Agriculture Reference
In-Depth Information
tips, may die and the older leaves, which show the symptoms first, may shed.
In pear the interveinal tissues on both sides of the midrib may develop as dark
purplish islands surrounded by chlorotic bands while the leaf margins remain
green. Fruits may drop early. Excessive Mg can result in the appearance of Ca
or K deficiency symptoms.
Manganese (Mn)
Manganese deficiencies tend to occur on soil with a high lime content, also
where there is a high water table or very light soil. Chlorosis between the
main veins and extending towards the midrib is typical. Manganese toxicity
is commonly found on very acid soils. It is characterized by the development
of 'measles' in which pimples erupt on the bark of
-year-old shoots. These
pimples enlarge and erupt over the years, producing sunken areas surrounded
by callus. The sunken areas then coalesce, the bark becomes rough, cracked
and scaly and the branch may die.
Iron (Fe)
Iron deficiency is most prevalent where the lime content of the soil is high or
where a drainage problem exists. The youngest leaves on Fe-deficient trees are
very pale between the veins, ranging from pale green to white, but the veins
remain green or become green even if initially paler. Dieback of shoots and
branches may occur. Excessive Fe, though rare, can result in Mn deficiency.
Boron (B)
The fruits of boron-deficient apple and pear trees are misshapen with dark
green depressed areas underlaid by hard corky tissue which turns brown on
exposure to air. Cork may also develop inside the fruit. Apple fruits may crack,
especially if Ca content is also low. Sometimes a multiplicity of small cracks
may callus over, giving a russeted appearance. Shoot tips may die and weak
new shoots emerge from below the tips. Leaves on B-deficient trees are dark
green, thick and brittle and shed early. In pears the wilting and death of
blossoms (blossom blast) may indicate B deficiency. This may also contribute
to the development of 'measles' on apple shoots. Excessive B can result in early
maturity and short storage life in apples.
Copper (Cu)
The first symptom of copper deficiency is necrosis of the terminal leaves of
actively growing shoots in mid-summer. In pear the leaf tips turn black; in
