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Foliar application

Also known as
foliar spray, foliar feeding, foliar-applied

A foliar application is the spraying of a crop input, such as a nutrient, biostimulant or crop protection product, directly onto a plant's leaves so that it is absorbed or acts through the foliage rather than through the roots.

What is a foliar application?

A foliar application puts a product onto the leaves of a growing crop, usually as a spray. Crop protection products such as fungicides and insecticides are commonly applied this way. Foliar applications are also used to deliver nutrients, a practice known as foliar feeding, and to apply biostimulants aimed at helping the crop through stress or critical growth stages.

How leaves absorb products

Leaves are built to keep water in, not to let substances through. Their outer surface is covered by the cuticle, a waxy, water-repellent layer. Dissolved substances cross it slowly, mainly through tiny water-filled pathways in the cuticle and around leaf hairs and stomata, the pores that let gases in and out. How much is absorbed depends on:

  • The product: its form, concentration and molecule size.
  • The leaf: thickness of the cuticle and wax, which varies by crop, leaf age and growing conditions.
  • Contact time: absorption stops when the spray droplet dries, so humidity and temperature matter.
  • Coverage and retention: droplets that bounce or run off, or bead up on waxy leaves, deliver less.

Adjuvants are added to improve wetting, spreading and retention on the leaf and, for some products, penetration through the cuticle.

When foliar nutrition works best

Leaves can absorb only limited quantities of nutrients, so foliar feeding cannot replace soil fertilization for the major nutrients a crop needs in large amounts. Its strengths are:

  • Correcting micronutrient deficiencies, such as zinc, manganese or iron, where small amounts have a large effect.
  • Rapid response, when root uptake is limited by cold, dry or compacted soil.
  • Targeting critical stages, such as flowering and early grain or pod fill, when demand is high.

Timing and application

Timing is often more important than rate. Foliar products are typically applied at growth stages when the crop responds most, or ahead of expected stress. Good practice includes:

  • Spraying when conditions allow droplets to stay wet on the leaf longer, such as early morning or evening, and avoiding the heat of the day.
  • Following label rates to avoid leaf burn, especially with salt-based nutrient products.
  • Checking tank-mix compatibility before combining products.
  • Choosing nozzles and pressures that give good coverage while limiting spray drift.

Foliar applications at Locus

Locus’s Bombigro is a foliar-applied biological that Locus describes as supporting photosynthetic activity, stress tolerance and crop development, applied at key vegetative and reproductive stages by ground, aerial or drone application.

Frequently asked questions

For major nutrients such as nitrogen, phosphorus and potassium, no: leaves cannot absorb enough to meet the crop’s total needs. Foliar feeding is most useful for micronutrients and for supplementing nutrition at critical times.

Generally early morning or evening, when temperatures are lower and humidity higher, so droplets stay wet longer and the risk of leaf burn is lower. Product labels may give specific guidance.

Many leaves are waxy and water-repellent. An adjuvant helps spray droplets stick to, spread over and in some cases penetrate the leaf, improving coverage and uptake.

  • Adjuvant

    An adjuvant is an ingredient added to a spray mixture, or built into a formulation, to improve how a crop protection or nutrient product performs or how the mixture handles. Surfactants, crop oils, drift reducers and water conditioners are common types.

  • Biostimulant

    A biostimulant is a substance or microorganism that, when applied to seeds, plants or the root zone, stimulates the plant's natural processes to improve nutrient uptake, nutrient use efficiency, tolerance to abiotic stress, or crop quality and yield, independent of any nutrients it contains.

  • Spray drift

    Spray drift is the movement of spray droplets or vapor away from the intended target during or after an agricultural application. It wastes product, reduces control on the target, and can harm nearby crops, people and the environment.

  • Tank-mix compatibility

    Tank-mix compatibility is whether two or more crop inputs, such as pesticides, fertilizers, adjuvants and biologicals, can be combined in one spray tank without separating, forming solids, losing effectiveness or injuring the crop.

  • Abiotic stress

    Abiotic stress is stress on a plant caused by non-living environmental conditions, such as drought, heat, cold, salinity, flooding or nutrient imbalance, as opposed to biotic stress from pests, diseases and weeds. It is a leading cause of crop yield loss.

  • Wetting

    Wetting is the ability of a liquid to spread over and stay in contact with a solid surface. It depends on the balance between the liquid's attraction to the surface and to itself, and it is usually measured by the contact angle a droplet makes with the surface.

Sources

  1. Uptake of hydrophilic solutes through plant leaves: current state of knowledge and perspectives of foliar fertilization, V. Fernández and T. Eichert, Critical Reviews in Plant Sciences, 2009
  2. Foliar fertilization, Land-grant university extension publications