Boron Deficiency in Fruit and Nut Crops

Boron deficiency in acerola

The main symptoms of boron deficiency in acerola include:

• Stunted growth
• Apical chlorosis on leaves which turn necrotic
• Severely limited fruit production

Boron deficiency in almonds

When almond trees are deficient in boron, the young branches die back from the tip, and the development of shoots from near the base of the branch gives a “witch’s broom” effect. Other symptoms include:

• Poor nut development
• Premature fall
• Nuts turning yellowish and may later blacken
• Brown gummy areas in the nuts extruded on the surface

Boron deficiency in aonlas

Fruit necrosis has been associated with boron deficiency in aonlas. The mesocarp tissue turns brown and eventually the affected tissue extends to the fruit surface, resulting in dark areas.

Boron deficiency in apples

Boron is an essential nutrient for all plants. Fertilizing apple trees with adequate boron is necessary for:

• Flower formation
• Fruit development
• Tree growth

Boron deficiency commonly causes cracking and external cork symptoms on the fruit. This may occur even though the foliage shows no symptoms, such as rosetting of thickened brittle leaves and dieback of the growing points. Boron deficiency causes premature fruit drop, and fruit quality can be badly impaired by the cork formation. If the internal cork develops early in the season, the affected fruit will become badly deformed.

In severe cases, dead areas appear in the bark of young branches (apple measles). The bark may be rough and cracked. Boron deficiency may affect the movement of calcium from the tree leaves to other tissues. As a result, boron deficiency often is associated with "bitter pit."

Applying boron fertilizers has been shown to increase yields and improve the quality of a wide variety of crops. Apples respond well to the correct amount of fertilizers. However, applying too much boron to apples can cause toxicity, so soil testing and leaf analysis is critical to determine the extent of boron deficiency.
 

Boron deficiency in apricots

When apricot trees are boron deficient, the fruit shows:

• Severe cracking
• Internal cork, particularly round the stone
• A tendency toward premature ripening in the center

Brown, dried areas may also appear on the surface of the fruit. The leaves are narrow, brittle, and often curled at the margins. Branch dieback occurs.

Boron deficiency in avocados

Boron is a key element for proper avocado nutrition. Lack of boron can cause:

• Malformed fruit
• Necrotic spots on the fruit and seed
• Spongy stem tissue
• Poor fruit set from improper pollen tube elongation

Research has shown that boron amendments in avocado affected by boron deficiency can increase yield, increase quality of fruit produced, and strengthen root development.

Boron deficiency in bananas

Boron is the most commonly deficient micronutrient in banana plantations. Boron’s primary role in banana is to act as a key component in a number vital process such as structure integrity of cell walls, cell division, root development, and membrane permeability of potassium (K+).

Boron is necessary for:

• Proper growth and development
• Pulp consistency
• Sucker development

Incomplete expansion and unfolding of the youngest leaf is probably the most typical symptom of boron deficiency. In very severe cases, interveinal chlorosis and leaf malformation occur. The leaves may be narrow, rolled, and incompletely developed. Sucker development is likely to be very poor.

Leaf streaking

Boron deficiency first results in the development of small chlorotic streaks aligned perpendicular to and crossing the primary veins of the leaf blade. As the deficiency becomes more severe, the chlorotic streaks become longer and more concentrated, eventually extending through the leaf and, in some cases, appearing as slight protrusions on the lower surface.

Leaf streaking has been recorded in cases of boron deficiency. However, such streaks usually coalesce, forming patches, and ultimately become large necrotic patches. Boron deficiency is distinguished from sulfur deficiency by the absence of necrotic patches and the appearance of malformed leaves.

Blackening in the center of the pulp of the fruit has been observed in sand culture experiments. In the field the presence of amber colored gummy deposits (mostly towards the flower end) has also been associated with boron deficiency.

Boron deficiency in blackberries

When blackberry plants are boron deficient, the terminal buds stop growing. Numerous short branches develop below the tips.

Boron deficiency in blueberries

Similar boron deficiency symptoms have been described for both V. corymbosum (highbush blueberry) and V. angustifolium (lowbush blueberry). The first sign is the development of small necrotic lesions associated with the veins of the youngest unexpanded leaves. The lesions merge, causing the leaf to curl backwards. This is followed by terminal dieback and new shoot development. Leaf fall is likely and the remaining lower leaves become dark blue-green. Internodes are short.

Boron deficiency in cashews

The first sign of boron deficiency in cashews is the swelling of the terminal section of the stem, which is followed by a stem necrosis in the same region. Necrotic spots may occur at random over the leaf surface. The youngest leaves tend to be deformed, being narrow and curled. When the deficiency is severe, the growing point dies back and axillary shoots develop.

Boron deficiency in cherimoyas

When a cherimoya tree is boron deficient, the leaves are hard and thick, and tend to bend backwards. Initially leaves are dark green but they later show an irregular chlorosis. Longitudinal growth stops and the growing points die. Side shoots also die back.

Boron deficiency in cherries

The fruit of boron deficient cherry trees has a pale chlorotic skin that may break. Gray spots develop in the fruit. The leaves are small, cupped and often yellow with red veins. The leaf margins are corrugated. Branch dieback, which is particularly evident in the spring, is followed by lower shoot development giving rise to an excessively branched condition known as “witch’s broom." Blossoms fail to develop.

Boron deficiency in citrus

Foliar symptoms of boron deficiency on citrus are not very characteristic, and a deficiency suspected on the basis of leaf symptoms should be confirmed by fruit symptoms. The first signs appear on the younger leaves as water-soaked spots which become translucent. The veins tend to be thick, cracked, and somewhat corky. The young leaves wilt and curl, and have a dull brownish-green color without any luster. Dieback of leaf tips is common. A gummy exudate may appear on the twigs and fruit pedicels.

The fruits, which are small, shrivel and go hard on the tree. They characteristically show internal gum formation, usually in the albedo but also in the pith. Normally, the gummed spots cannot be seen unless the fruit is cut. This feature helps to distinguish the deficiency from citrus impietratura disease. The rind is thick and the fruit has a low juice content. Excessive fall of young fruit occurs, resulting in very poor yields. This may be the first sign of a boron-deficiency problem. The seeds are likely underdeveloped and the seed coat dark and shriveled.

Boron deficiency in red currants

The main symptom of boron deficiency in red currants is the shriveling and blackening of the petioles and lamina of the youngest leaves. Neighboring leaves are edged with light brown bands.

Boron deficiency in date palms

Boron deficient symptoms in date palms include:

• Growing points become moribund and ultimately die
• The youngest leaves becoming necrotic

Boron deficiency in dragon fruit

Dragon fruit is a tropical fruit that requires a well-balanced nutrient supply, including boron, for healthy growth and high fruit yield.

Symptoms of boron deficiency in dragon fruit, include:

• New growth deformities, particularly the tips of young shoots which may become distorted, withered, and eventually die
• Chlorosis, yellowing, and necrosis in the leaves, particularly at the edges
• Deformed or undersized flower petals which results in poor pollination and fruit set
• Uneven ripening, reduced size and poor quality fruits

In severe cases, boron deficiency can cause the stem of the dragon fruit plant to crack, leading to wilting, stunting, and death of the entire plant. Additionally, the fruits may be more susceptible to fungal and bacterial infections due to the weakened plant immunity caused by boron deficiency.

Preventing boron deficiency in dragon fruit

To prevent boron deficiency in the crop, it is essential to maintain a well-balanced nutrient supply and soil pH. A soil test can help determine the levels of boron and other critical nutrients in the soil. The nutrients absorbed and accumulated by the plant, as well as the nutrients that are exported in the fruits at the time of harvest, should also be taken into consideration.

Your boron fertilizer options for dragon fruit

The proper way to meet the requirement for boron in pitaya cultivation is through the application of soluble fertilizers that gradually release boron, enabling continuous compliance with the plant's demand for boron, especially during flowering periods.

When using Granubor^® for soil application, we recommend applying in the canopy projection area with sufficient moisture in the soil to promote absorption. If using Solubor^®, monthly foliar applications are recommended during the fruiting and flowering phase.

Boron deficiency in durian

Boron is an essential micronutrient for plants, including durian trees. As with other fruits, boron impacts growth and quality of the durian fruit. For example, boron positively interacts with sulfur which can help improve soil fertility and increase durian yield. Research by Mitali Mandal et al (2018), showed the interaction effect between boron and sulfur might be helpful in maintaining boron and sulfur in soil vis-a-vis in moderating some important biological indices in a most favorable state, which ultimately improved soil fertility with simultaneous increase in yield. Durian is a chloride sensitive crop and normally farmers apply sulfate of potash for potassium input. Good sulfur content in the soil enhances the production of volatile sulfur compounds in durian. This contributes to the distinct smell and taste of durian fruit.

Boron deficiency can have significant impacts on durian trees, affecting their growth, development, and fruit production. Signs and symptoms of boron deficiency in durian include:

• Poor flowering and fruit set: Boron deficiency hampers the development and functionality of reproductive organs, leading to poor pollination and fertilization.
• Abnormal fruit development: Fruit may be small, misshapen, or have uneven growth.
• Cracked or split fruits: This occurs because boron plays a role in cell wall formation and elasticity. Without sufficient boron, the fruit's skin may not be able to expand properly, resulting in these types of defects.
• Corky tissue: Durian fruit tissue appears dry, cork-like, and can negatively affect the fruit's texture and quality.
• Leaf symptoms: Durian tree leaves may exhibit chlorosis, yellowing along the edges, and eventually necrosis or death of leaf tissue. The affected leaves may also become brittle or show signs of deformation.

When boron deficiency happens in durian it can also result uneven fruit ripening (UFR) which is characterized by:

• Hardened, leathery aril
• Whitish color
• Odorless and tasteless pulp

UFR normally occurs when the fruits are about to ripen and remains invisible until the fruits are opened. D159 Monthong, D197 Musang King, and D24 varieties that have bigger pulp flesh will face a higher chance of UFR.

In addition to preventing UFR, boron encourages flower bud initiation as well as increases flower production and retention—all of which can increase fruit yield. Boron also plays a vital role in pollen tube elongation, and seed and fruit development. Boron deficiency can cause incomplete pollination.

Unfortunately, boron deficiency symptoms often reveal themselves once fruit yield has decreased. U.S. Borax recommends regular soil and tissue testing to ensure you are giving your trees an adequate supply of boron throughout their growing cycle.

Boron deficiency in figs

In fig trees that are boron deficient, the terminal bud ceases to develop, followed by the appearance of numerous axillary branches just behind the tip. The leaves are chlorotic, necrotic near the margins, and distorted. The internodes are short.

Boron deficiency in grapes

Boron deficiency in grapes commonly reduces fruit set with bunches of small seedless berries and bunches of berries of varying sizes (known as “hens and chicks”).

In severe cases of boron deficiency, no normal fruit develops. The young leaves show an interveinal chlorosis, and when the deficiency is severe they may be deformed. Internodes are short and ultimately the growing points die.

Boron deficiency in papayas

One of the earliest signs of boron deficiency is a mild chlorosis in mature leaves, which are brittle and liable to curl downwards. A white “latex” exudate may flow from cracks in the upper part of the trunk, from leaf stalks, and from the underside of the main veins and petioles. The death of the growing point is followed by a regeneration of the sideshoots, which ultimately die.

In fruiting plants the earliest indication of boron deficiency is flower shedding. When fruit develop, they are likely to secrete a white latex. Later, the fruit become deformed and lumpy. The deformation is very probably the result of incomplete fertilization as most of the seed in the seed cavity are either abortive, poorly developed, or absent. If the symptoms begin when the fruit are very small, then most do not grow to full size.

Boron deficiency in peaches

Typical boron deficiency symptoms in peach trees are small, thick, misshapen, and brittle leaves carried on branches with short internodes. A water-soaked dieback is followed by excessive branching. Veins and midribs are pronounced and are often corky and red in color. The bark may split and have pronounced lenticels.

Reduced fruit set occurs. Fruit are often small and abnormal, with internal necrotic patches and sometimes without seed. Fruit may crack.

Peaches are also particularly sensitive to boron excess. Flower bud and flower shedding can both be caused by boron toxicity.

Boron deficiency in pears

When pear trees are boron deficient, the fruit becomes misshapen with cork developing under the large depressions. The upper leaves are small and cupped. The small branches die back as the boron deficiency becomes more severe.

Boron deficiency in pecans

When pecan trees are boron deficient, small, water-soaked areas develop on otherwise normal leaves. These areas turn purplish and then a reddish brown.

As boron deficiency becomes more severe, more spots appear but they do not coalesce. The lower leaves on the rachis develop normally but the distal ones become small. Internodes are short and the growing points die back.

Boron deficiency in pineapples

Boron is a key element for proper nutrition of pineapple. Lack of boron can cause:

• Malformed fruit
• Broken core
• Separation and cracking of fruitlets
• Poor fruit set
• Reduced sugar content

Few leaf symptoms have been reported. In very severe boron deficiency cases, the growing point may die, followed by profuse development of side shoots and suckers. Root growth is poor. Main roots may be brown and few fibrous roots are produced. The deficiency is more pronounced on the ratoon than on the plant crop.

Research has shown that boron amendments in pineapple affected by boron deficiency can increase sugar content, increase quality of fruit produced, and strengthen root and slip development. Boron has also been found beneficial when adding ethephon to induce flowering.

Boron deficiency in pistachio

Boron deficiency in plums

Tip dieback and leaf fall, particularly on the upper branches, can be expected, but the main symptoms of boron deficiency in plums are formed on the fruit. Brown sunken areas appear in the flesh and sometimes gum pockets are also formed. Multiple branching is prominent at the tops of the trees. Flowering is seldom impaired by boron deficiency but as very many flowers fail to develop, there is usually a marked reduction in fruit set.

Boron deficiency in raspberries

Failure of the fruiting canes to develop normally in the spring is one of the first signs of boron deficiency in raspberry bushes. Death of buds on the canes and failure to produce normal laterals give the bush the appearance of suffering from a “dieback." Berry production in such plants is likely to be considerably reduced.

Buds that develop are likely to show distorted leaves with some edge necrosis and unusually large petioles. Pith necrosis occurs. In less severely affected buds, leaves are small, thin, and deeply indented, giving a “feathery” appearance. Leaf crinkling also occurs. The lack of development of the old canes often results in a profusion of new canes from the base of the plants which will usually carry fairly normal leaves.

Boron deficiency in strawberries

The first symptom of boron deficiency appears on the young strawberry leaves as a tip necrosis. These leaves are likely to be misshapen (often “squared off”), cupped, and reduced in size. Many small lateral buds may form in the crown but their development is very restricted. The runner plants become progressively more stunted with small, distorted, chlorotic leaves.

Boron deficiency also causes fruit distortion, probably due to incomplete fertilization. Fruits may split before ripening and corky patches may develop. The flesh has a leathery texture.

In the latest stages of boron deficiency, flowers fail to set fruit.

Boron deficiency invwalnuts

If walnut plants are boron deficient, large, irregular, necrotic patches develop between the veins, particularly on the terminal leaflets. When boron deficiency is severe, the leaves are twisted and the veins are very prominent. Dieback from tips of the shoots results in very evident leafless branches. The nuts do not set properly and a marked reduction in yield can be expected. Walnut trees do not usually need boron supplemenation until they reach bearing age (12 years).

Photo courtesy of Dr. Patrick Brown, University of California-Davis