Biology Reference
In-Depth Information
Weed-Killer Injury
There has always been some unintentional injury
to neighboring plants in the use of weed killers of
the kill-all variety on driveways; but since we
have had 2,4-D as a selective weed killer for
lawns, the damage to innocent bystanders has
been enormous, not only from spray drift and
volatile material in the atmosphere but from
using for other spraying purposes equipment
that has applied 2,4-D. It is impossible ade-
quately to clean out such a sprayer; mark it with
red paint and keep it for weeds only. Symptoms
of injury are curling, twisting, and other distor-
tions; there is often a fern-leaf effect instead of
normal-size foliage (
Fig. 7
). I have seen roses
seriously malformed when a factory several hun-
dred feet away mixed up some 2,4-D. I have seen
tall oaks with all leaves unrecognizable after
powdered 2,4-D was applied to the lawn. I have
seen chrysanthemum in a greenhouse utterly
deformed when 2,4-D was used on a lawn out-
side. Fortunately, unless the dose is too heavy, the
plants gradually grow back to normal.
Fig. 7
Weed-Killer Injury; Tomato and Oak
Winter Injury
Most winter browning of evergreens is due to
rapid evaporation of water in sudden warm or
windy spells. Copious watering late in the fall,
a mulch, and windbreaks are helpful for broad
leaf evergreens, as is spraying them with a waxy
material, Wilt-Pruf, which prevents evaporation.
Sudden icestorms cause obvious breaking in
trees; in boxwood and similar shrubs they result
in bark sloughing off and gradual dieback for
months, even years afterwards. I have seen symp-
toms on azaleas long after the ice was forgotten.
Zinc Deficiency
Little Leaf of almond, apricot, apples, grape,
peach, plum. Foliage is small, narrow, more or
less crinkled, chlorotic at tips of new growth, with
short internodes producing rosettes of leaves.
Defoliation progresses from base to top of
twigs. The method of supplying zinc depends
somewhat on the fruit. Spray apples, peaches,
plums, pears during dormant period with zinc
sulfate. Swab grape vines immediately after win-
ter pruning.
Mottle Leaf
of citrus. Leaves are small,
pointed, with a sharply contrasting pattern of
green along midrib and main laterals and light
green or yellow between veins.
Yellows
This term is used for some deficiency disease but
also for various virus diseases and Fusarium wilts.
