GROWER 101: Nutrient Disorders in Greenhouse Crops

March 18, 2002 - 12:50

Pinpoint greenhouse crop problems with this first article of a two-part series identifying nutrient disorders.

Four sets of information are important when assessing the
nutritional status of greenhouse crops and developing corrective procedures.
First, determine irrigation water quality prior to developing the location. Do
this during a wet and a dry period shortly after establishing the business and
periodically thereafter, preferably annually. Based on these results, changes
in the fertilization program can be made to compensate for water-quality
problems such as high alkalinity, high EC, imbalance of calcium (see April 2002
issue of GPN) to magnesium or high levels of individual nutrients such as
boron. Second, root substrate tests should be conducted during each crop to
monitor substrate pH and EC and the availability of nutrients. Third, a foliar
analysis should be conducted to determine the levels of nutrients successfully
taken up.

If these three tests are run and properly interpreted on
schedule, it should be possible to make the required periodic shifts in a
fertilization program to avoid nutritional disorders. Unfortunately, this does
not always occur. When a nutrient disorder occurs, a fourth set of information,
visual symptomology, becomes very helpful. The following are common symptoms
associated with deficiencies and the more common toxicities of nutrients in
greenhouse crops. Look for more in the next issue of GPN.

Nitrogen Deficiency.
The older leaves become uniformly chlorotic. After considerable time, older
leaves become necrotic and drop off if abscission is possible for the species
in question. Purple to red discoloration may develop in older leaves as they
turn chlorotic in some species such as begonia, marigold and pansy.

Phosphorus Deficiency.
The plant becomes severely stunted, and at the same time, the foliage becomes
deeper green than normal. In some species, the older leaves develop purple
coloration. Older leaves then develop chlorosis followed by necrosis. Roots
become longer than normal when the deficiency is moderate.

With foliage plants, older leaves may lose their sheen,
becoming dull green followed by red, yellow and blue pigments showing through
the green, particularly on the undersides of the leaves along the veins. These
symptoms spread across the leaf. Older leaves abscise if possible. Otherwise,
necrosis develops from the tip toward the base.

Magnesium Deficiency.
Older leaves develop interveinal chlorosis. In several species, pink, red or
purple pigmentation will develop in the older leaves following the onset of
chlorosis.

In foliage plants with pinnately (netted) veined leaves,
bronze-yellow chlorosis begins at the upper margins of older leaves, progressing
downward along the veins, leaving a green, v-shape pattern at the top of the
leaf. As chlorosis progresses down the leaf, a green, v-shape of tissue remains
at the bottom. Eventually, the tip, and then the base, become chlorotic.
Necrosis follows chlorosis in the same pattern.

Iron Deficiency.
Young leaves of seedlings sometimes develop general rather than interveinal chlorosis.
In late stages, the leaf blade may lose nearly all pigment, taking on a white
appearance.

Iron Toxicity. This
disorder mainly affects African marigolds, seed geraniums, basil, cosmos,
dahlia, nasturtium, pepper, strawflower, tomato and zinnia. Marigolds develop
bronzing on recently fully expanded leaves. The bronzing consists of numerous
pinpoint spots that begin yellow and quickly turn bronze. Affected leaves
become necrotic. Older leaves on the other crops develop numerous pinpoint
necrotic spots across the blade. As the spots enlarge, they turn necrotic until
the entire leaf dies.

Boron Deficiency. Symptoms
include incomplete formation of flower parts such as fewer petals, small
petals, sudden wilting or collapse of petals and notches of tissue missing in
flower stems, leaf petioles or stems. Death of the bud giving rise to branching
is followed by death of the new buds, eventually leading to a proliferation of
shoots termed a “witch’s broom.” Short internodes, crinkling
of young leaves, corking of young leaves, stems and buds, and thickening of
young leaves all occur. Chlorosis affects young leaves but not in any definite
pattern, resulting in eventual death of the root tips of short and thick roots.

Additional symptoms in foliage plants can include: brittle
stems and leaves; necrotic spots (black and sunken) on stems just below nodes;
nodal roots on vine plants that may become thick, short and abscise; and vines
that may become highly curled at the nodes.

Boron Toxicity. The
margins of older leaves become necrotic with a characteristic, reddish-brown
color. Necrotic spots may also develop across the leaf blade but tend to be concentrated
at the margins.

Molybdenum Deficiency. Symp-toms
apply to poinsettia, the only greenhouse floral crop it is known to affect. The
margins of leaves at the middle of the plant become chlorotic, presenting a
silhouette appearance and then quickly becoming necrotic. Symptoms spread up
and down the plant. These leaves may also become misshapen, resembling a
half-moon pattern with some crinkling.

 

This article was reprinted with written permission from
Priva Computers Inc.

About The Author

Paul V. Nelson is a professor of horticulture with the Department of Horticulture Science at North Carolina State University, Raleigh, N.C. He may be reached by phone at (919) 515-1191 or via E-mail at paul_nelson@ncsu.edu.

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