliant at the recommended concentration. On a physiologically primed plant, the product works significantly more effectively: the percentage of leaf drop increases, while the risk of phytotoxic damage to buds and bark decreases.
In Polish and German nursery practice, this kind of two-stage protocol is used for apple cultivars with reduced defoliant sensitivity, as well as for stone-fruit crops, traditionally considered difficult to defoliate chemically.
Conclusion
Defoliation is an integral part of modern planting-material production technology. Its effectiveness, however, is not uniform across species and cultivars, which calls for a differentiated approach. For crops resistant to standard defoliant treatment, preparatory senication is a physiologically sound and technologically effective technique. The two-stage “senication + defoliation” protocol synchronises leaf drop, improves planting-material quality, and minimises the risk of plant damage — delivering a stable yield of marketable nursery stock even for the most difficult cultivars.
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