Nutrient deficiencies: what leaves show — with a symptom ranking tool

Savvas Pastopoulos, Agronomist MSc — Pastopoulos Agronomic P.C., Neos Mylotopos, Pella, Greece

A yellow leaf does not say which element is missing. It says where the symptom sits, how it is distributed across the blade, and how sharp the boundary is between the green and the yellow — and from those three things comes a hypothesis, not a diagnosis. What follows explains the mobility rule on which visual diagnosis rests, shows the three cases where that rule collapses in fruit trees, provides a tool that ranks candidate deficiencies from the symptoms, and explains why the last step is always the analysis.

1. Why leaves speak — and when they lie

When a nutrient runs short, the function that depends on it stops first. Because every element has a different role — magnesium is the centre of the chlorophyll molecule, boron takes part in the cell wall, zinc in internode elongation — each deficiency leaves a different fingerprint [2]. That is the theoretical foundation of visual diagnosis.

The problem is that the fingerprint is not unique. The formal list of limitations, as Montana State University sets it out, has six points [2]:

List of limitations after McCauley and co-workers [2].

Sources: 2 6

2. The mobility rule

The one piece of information that makes visual diagnosis possible is the position of the symptom on the tree, and the reason is purely physiological.

Some elements move within the plant through the phloem. When they start to run short, the tree withdraws them from the old leaves and sends them to the new ones, sacrificing old tissue to keep the new growth going. The symptom therefore appears first on the old, lower leaves. Other elements, once built into a tissue, never leave it again. The tree cannot recycle them, so the new growth is left exposed and the symptom appears on the young, upper leaves [2] [1].

Classification after McCauley and co-workers [2]. The exceptions that apply specifically to fruit trees are analysed immediately below.

Sources: 1 2 7

3. The three exceptions that break it in fruit trees

The handbooks in circulation are written mainly for arable crops. Three of their rules do not transfer to tree fruit, and all three concern exactly the elements that are most often short in Mediterranean orchards.

First: manganese appears on the old leaves

The general rule places manganese among the immobile nutrients, so it expects the symptom on the young leaves. In fruit trees, however, the handbook of the three Pacific Northwest universities is explicit: "usually only older leaves are affected", and only in very severe deficiency does it extend to the young leaves as well [7]. Anyone looking for manganese at the top of the tree will not find it.

Second: boron is mobile in fruit trees

Here the exception comes with a mechanism. Boron is, according to Brown and Shelp, the element whose mobility varies between species more than that of any other nutrient: in many species it is practically immobile, in others it circulates freely [9]. The division is not arbitrary. In species that produce polyols in their leaves, boron forms complexes with them and travels normally in the phloem [10].

Third: calcium cannot be read from the leaf

Calcium travels exclusively in the transpiration stream, in the xylem, and is not redistributed. The fruit, however, transpires very little and loses that capacity early, while the leaf transpires at full power until the end. Leaf calcium does not predict fruit calcium. In fruit trees, calcium deficiency shows almost always in the fruit — bitter pit, cracking, softening — and rarely gives a clear picture on the leaf. The subject is analysed in the article Calcium and its importance for plants (in Greek) and, specifically for sweet cherry, in Calcium and postharvest physiology in sweet cherry.

Sources: 7 9 10

4. The five symptom types

Every nutrient deficiency, regardless of element and species, expresses itself through five forms [1] [2]. Recognising the form is the first step, before the question of which element is at fault is even raised.

Classification after Colucci [1] and McCauley and co-workers [2].

The distinction that decides most cases

In Mediterranean orchards the commonest picture is interveinal chlorosis, and the question is almost always "iron or manganese?". There is a criterion that works:

Distinction after Benson and co-workers [7] and McCauley and co-workers [2].

Sources: 1 2 7

5. What each element looks like in fruit trees

The table below describes symptoms as they appear on fruit trees, not on arable crops. Where the picture differs by species, the species is named.

The descriptions come from the handbook of Washington State, Oregon State and University of Idaho [7], supplemented by the Montana State University series [2]. They do not constitute a diagnosis. The same symptom appears differently by species, cultivar, severity and season.

Sources: 2 7

6. The ranking tool

The tool below takes the position and the type of the symptom, together with any additional features observed, and returns a ranking of candidate deficiencies with a relative score. Each result comes with what needs to be checked in order to confirm it.

Sources: 1 2 3 7

7. What else looks like a deficiency

This is the section that makes the difference between a correct decision and an expensive one. The causes below give pictures identical to nutrient deficiencies and are, in Mediterranean orchards, commoner than several real deficiencies.

Herbicides

There is a visual criterion that separates the two chloroses. Herbicide chlorosis gives a bright yellow to white blade with sharply defined, vivid green secondary veins. Nutritional chlorosis gives a gradual fading of the green towards the midrib, without that sharpness in the secondary veins [3].

Salinity and toxicities

The non-nutritional causes

• Root disease and waterlogging. The tree cannot take up the nutrients that are present. It gives chlorosis, stunting, wilting. The key is the spatial pattern: individual trees or patches, not a whole zone.
• Viruses and phytoplasmas. Mosaics and rings that do not follow the mobility rule, often on a single branch.
• Spring frost. It gives pictures confused with both a deficiency and herbicide injury [3].
• Soil compaction, drought, excess water, insects [2].

Sources: 2 3 4 7

8. The chlorosis paradox — when analysis does not help

The natural next move after a visual suspicion is a leaf analysis. For one element, however — and unfortunately exactly the one that is most often short in the Mediterranean — leaf analysis does not work.

Iron deficiency on calcareous soils does not result from low iron in the soil but from the plant's impaired acquisition and use of the metal; the main culprit in the Mediterranean is the bicarbonate ion. It is estimated that 20 to 50% of fruit trees in the Mediterranean basin suffer from iron chlorosis [6].

The same conclusion arrives from the practical side: Washington State University notes that total leaf iron shows little correlation with uptake, and that the best indicators are the visual symptom and the soil pH [5]. Two independent sources, one research and one applied, arrive at the same place.

What works instead

• Soil pH and active lime. The most reliable predictor, and it is checked before planting, while a tolerant rootstock can still be chosen [6].
• Visual scoring or SPAD. Scales of 0 to 5, or a transmittance measurement at 650 and 950 nm that quantifies chlorophyll [6].
• Flower analysis. The most important development: it is done in spring, early enough for a correction to work. In peach, an iron concentration in the flowers below 160 mg/kg dry weight is associated with a high probability of chlorosis later. An even more stable indicator is the K:Zn ratio in flowers at full bloom: above 450 chlorosis is likely, below 375 unlikely [6].

Sources: 5 6 8

9. Leaf analysis: when, how, and the critical values

What it answers and what it does not

Distinction after Sallato [5] and Penn State Extension [8]. Note that crop size markedly affects the values: an excessive crop reduces the percentage of potassium and increases calcium and magnesium [11].

The sampling rules

• Timing: from mid-July to mid-August, when concentrations are most stable. Earlier, the tree is actively transporting nutrients into the leaves; later, it is withdrawing them [8].
• Which leaf: a recently mature leaf from the middle of a shoot or spur carrying no fruit, from mid-canopy [5].
• How many: 60 to 70 leaves, with no more than two per shoot [8].
• Uniformity: one cultivar, one rootstock, one soil type, one age. Never mixed [8].
• Comparison: where there is a problem, two samples — one from healthy and one from symptomatic trees [8].
• Frequency: every block at least once every three years. In practice: divide into thirds and sample one third each year [8].
• Washing: not needed for macronutrients. When boron, copper, manganese or zinc are to be measured, the leaves are washed in water with a little detergent and rinsed twice in distilled water [11].

Critical values for the main species

The values below apply to recently mature leaves sampled in July–August, as a percentage of dry weight for macronutrients and in mg/kg for micronutrients.

Sufficiency ranges from the Penn State Tree Fruit Production Guide [8]. The values are indicative and do not constitute a fertiliser recommendation. They apply to that specific sampling methodology; a different date or leaf type gives different values. The nitrogen range is deliberately broad because it depends on tree age, cultivar and the intended use of the fruit.

Sources: 5 8 11

10. The order of the steps

Visual observation is the first step, not the last. The sequence below keeps the cost low and the probability of error low as well.

1. Record before anything else. Which species and cultivar, where in the block, on what topography and soil type, when the symptom first appeared, on which leaves. The locations are flagged or logged with GPS and monitored [2].
2. Spatial pattern. A zone, an edge, scattered trees or the whole block? That single observation rules out half the hypotheses before any analysis begins.
3. History. Sprays over the last three weeks, herbicides own and neighbouring, irrigation, crop load, what happened at the same spot last year.
4. Visual hypothesis. Position, form, vein-to-blade boundary. This is where the tool in section 6 comes in.
5. Check the fruit and the cambium. For boron and calcium the information is not in the leaf. For shoot dieback, the colour of the cambium.
6. Analysis. Leaf for most elements, soil for pH and active lime, fruit for calcium. A paired healthy–symptomatic sample. Never within 15 days of a micronutrient spray.
7. Interpretation by an agronomist, with the data of that particular block in front of them.
8. Intervention, if one is warranted. And a repeat analysis the following year to see whether it worked.

Sources: 2 8

11. The key points

12. Sources

The numbers in the text refer to the list below.

• [1] Colucci, I. How To Diagnose Plant Nutrient Deficiencies Using Leaf Symptoms. SoilNOW, Cornell University College of Agriculture and Life Sciences, 2022. Source for the five symptom types and for the general principle of diagnosis from the position of the symptom. It is also the origin of the slip in the classification of magnesium corrected in section 2.
• [2] McCauley, A., Jones, C. and Jacobsen, J. Plant Nutrient Functions and Deficiency and Toxicity Symptoms. Nutrient Management Module No. 9, 4449-9, Montana State University Extension, 2009. Main source for the classification of mobile and immobile nutrients, for the dichotomous identification key, for the six limitations of visual diagnosis, for the separation of iron from manganese by the vein-to-blade boundary, and for the intermediate mobility of zinc.
• [3] Doohan, D., Dami, I. and Bordelon, B. Herbicide Injury and the Problem of Spray Drift. ANR-0137, Ohio State University Extension, 2023. Source for herbicide symptoms that mimic nutrient deficiencies: glyphosate with short internodes and arrow-shaped leaves, diuron with vein chlorosis, simazine with blade chlorosis and green veins, the delay of up to two weeks in symptom expression, and the spatial signature of droplet drift as against volatilisation.
• [4] Hosier, S. and Bradley, L. Guide to Symptoms of Plant Nutrient Deficiencies. Publication AZ1106, The University of Arizona Cooperative Extension, 1999. Source for the methodology of visual diagnosis, for the limitations when more than one problem is present, and for the distinguishing feature of salinity: marginal browning separated from the green tissue by a slender yellow halo.
• [5] Sallato, B. Leaf Tissue Analysis. WSU Tree Fruit, Washington State University, updated June 2021. Source for what leaf analysis does and does not answer, for the 15-day wait after a foliar spray, for the interpretation of a leaf–soil disagreement as an uptake problem, and for the finding that total leaf iron does not correlate with iron uptake.
• [6] Pestana, M., de Varennes, A. and Faria, E.A. (2003). Diagnosis and correction of iron chlorosis in fruit trees: a review. Food, Agriculture & Environment 1(1):46–51. Source for the estimate that 20 to 50% of fruit trees in the Mediterranean basin suffer from iron chlorosis, for Römheld's "chlorosis paradox", for the absence of correlation between leaf iron and the degree of chlorosis, for the role of the bicarbonate ion, for the unsuitability of the sampling date, and for flower analysis with the 160 mg/kg iron threshold and the K:Zn ratio of 375–450.
• [7] Benson, N.R., Woodbridge, C.G. and Bartram, R.D. Nutrient Disorders in Tree Fruits. PNW 121E, Pacific Northwest Extension Publication — Washington State University, Oregon State University and University of Idaho, 1994. The main source for symptoms specific to fruit trees: manganese on the older leaves, boron showing first in the fruit, the whiteness of the cambium that separates boron from winter injury, the "wither tip" of copper, magnesium as an apple problem with premature leaf drop, boron symptoms in plum and cherry, boron toxicity along the midrib, apple measles from manganese below pH 5, and arsenic toxicity in old orchards.
• [8] Orchard Nutrition: An Overview. Penn State Extension, with tables from the Penn State Tree Fruit Production Guide. Source for the sufficiency ranges for apple, pear, peach and cherry, for the July–August sampling rules, for contamination by fungicides containing manganese and zinc, for the precedence of leaf analysis over soil analysis with the exception of liming, and for the warning value of multi-year monitoring.
• [9] Brown, P.H. and Shelp, B.J. (1997). Boron mobility in plants. Plant and Soil 193:85–101. Source for the finding that boron varies in mobility between species more than any other essential nutrient, and that its retranslocation determines the expression of deficiency and toxicity symptoms.
• [10] Brown, P.H. and Hu, H. (1996). Phloem Mobility of Boron is Species Dependent: Evidence for Phloem Mobility in Sorbitol-rich Species. Annals of Botany 77(5):497–505. Source for the mechanism: in the genera Malus, Pyrus and Prunus, which produce sorbitol, boron moves freely in the phloem as a boron-sorbitol complex, while in species with little or no sorbitol it remains immobile.
• [11] Beutel, J., Uriu, K. and Lilleland, O. Leaf Analysis for California Deciduous Fruits. In: Soil and Plant Tissue Testing in California, Bulletin 1879, Division of Agricultural Sciences, University of California. Source for the leaf sampling methodology in deciduous fruit trees, for the need to wash leaves when micronutrients are to be measured, for the finding that leaves sprayed with micronutrients are not worth analysing, and for the effect of crop size on element concentrations.
• [12] Database of approved plant protection products and biocides, plantprotect.gr, with data from the database of the Greek Ministry of Rural Development and Food, and the register of approved fertilisers. Source for checking plant protection approvals and fertiliser marketing authorisations before any application.