If patterns of damage in the field planting and on the
individual plant are uniform and repeated, this indicates that a
nonliving factor is the probable cause of the damage. We will now
examine additional information and clues to determine whether the
nonliving damaging factor was a mechanical, physical, or chemical
Look for changes in the three categories of
nonliving factors of the affected plants
1) Mechanical Factors (Damage/Breakage)
plant damage caused by site changes "construction
damage," transplanting damage, "lawn mower blight",
2) Physical Factors environment or
weather changes causing extremes of temperature, light,
3) Chemical Factors chemical pesticide
applications, aerial and soil pollutants, nutritional disorders.
Close visual examination and questioning will often
determine if the stems or roots have been broken or girdled or if
the leaves have been bruised, punctured, or broken. For example,
if a large Ficus elastica is dropped while being transplanted and
the stem is broken, rapid wilting of the portion of the plant
above the break will occur. Examine the plant site for signs of
recent excavation, construction, paving, etc.
Primary sources of diagnostic information are damage
patterns and weather records to pinpoint time and location of
weather extremes. Records are "signs" of the factor that
caused the plant damage.
Heat: The highest leaf temperatures will occur
in the early afternoon when the sun is located in the southwest
quadrant of the sky. Therefore, lethal leaf temperatures produced
by solar radiation absorption will occur primarily on unshaded
leaves on the outer surface of the plant canopy on the southwest
side. Portions of leaves shaded by other leaves or leaves on the
shaded northeast side may be undamaged. Most severe damage occurs
on leaves most exposed and furthest from the vascular (roots,
stem, leaf vein) source of water, i.e. leaves on outer perimeter
of plant, leaf tips and interveinal areas. A recognizable pattern
related to leaf tissue that would have the highest potential
temperature and be most readily desiccated will occur uniformly
over all plants in the area.
Cold: Damage will occur on the least hardy
plants and will be most severe on the least hardy tissues of those
specific plants. In fall acclimation, cold hardiness is first
achieved by the terminal buds, and then with time the lower
regions achieve hardiness; the branch crotches are often the
last tissues to achieve cold hardiness. And, generally the
root systems will not survive as low a temperature as will the
tops -root systems are damaged at higher temperatures than are the
tops. On-the-other-hand, after hardiness has been achieved, if
warm temperatures induce deacclimation (i.e. in the early spring),
the terminals (buds) are first to become less cold hardy.
Portion of plant damaged will indicate if low
temperature damage occurred before plant achieved cold hardiness
in the fall, or if it occurred after cold hardiness was lost in
the spring: reverse patterns are produced.
On a given structure (i.e. leaf or bud), the damage
will be death of exposed, non-hardy tissues in a recognizable
(repeated) pattern. For example, frost damage to foliage,
i.e. conifer needles, in the spring will uniformly kill all
needles of a given age from the tip of the needle back toward the
stem a given distance on each needle.
Frost cracks are longitudinal separations of
the bark and wood generally on the southwest sides of the
trunk-most likely to occur because of daily, wide temperature
fluctuations. Freezing death of dividing cells on outer
portions of leaf folds inside the bud will cause distorted or
lace-like leaf blade because of nonuniform cell division and
growth during leaf expansion. Cold damage to the root system
is primarily a concern with container-grown plants where the root
temperature fluctuates more and can be expected to reach lower
temperatures than would occur with the same plant if field-grown.
Cold damage to the root system can be detected by examining the
roots: Damage generally occurs from the periphery of the root ball
(near the container edge) and evidence includes blackened or
spongy roots with lack of new growth or new root hairs. Above
ground symptoms generally will not be evident until new shoot
growth in the spring; at that time leaf expansion may be
incomplete (small leaf size) because of the restricted uptake of
water and nutrients by the damaged root system. With increased air
temperatures, the water loss from the shoots and leaves may exceed
the root uptake capacity; the plants may defoliate due to this
Plants Vary in their Cold Tolerance: The cold
tolerance (hardiness) of various plants in the landscape has been
rated by the USDA (see Plant Hardiness Zone Map, USDA-ARS #814).
The "indicator plants" listed for the various cold
hardiness zones on the map are useful in surveying a group of
landscape plants, observing which ones show cold damage and then
estimating how low the temperature dropped based on the
damaged/undamaged indicator plants. Differences in cold tolerance
of root systems (especially roots of plants grown in exposed
containers) are presented by Green (Ornamentals Northwest
Newsletter 12-5:3-15, 1988).
Light Extremes: Plants can acclimate to various
conditions, but the primary requirement for acclimation is time.
Plants respond adversely to rapid changes in the environment.
Rapid change from low to high light intensity will result in
destruction of the chlorophyll pigments in the leaf (yellowing and
necrosis = sunburn). Rapid change from high to low light intensity
will result in reduced growth and leaf drop; new leaves will be
larger. "Sun leaves" are smaller, thicker and lighter
green in color than are "shade leaves". Flowering will
be reduced, delayed or absent under low light.
Oxygen and Moisture Extremes: Here we are
primarily considering the root environment where oxygen and
moisture are inversely related. Waterlogging (moisture saturation)
of the root environment results in oxygen deficiency; without
oxygen, root metabolism and growth come to a standstill.
Consequently, uptake of water and nutrients is restricted with
subsequent wilting and nutritional deficiency symptoms occurring
on the above ground portions of the plant. Drought and water
logging produce many of the same symptoms on the above ground
portion of the plant: The first symptoms will be chlorosis and
abscission of older leaves. Under severe, continuing moisture
stress wilting and necrosis will occur on tips and interveinal
regions of recently expanded leaves and new growth (Figure 6).
FIELD PATTERNS OF PLANT INJURY RELATED TO CHEMICAL
Look for application, drift, or runoff-accumulation
patterns in the field (Figure 10): The pattern of
plant injury in a field or other group of plants and date of
injury appearance can be helpful in relating the damage to a
specific chemical application.
Damage diminishing uniformly from one side to the
other (Figure 10.A, Spray Drift): A pattern in a
field, yard or on a group of plants that starts on one side and
diminishes gradually and uniformly away from that area is typical
of wind-drift of droplets.
|Figure 10. Illustrations of patterns of plant damage
related to chemical applications to field or bed plantings.
|A. Drift of spray droplets.
B. Spots of injury from low temperature or accumulation of
volatile chemicals or accumulation of chemical runoff in low
areas of the field; or, injury associated with soil variables.
C. Stripes indicating overlapping application pattern, or one
or more faulty applicator openings.
D. Plant injury at end of field due to double application.
E. Definite break between injured and uninjured sections of the
planting: application discontinued or changed in applied
F. Increasing injury within an application band due to poor
mixing or inadequate chemical agitation.
Damage in individual spots or irregular patterns
(Figure 10.B): Low lying areas in a field where air masses
settle would enhance the accumulation of fumes from volatile
chemicals, would be frost pockets, and might enhance pathogens.
These damage spots might also be related to differences in the
soils texture, organic matter, pH or moisture. High pH spots might
induce nutritional disorders such as iron deficiency, increase the
toxicity of triazine herbicides, etc.
Damage in linear stripes at regular intervals,
(Figure 10.C), indicates nonuniform application of a
chemical. Regularly recurring stripes of damaged plants at
intervals within the width of the application equipment
(fertilizer applicator, pesticide spray boom, etc.) indicate an
oversized or worn nozzle, improper setting on one applicator
opening, or an overlap in application. Another cause may be carry
over of a residual chemical from bands applied the year before
-this pattern would match the row width and direction from the
Damage at ends of field, (Figure 10.D),
may be due to double application of a chemical either the year
before or the year the injury is observed.
Damage on one part of the field only with a
definite break between the damaged portion and the remainder of
the field (Figure 10.E):
1) Was the chemical applicator reloaded or recalibrated
at the break-point? If so, mistake might have been made in
chemical selected or in rate of application, or the applicator
might not have been adequately cleaned of a toxic chemical: the
toxic residue was removed in application of the first load of
chemical. Check equipment-use records.
2) Check tillage methods, dates and soil conditions
(moisture) resulting differences in soil texture or depth of
tillage may cause differences in dilution of carry over chemical
residue, differences in volatilization and dilution of an applied
Damage intensity increasing along a broad band,
(Figure 10.F), indicates inadequate mixing or poor
agitation of a wettable chemical powder in a spray tank resulting
in increased concentration of the applied chemical toward the end
of the tank load.