Among fruits, visual symptoms of calcium deficiency have only been noted in apple trees, and these in sand culture experiments.

The symptoms shown were: Death of the growing points of terminal shoots followed by die-back of the affected shoots; scorching and forward rolling of the leaf margins, the tip leaves being first affected.

Symptoms of this deficiency are most marked on the foliage, and the effects always develop initially on the oldest leaves and proceed systematically towards the younger ones. Chlorotic effects are common, which is not surprising in view of the fact that magnesium is a constituent of chlorophyll, the green coloring matter of the leaf. But chlorosis is by no means the only color effect produced, and brilliant tints are often developed. The deficiency is most prevalent towards the end of the growth seasons of plants, but it may appear in seedlings, especially in rainy periods. ( See Plate 26 ).

The usual sequence of events is that the oldest leaves are the first to develop the characteristic symptoms, which intensify either gradually or quickly, whilst simultaneously they spread progressively towards the younger leaves. Severely affected leaves may wither and be shed, or may absciss without the withering stage. Defoliation may be extremely severe, as for instance, with apple trees, where by August or September a heavy-cropping tree may be left bearing no leaves other than those on the tips of shoots and be unable to ripen the crop.

The remarkable variety of effects produced by magnesium deficiency on the leaves of different kinds of plants makes it necessary to learn the symptoms for individual plants, but when they are known, their great variety has the advantage that it enables abundant cross checking of symptoms in field diagnosis.

Where magnesium deficiency symptoms develop in annual plants at a late stage in their growth period, yields may not be appreciably reduced, but in perennials such as fruit, a prolonged deficiency results in stunted growth and eventually in a useless tree.

The deficiency has been of very rare occurrence in cereals in this country. The leaf symptoms take the form of an intervenal chlorotic striping and growth may be considerably dwarfed.

Brassicae, as a group, appear very susceptible to the deficiency, and of these cauliflower, broccoli and kale are most severely affected. In these crops the symptoms begin in a similar fashion, as an intervenal chlorotic mottling or "marbling" of the older leaves. The affected leaves later develop tints which may be very brilliant (especially in cauliflower and broccoli) yellow, orange, red and purple colors predominating. In swedes, the whole of the chlorotic areas may become reddish purple and the deficiency may be confused with phosphorus starvation.

In sugar beet, the symptoms begin as a faint intervenal chlorosis (resembling a water-soaked condition) near the leaf margins and extend between the lateral veins towards the midrib. The chlorosis subsequently increases in intensity and yellowish tints are developed. Finally, areas near the leaf margins and between the veins become necrotic, and produce a scorching effect, and the older leaves may wither.

These symptoms may be confused with those of virus "yellows" but can be distinguished from them by the patchy distribution of symptoms over the leaf and the orange tinting produced by the virus. ( See Plate 30 and Plate 110 )

Potatoes may show severe effects of the deficiency, and in this crop some variation in symptoms is shown by different varieties. The leaves may or may not show considerable chlorosis, beginning as usual at the base of the plant. Necrosis may develop either marginally and extend in a patchy fashion between the veins towards the midrib (e.g., Sharpes Express) or may occur intervenally over a well-defined central area around the midrib, leaving a clear, green, marginal band (Dunbar Standard). Affected leaves may wither quickly and hang vertically down the stem or be shed. Defoliation may be serious. One example was noted where severity in a "blight" attack (phytophthora infestans) was clearly related to areas of magnesium deficiency.

In tomatoes, the lower leaves first show intervenal chlorosis and yellow patches may occur in the chlorotic areas. The leaf margins may or may not remain green, and the leaves may show some marginal roll towards the upper surfaces. Intervenal necrotic patches develop later, and finally the leaves wither and are either shed or remain hanging vertically on the stems.

The most severe effects of the deficiency in this country have occurred on apples, the leaves of which show a variety of symptoms. In their simplest form the symptoms consist merely of an intervenal necrosis, either in areas around the midrib or beginning near the margins and developing progressively towards the midrib, The brown necrotic condition is preceded by a slight fading of the normal green color in the areas to be later affected and these light green areas also feel limp and thin to the touch. The necrosis may be preceded by purple tinting which fades as the necrosis develops, or the necrosis may be accompanied by an intervenal chlorosis. In some examples of marginal necrosis it is difficult to distinguish the symptoms from those which result from potassium deficiency.

Under acute magnesium deficiency, the fruits of apples fail to ripen normally on the trees, and are small, poorly colored and lack flavor. The leaf symptoms shown by other fruit plants are as follows:

Pears, very dark brown intervenal patches, developing first near the midrib and spreading outwards, the margin remaining green; plums and cherries, brown intervenal and marginal necrosis, with varying degrees of chlorosis; gooseberries, a broad red marginal band which eventually fades to pale yellow or cream; black currants, the leaf surface becomes a vivid purple color with the exception of a marginal band, which remains green, and the leaf tends to curl back towards the under surface; raspberries, the central portion and the margin of the leaf become yellow, with a green band separating the tinted areas; strawberries, the tinted pattern is similar to that of raspberries, but bright orange, red and purple tints are developed.

Symptoms of potassium deficiency may vary according to the extent of the shortage of the element. Thus in a mild deficiency in cereals, plants with rather thin shoots may be developed and, where the deficiency is acute, shoots may die back and stunted plants with numerous tillers but few or no flowering stems, result. In trees, a slight deficiency leads to somewhat restricted shoot growth, and the shoots are thin, whilst when severe no terminal shoot growth occurs and shoots or entire branches die back, and eventually the tree may die. Leaf symptoms are striking, and though somewhat varied are generally very characteristic for the different kinds of plants. The color of the leaves may be dull bluish-green, and there may be some chlorosis, especially in intervenal areas. One of the following symptoms will invariably occur, beginning on the older leaves; browning of the tips (tip burn), marginal scorching (leaf scorch), the development of brown spots, usually most numerous near the margins; this last symptom may occur along with marginal scorching.

The laminae of the leaves of many broad leafed plants show a tendency either to curl backward toward the under surfaces or roll forward towards the upper surface parallel with the midrib. Scorched margins often turn sharply forward.

Considerable stunting usually follows from potassium deficiency, internodes of stems are short, the production of grain and fruit is greatly curtailed and root systems may be very poor, trees often being loose in the soil.

Broad-leaved crops which show scorched leaf margins should always be suspected of potassium deficiency, but it must be pointed out that this symptom may result from other causes, such as calcium or phosphorus deficiencies, chloride injury, damage from salt spray, drought, drying winds, burning from fertilizers, etc.

Important symptoms for some of the more important plants are as follows:

In cereals, the plants are either thin and grain formation is poor, both heads and individual grains being small, or they may tiller excessively and have few flowering stems, whilst growth is soft and the leaves somewhat bluish-green or slightly chlorotic, and leaf tips and margins may show browning. Barley appears to be the most susceptible cereal.

The leaves of Brassica crops are bluish-green and may show slight intervenal chlorosis. Leaf margins show scorching and leaves may tend to curl backward, with the scorched edges curling sharply forward. Scorching may progress intervenally from the margins towards the midribs in cauliflowers. Growth is slow, and in consequence the leaves are tough and unpalatable.

In sugar beet and mangolds, the leaves may appear somewhat upright in habit. The older leaves develop marginal browning which extends intervenally towards the midrib. Finally, the scorched leaves wither and fall round the plant.

Potassium deficiency is of outstanding importance in potatoes. When severe the plants are very squat in habit. The leaves lack luster, are dull, bluish-green and may show intervenal chlorosis. The margins and tips develop browning and innumerable small, dark brown spots, which eventually coalesce, are apparent on the undersides. The upper surfaces of the leaves have a characteristic bronzed appearance. The leaves show crinkling and curling towards the under surfaces. They eventually turn brown and wither and may be shed, or the stems may collapse and the haulms lie as a brown mass on the soil. Tuber size is much reduced and crops may be negligible.

Tomato plants have a high requirement for potassium. When the element is deficient the plants are woody and growth is slow. The leaves are bluish-green in color. In the lower leaves, the green around the margins and between the veins fades to a pale grayish color, and the leaf margins eventually become scorched and curl forward towards the surface. Scorching may progress towards the upper leaves. The leaves may also show bronzing, and small, yellow and orange patches may develop on some of the leaflets. The fruits often fail to ripen evenly, and may show sharply defined, green patches near the stalks (greenback), or greenish-yellow patches, which merge into the general red color of the surface (blotchy ripening).

Clover is one of the crops in which spotting of the foliage occurs in addition to marginal browning, With this plant the leaves first show some chlorotic spotting and marginal chlorosis, and these are followed by browning of spots and margins.

Onions and leeks show as the chief leaf symptom browning of the tips, which progresses down the leaves in the manner of a "die-back". Parsnips, carrots and beans, and to a less extent peas, are often affected by potassium deficiency. Chlorosis and scorch occur on these plants, and with peas the leaves may show spotting as for clover.

The deficiency is of outstanding importance for fruit, especially apples, gooseberries, red currants and raspberries. With all, growth is stunted and dieback of shoots and branches common; the leaves are bluish-green and may show some intervenal chlorosis, and all show typical marginal scorch, either brown or gray in color; blossom buds may be plentiful in the early stages of the deficiency but fruit yields are very low and quality is of the cull grade.

On apple leaves, marginal scorching is the outstanding symptom, and there may be some intervenal chlorosis. Apple fruits may be fairly highly flushed or remain green and of immature appearance; they are sub-acid and woody to taste. In pears, the scorched margins of the leaves are almost black. In plums, peaches and cherries, there may be considerable chlorosis in addition to scorch, and some varieties show considerable forward rolling of the leaf margins, In gooseberries and black currants, marginal scorching is generally preceded by purple tinting of the leaves which disappears as scorch develops. Red currants show some intervenal chlorosis in addition to marginal scorch. Raspberries and other rubi, in addition to marginal scorching, exhibit intervenal browning.

The only crops on which sodium deficiency effects may be said to be shown are the sodium-loving crops, such as sugar beet, mangolds and turnips. Where sodium is in short supply for these plants, the leaves are dark green, rather dull, wilt rapidly in drought and many tend to grow out horizontally from the crown of the plant.

Drastic deficiency of sulfur in the field has been reported for tea, in which shoot growth becomes restricted, leaves decrease in size, become rolled towards the upper surfaces, are stiff and brittle, and show marked chlorosis and yellowing; defoliation is severe and eventually terminal buds die and branches die back. The condition is known as it "tea yellows".

Sand cultures with tomatoes and fruit plants have shown that the effects of sulfur deficiency in many ways resemble those due to nitrogen deficiency. Shoot growth becomes restricted, though less so than with nitrogen deficiency; stems are stiff, woody and thin; growth is erect and yellowing and tinting of the leaves occur. In the author's experiments brilliant orange and red tints were developed on apple, gooseberry and strawberry foliage.

Iron deficiency is much more common in fruit plants than in vegetable or agricultural crops. The main symptom is always severe chlorosis of the leaves, and young growths are always most severely affected. In some instances the leaves may be almost wholly bleached and in others the chlorosis may produce a mottled pattern. Scorching of leaf margins and tips may occur in extreme conditions.

Since chlorosis due to iron deficiency has almost invariably been associated with soils of high lime content, it is often termed "lime-induced chlorosis".

Cereals, other farm crops and vegetables are evidently very resistant to iron deficiency in the field, since they are grown even on chalk soils without showing appreciable deficiency effects.

A soil derived from the Dolomitic Conglomerate is the only one known to the author to produce iron deficiency in cereals, and here the condition is complicated by the presence of high amounts of zinc in the soil. The young plants become markedly chlorotic, especially the tops of the plants, and leaf tips die. The plants eventually become very weak, remain stunted and may die.

Brassica crops suffering from iron deficiency all show chlorotic "marbling" effects on the leaves, and occasional leaves are completely bleached. The symptoms are very similar to those of manganese deficiency, and frequently it would be impossible to distinguish between the two deficiencies on these crops from visual symptoms alone.

On tomatoes, the leaves near the tips of the plants show a chlorotic mottling, the chlorosis being most pronounced near the midrib and towards the bases of the leaflets.

In apples, pears, plums and cherries, the chlorotic symptoms are similar and definitely more severe on the young leaves at the tips of the shoots, In severe examples the shoot tips die and the die-back may extend downwards into the large branches.

Raspberries, and other rubi, are very severely affected, and chlorotic leaves may occur for considerable distances down the shoots from the tips. Gooseberries and currants are not as susceptible as raspberries or the tree fruits, and often the only leaf symptom is a slight intervenal chlorosis of tip leaves.

Strawberries may be severely affected, when the leaves show severely chlorotic intervenal areas whilst the veins remain green.

Chlorosis of the leaves is one of the most common symptoms of manganese deficiency, but the detailed symptoms are very varied.

Among cereals, oats is the most susceptible crop, and total failures from manganese deficiency are common. The deficiency in oats is known as "Gray Speck" disease. The leaf symptoms usually appear on the older leaves in the early spring, when the plants are four to six inches high. The basal portions become somewhat yellowish; gray or buff-colored specks or streaks appear, chiefly in the basal halves and often most severely near the margins. The streaks tend to elongate and coalesce, and severely affected tissue turns brown. The leaves eventually break over near the distal ends of the seriously affected basal parts. The tissue above the break may remain green and hang down limply. The brown areas may also twist into the form of spirals. In the final stage, severely affected leaves turn brown and wither. The root system is often very poorly developed and badly affected plants may die out completely. Substantial recovery may occur naturally after mid-summer, when growth may show much improvement and heads may be formed, but usually there is relatively little grain and many of the heads are "blind".

In wheat and barley the leaves are somewhat pale green and may show only faint chlorotic streaking and yellowing. On severely affected wheat plants intervenal white lesions are developed and on barley numerous small brown spots and lesions occur along intervenal areas. Affected leaves on the lower parts of the plants turn brown and die off.

In Brassica crops the symptoms first appear as an intervenal, chlorotic marbling. With severe deficiencies the whole of the leaves may be practically bleached, only the veins remaining green, as in kale, or some necrosis may develop in the mottled tissue, when it takes on a dull, brownish gray appearance, as in savoys.

The symptoms shown by sugar beet, mangolds and garden beet are very characteristic, the condition in sugar beet being known as "Speckled Yellows". The leaves tend to be more upright than usual and somewhat triangular in outline, due to curling of the margins towards the upper surfaces. In sugar beet and mangolds, the intervenal tissue becomes chlorotic, but in garden beet the chlorosis is masked by the red pigment of the leaves, although the green color disappears from the leaves and they appear a rather faded red color. The red tinting is very striking when seen in a bed of plants. ( See Plate 85 ).

Brownish spots may appear in the intervenal areas and the brown tissue may die and fall out leaving small holes.

In potatoes, the tip leaves lose their luster and turn pale, and tend to be small and rolled towards the upper surfaces. Small blackish-brown spots may be developed on the leaves along the veins, and although these are more numerous on the pale leaves near the tips of the shoots, they may also be present on older leaves which are still green.

In severe conditions the plants in the mass show much browning and yellowing, especially in the young foliage.

Of vegetable crops, parsnips show a very characteristic intervenal chlorosis; in spinach and spinach beet the symptoms are similar to those of sugar beet; dwarf beans become strongly chlorotic and the chlorotic tissue develops necrotic areas; runner beans show a mild intervenal chlorosis in Cos Lettuce the older leaves become chlorotic; parsley leaves show browning of the leaf margins; in marrows there is a striking intervene chlorotic mottling; onions develop chlorotic streaking of the leaves.

In peas, the deficiency produces a very characteristic condition of the seed known as Marsh Spot. The plants themselves may appear quite healthy or, with a severe deficiency, may show a somewhat chlorotic condition in the foliage. When the seed coat is removed and the two cotyledons separated, either a small brown speck or a larger, circular brown area seen on the flat surfaces. The areas may become hollowed out in very severe conditions.

Although acute manganese deficiency occurs in tomatoes in the U.S.A where the plants become markedly chlorotic, only very mild instance have been observed by the author. In these only the tip foliage was affected, the symptoms taking the form of an intervenal, chlorotic mottling on the young leaves, similar to that caused by a mild iron deficiency. ( See Plate 74 ).

Apples: The leaves develop an intervenal chlorosis which begins near the margins and extends towards the midrib, and finally only the veins remain green. Strongly growing young shoots may be only little affected, which is a point of difference from iron deficiency, where the chlorotic condition is always most severe in the young tip foliage.

Pears: The normal green of the leaves may appear slightly faded and a somewhat faint intervenal chlorosis develops, beginning near the margins and progressing towards the midrib. The chlorosis is very distinct from that due to iron deficiency.

Plums and Peaches: The type of symptom is similar to the apple; peaches especially may become severely chlorotic.

Cherries: The leaves show a marked intervenal chlorosis with a very definite pattern, beginning near the. margins and progressing towards the midrib.

Black Currants: The tip leaves become slightly chlorotic. Severe effects have not been observed.

Raspberries: The leaves, especially on the upper parts of the shoots, become severely chlorotic; the appearance is very similar to that due to iron deficiency.

Boron deficiency is responsible for a large number of so called "diseases". The best known of these are "Heart Rot" of sugar beet and mangolds, "Canker" of table beet, "Brown Heart" of swedes (also known as "Raan") and turnips, "Browning" or "Hollow Stem" of cauliflower, "Cracked Stem" of celery, alfalfa "Yellows", "Drought Spot" (or "Cork", "Corky Core" or "Corky Pit") of apples, "Hard Fruit" of citrus and Top Sickness of tobacco.

The list leaves no doubt as to the importance of the deficiency in crops, and also indicates the wide variety of symptoms which have given rise to the numerous descriptive names applied to the "diseases".

With many plants growing points are severely affected and may die, and stems and leaves may show considerable distortion. Both the pith and epidermis of stems may be affected, giving rise to hollow and roughened stems. Leaves are often scorched and curled, and may show slight mottling or some pigment formation. Fruits when affected are severely deformed and useless.

The deficiency is not known in cereals in the field, and they may have a very low requirement for boron.

The Brassicae, as a family, may suffer severely. Cauliflowers are particularly susceptible, the symptoms consisting of a browning of the curd (the curd may actually fail to develop), distortion of the young leaves and a hollow condition of the stem. Marrow stem kale shows some distortion and growth restriction near the growing point, a slight mottling of the younger leaf margins and a hollow condition of the stem. A crack develops in the stem at the hollow portion and infection with bacillus caratovorus may occur. Cabbages are fairly resistant; young plants may show distortion of the leaves and old plants water-soaked or breakdown areas in the pith of the stems in the region of the heads. Swedes and turnips may show no external symptoms in tops or roots, but when the roots are cut across transversely, patches of water-soaked and slightly brownish-colored tissue, surrounded by tissue of more normal appearance, may be seen occupying the central portions. With an acute deficiency the center of the root may be hollow. The roots are fibrous and somewhat bitter to taste. In one severe instance in swedes examined by the author, roughening of the skin on the upper portions of the roots occurred. ( See Plate 99 )

Very characteristic external symptoms are shown by sugar beet and mangolds. In young plants the youngest leaves show weak development and may die and become brown, when rotting of the crown follows. It older plants the outside leaves show a wilted condition, tend to lie on the ground, become severely scorched and develop yellow pigment. The upper surfaces of the petioles may show cracking of the epidermis. The growing point dies and the crown becomes covered with numerous small and often deformed leaves. The crown tissue rots and a large hollow surrounded by black tissue may be formed. The symptoms are fairly similar for mangolds, but rotting often begins on the side of the root rather than in the crown. In table beet, rotting occurs on the sides of the root and may not penetrate into the more central tissues.

Boron application has been stated to have cured an internal rust spot of potatoes but, in the author's experience, potatoes grown in the field under conditions producing total failures of sugar beet and other boron susceptible crops have not shown any symptom which could be attributed to deficiency of boron.

On the other hand, boron toxicity has been induced in potatoes by dressing of 20-lbs. per acre of borax to a soil in which the deficiency is readily induced in sugar beet by liming. The injury was shown as a brow marginal scorching ( See Plate 108 ), the brown area being very narrow.

In "cracked stem" of celery, the leaves show a brown mottling, the stems become brittle, and brown stripes appear in the epidermis above the vascular bundles of the stalks. The affected tissues later disrupt and become dark brown in color.

Boron deficiency has not been observed in tomatoes other than in sand cultures.

Although boron deficiency has not been recorded in commercial plantations of apples in this country, its effects are serious in important fruit-growing areas, such as Canada, U.S.A., New Zealand and Australia and it also occurs in some European countries. The fruits produced are malformed and misshapen. On the exteriors, they may show cracking and roughening of the skin and pitting, and internally, corky areas in the cortex and browning in the core region may occur. The trees may lose some their leaves and develop a condition of the foliage known as rosetting; defoliation and rosette symptoms are accompanied by splitting at roughening of the bark, and by die-back of the twigs and branches.

Though deficiencies of zinc and copper are of importance for several crops in various countries, these deficiencies have not been observed for any crop in this country, (England) and are thus merely of academic interest at present. A deficiency of molybdenum has not yet been recorded in a field crop any part of the world. (Since this was written, fields in China have been found to be deficient.) Zinc deficiency is considered to be the cause of several serious "diseases" of fruit trees in the U.S.A. and other countries "Little Leaf" or "Rosette" of apples, pecans, vines and stone fruits, "Mottle Leaf" of Citrus and walnut "Yellows". It also causes "Bronzing" of tung, and "White Tip" of maize, and is responsible for poor yields cereals in Australia.

Copper deficiency is also associated with certain pathological condition of fruit trees in U.S.A., South Africa and Australia, notably "Exanthema" or die-back of Citrus, pears, prunes, plums and apples, in which shoots die-back, the foliage may show "burning" of the margins or chlorosis, and resetting and multiple bud formation may occur; gumming may also take place.

The deficiency occurs in farm crops in Holland and Denmark, where it is known as "Reclamation Disease", "Yellow Tip" and '"Wither Tip", and in Australia.

Characteristic symptoms in cereals are withering and marginal chlorosis (yellowish gray) of the tips of the younger leaves, which may fail to unroll, and a tendency for the foliage to wilt; the bases of the plants remain green and bushy in appearance; grain formation is more severely restricted than vegetative growth.

In the U.S.A., on certain peat soils, copper is also essential for the proper growth of lettuce.

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