The 17 essential elements
Form used by plants:
H3BO3, B(OH)4- (at high pH)
H3BO3 is the dominant form in soils thought to be absorbed by higher plants.
Regulates metabolism of carbohydrates
Activates certain dehydrogenase enzymes
Aids in formation of pollen tube and feeder roots
Involved in translocation of Ca, sugars, and plant hormones
Facilitates the synthesis of nucleic acids
Essential for cell division and development
Ideal foliage range for apple leaves:
Below normal levels <20ppm
Excessive levels >80 ppm
Ideal fruit range (tentative):
Whole fruit samples at harvest: deficient levels are < 10 mg/kg (ppm); excessive levels for Jonathan, McIntosh >25 ppm and for Delicious and G. Delicious >60 ppm; others are intermediate
Ideal soil range:
B is mobile in soils
Note: B can be easily leached from acid sandy soils. Boron availability is lowest between soil pH 7-9. Lime induced B deficiency is possible.
Fruit and blossom content are more sensitive indices of tree B status than are soil or leaf B content.
Mobility in plant:
Not remobilized within plant
Younger leaves are affected first and are often small, stiff, thick, brittle leaves with smooth margins. Main veins may be large, lacking chlorophyll, cracked, or corky (NY pub). Chlorosis and cupping are common. Leaves may form rosettes at nodes.
"Witch's broom" often occurs as sidebuds bread and start developing.
At B concentrations 12 ppm or less, terminal buds die and shoot dieback takes place. Additionally, internal bark necrosis may develop in trees deficient in B.
Ca deficiencies may appear because Ca translocation is impaired at insufficient B concentrations.
A B deficiency decreases the rate of water absorption, root growth, and translocation of sugars in plants.
Fruit symptoms include:
Increased risk of B deficiencies on:
Fruit symptoms: reduced or no yield; increased internal breakdown after harvest, increased watercore development. At leaf concentrations between 60-70ppm, fruit may ripen early and fall prematurely.
Vegetation symptoms: same as deficiency symptoms.
July 13, 2004