Florida and California lead in the application of nutritional sprays on
citrus and other fruit[7]. Vegetables, too, respond remarkably
thereto[8]. I see no reason why nut trees likewise should not benefit
from them, especially when other spray materials are used. Copper
sulphate, zinc sulphate, manganese sulphate, magnesium sulphate, iron
sulphate, cobalt sulphate and borax are all compatible with each other
and with most other spray materials. Combination sprays seem to perform
better, anyway, than single sprays, and the only objection would seem to
be that some element is applied that is not deficient. It can be taken
for granted, however, that nothing is wasted, even though the benefits
may be invisible. Soils benefit in the long run from sprays. One
element, even though not noticeably needed, may make another available
or it may antidote toxicity of some element present to excess. Indirect
results in all likelihood are always obtained.
In Florida, recommendations for spray applications to citrus are made
annually[9]. They can be obtained from the Florida Citrus Commission,
Lakeland, Fla. A typical formulae is as follows:
_
3-5 lbs. zinc sulphate |
3-5 lbs. manganese sulphate | per 100 gallons of water or
2-5 lbs. copper sulphate with | other spray material
equal amounts of lime. _|
1 gallon of lime sulphur or 1-1/2 lbs. of lime is used for every 3 lbs.
of sulphate of manganese or zinc.
Cherries, apples, plums are quite responsive to such applications, and I
have seen the defoliation of prune trees in New York State corrected
with a mixture containing:
_
Manganese 10% | All as metallic, in the form of hydrated oxides,
Copper 10% | and applied at the rate of 4 lbs, for the combination
Zinc 5% | material per 100 gallons.
Boron 1% _| The addition of 2 lbs. lime is optional.
In California a manganese deficiency has been observed on English
Walnuts[10], and 5-15 lbs. commercial manganese sulphate was used per
100 gallons of water during late May, through June, to correct this.
Sprays should be applied at ten day intervals until the deficiency
symptoms no longer persist.
Plausible reasons for the somewhat quicker action of sprays than
fertilizers may be furnished by two prominent authorities:
McCollum[11], one of our foremost nutritionists, first noted the
discovery that the leaf of the plant is a complete food, and that none
of the storage organs of plants, seeds, tubers, roots, fruits enjoy that
distinction. In the leaf, biological processes are most active. It is
the site of synthesis of proteins, carbohydrates and fats. The leaf is
rich in actively functioning cells which contain everything necessary
for the metabolic processes, and they supply all the nutrients which an
animal requires. ("All flesh is grass").
Hoagland[12], another authority, writes on this subject thus:
"It is now certain that soils are not invariably capable of
supplying enough boron, zinc, copper and manganese to maintain
healthy growth of plants. This knowledge has come mainly during the
past ten years. Within this period thousands of cases from many
parts of the world have been reported of crop failure, of plant
disease, resulting from deficiencies of micro nutrient elements....
The statements do not imply that most soils are deficient in any of
these elements, but the areas involved are large and important
enough to warrant the view that the recognition of micro nutrient
deficiencies constitutes a development in applied plant nutrition
of major significance.
"When I refer to deficiencies of boron, copper, manganese, or zinc,
it is not a question of absolute deficiency in total quantity of
the element present in the soil, but rather a physiological
deficiency arising from the insufficient availability of the
element in the plant; in other words, not enough of the element
can be absorbed and distributed in the plant for its physiological
needs at each successive phase of growth."
Nutritional sprays under such circumstances may prove the remedy, and we
have experimental evidence to support this. Nut trees as is shown by the
above mentioned experiment, may respond to spray applications equally as
well as citrus, other fruit and vegetables, and effects, too may possess
special diagnostic values, showing the need of trees, and therefore also
the need of soils on which they are grown.
Investigators are constantly confronted with determining whether foliage
shows symptoms of disease or starvation, and whether this is due to a
deficiency or an excess of any particular nutrient; whether fungicides
inhibit the generation of fungi from the spore state, or whether the
plant is fortified from sprays or dusts to become disease resistant, or
repellent.
Fungicides are valueless where plant disease is caused by bacteriae
which invade the water conducting tubes, (roughly corresponding to the
blood vessels of mammals), of plants, tree trunks, etc. and prevent the
flow of water and nutrient solutions from roots to leaves. Deprived of
water and nourishment, the plants or trees will wilt and die. Where,
however, soils furnish these plants with protective inorganic nutrients,
such as manganese, copper, iron, zinc, borax, etc. these bacterial
diseases are prevented. Similar actions may take place in leaves.
Deficiency Symptoms. Kodachrome Slides.
Many acute deficiency symptoms have been identified by authorities and
photographed, and I am able to show Kodachrome slides of the following:
Manganese starvation on Swiss chard, spinach (five illustrations),
courtesy of Dr. Robert E. Young, Waltham, Massachusetts.
Apricot, sweet cherry, lemon, onions, peanut, soybean (two
illustrations), tobacco (4 illustrations), sugarbeets, walnuts,
wheat, all by different authors.
Manganese deficiencies in Indiana on soyabeans, hemp, corn, by
courtesy of George H. Enfield, Purdue University.
Manganese on beets (mangels), (4 illustrations), and Romaine
lettuce, Nassau County, Long Island. Courtesy of Dr. H. C.
Thompson, Cornell University.
Many more are published in "Hunger Signs of Crops," an illustrated
reference book popular with scientific farmers and growers[13].
Other deficiencies that have been observed on nut trees are the
so-called "little leaf" or "rosette" of pecans and black walnuts[14],
which is due to a lack of zinc. Strangely enough, healthy orchards in
this case contained a preponderance of fungi, whereas in affected
orchards the soil microflora was predominantly bacterial[15].
We now have definite experimental evidence that lime, manganese and zinc
are required in appreciable quantities for the growth, health and
bearing quality of nut trees. It is well to make sure of these elements
in the soils devoted to nut tree planting, but it cannot be emphasized
too often that all essential elements and factors should be taken care
of; anyone of them may be the limiting factor in crop failure; the one
that is absent is always the most important.
In regard to inorganic nutrients, more attention has probably been
devoted to citrus trees than to any other tree species, largely because
the soils of Florida and California require additions thereof. It would
be unfair to say that such main fruit crops as apples, cherries,
peaches, plums have been neglected; we merely possess more information
on the nutrients of citrus trees than on other tree crops, as far as the
micro essential nutrients are concerned. Most orchards and groves are
fertilized only with nitrogen, phosphorus and potash, and limed when
necessary. Nitrogen can stimulate size of fruit at the expense of
quality.
A paper by P. W. Rohrbaugh[16], Plant Physiologist of the California
Fruit Growers Exchange, Ontario, California, deals with eleven mineral
nutrient deficiencies and their causes, viz: calcium, magnesium, potash,
phosphorus, sulphur, nitrogen, iron, boron, zinc, manganese, copper, and
this might well be used as a guide for nut trees.