CITRUS AND SUBTROPICAL FRUITS

Presented via Trans Texas Videoconference Network

Cross listed as:

HORT 422 (Texas A&M University-College Station)
PLSS 4390 (Texas A&M University-Kingsville)
PLSS 6390 (Texas A&M University-Kingsville)

Fall Semester 2004

LABORATORY EXERCISE NO. 5 MINERAL DEFICIENCIES

OBJECTIVES:

1. To become familiar with the appearance of citrus and subtropicals suffering from nutrient deficiencies.

2. To become aware of the consequences of untreated nutrient deficiency symptoms in commercial groves.

Because soils in the Lower Rio Grande Valley are highly fertile, mineral deficiencies are relatively rare, especially in comparison to the sandy soils of Florida. However, trees in Texas may sometimes show deficiencies of Fe and Zn, the former due to the element being tied up in calcareous soils, the latter due to lessened root development and activity during the winter and spring.

Nutritional deficiencies can generally be diagnosed by careful observation and without resort to leaf analysis except when multiple deficiencies create patterns which are not easily recognized.

Slide illustrating biuret toxicity in citrus

Slide illustrating salinity-induced effects in citrus

KEY TO MINERAL DEFICIENCY SYMPTOMS IN CITRUS

A1. Symptoms originating only in new growth, but often persisting in mature growth.

B1. Leaves uniform in color; growth reduced; interposed shortened giving a bushy appearance.
C1. Leaves usually large and dark green ; often boat-shaped. Shoots long and willowy in early stages; may have short and bushy secondary growth following dieback of long shoots; leaves may elongate and resemble peach leaves; gum blisters may form along vigorous shoots at base of each petiole; multiple buds or sprouts may form at the nodes; fruit may show gum in tips of locules and a brownish eruption on the peel surface termed exanthema.................................................... Cu

C2. New leaves pale green, turning yellow-green as they enlarge; growth sparse; fruit lacking or few in number, pale in color.... N

C3. New growth drab green, lusterless, sparse, with some misshapen leaves; fruit with gum deposits in the albedo; excessive shedding of young fruit; aborted seeds...................................................................... B

B2. Leaves with chlorosis patterns.
C1. Leaves reduced in size, pointed, narrow, with sharply contrasting bright yellow mottling on green background; fruit small and pale...................................................................... Zn

C2. Leaves approximately normal in size and shape.

D1. Pale green mottle over entire leaf ; mottle may be horseshoe shaped with open end toward midrib, or mottle may be a marbled pattern with dark green color following a crooked network of veins, light green in between.................................................................. Mn

D2. Feather-like straight green veins on a light green or yellow background; in severe cases leaves may be totally yellow, reduced in size and twigs may die back at the extremities...................................................... Fe

A2. Symptoms originating on mature leaves, with young leaves appearing normal or nearly so (mobile elements).
B1. Pattern formed by fading of chlorophyll in localized areas with gradual expansion in time.
C1. Fading of chlorophyll starts in basal part of leaf between mid-rib and lateral leaf margin; spread is usually outward leaving a green wedge pattern at the base of the leaf; however, it may be inward and cause a yellow wedge; entire leaf may fade to a golden bronze and abscise prematurely................. Mg

C2. Fading of chlorophyll starts along lateral leaf margins and moves inward about half way to the midrib with an irregular front; affected leaves abscise rapidly; tree growth stunted due to inadequate root system....................................................Ca

C3. Fading of chlorophyll starts as blotches in distal portion of leaf; blotches pale yellow at first but deepening to bronze as they spread and coalesce; leaf tips turn brown; old leaves persistent (in contrast to Ca deficiency); foliage drab; tree excessively droughty; fruit greatly reduced in size but of good quality......................................................... K

C4. Chlorophyll fading in randomly distributed spots on the leaf blade; spots develop brown centers with yellow or orange halos; spots may overlap or coalesce; spots from 1/4 to 1/2 inch (6.3-12.6 mm) in diameter; appearing only in fall......................................................... Mo

B2. Fading of chlorophyll not localized.
C1. Fading of leaf to dull green and eventually to orange-yellow; in extreme cases, burned tips or spots may develop; fruit coarse or spongy, hollow-centered and excessively acid; peel excessively thick.......................................................... P

C2. General pale green or yellow foliage with whitish veins; fruit sparse with pale internal and external color; quality good but juice sparse............................................................................ N

EXERCISE:

Color pictures of nutrient deficiencies are either in the TTVN section of Aggie Horticulture on the Internet or available in a reference book at your location. Review the pictures so that you become aware of the depicted deficiencies as well as the use of the above key.

QUESTIONS:

1. Select two soils from the Hidalgo Soil Survey on which Citrus is planted. Give such information as:

Name of the soil

Depth of soil in which citrus roots would be expected to thrive.

Soil texture

Fertility

Permeability

Water holding capacity (inches / inch)

Which form of irrigation would you recommend? Why?

Give reasons for your selection

On which of the 2 soils would you recommend for citrus? Why?

2. List those deficiencies that are commonly observed in Texas. In California. In Florida.

3. List those soil, plant, and environmental factors which might have an impact on the observance of deficiency symptoms.

4. At what periods might a nitrogen deficiency of citrus be most critical?

References:

Davies, F. S. and L. G. Albrigo. 1994. Citrus. CAB International. Wallingford, UK. pp. 144 - 157.

Embleton, T. W., H. J. Reitz and W. J. Jones. 1973. In: Reuther, W., L. D. Batchelor, and W. H. Chandler, (eds.). The Citrus Industry. Rev. ed. 3:122-182.

Hume, H. H. 1957. Citrus Fruits. MacMillian Co. New York. Chapter 5.

Hidalgo County Soil Survey