| Herbicide damage can be hard to diagnose. A
trained individual can generally tell when damage
from an herbicide is a possible cause, but validation
requires a laboratory test of the plant tissue and/or
the soil while the chemical is still present. Such tests
can cost between $65 and $150 per sample or more.
Individual tests need to be made for each suspected
herbicide. Testing may not be available for some
herbicides. More commonly, a circumstantial case is
made after a thorough examination of the damaged
plant(s), surrounding plants, the pattern of damage,
the likelihood of damage occurring given the
suspected point of herbicide application, and the
history of the symptoms. More information on herbicide damage and testing.
Symptoms and Diagnosis
General symptoms can include one or more of the
following symptoms: curling or cupped leaves,
stunted growth, discolored leaves, or leaves with
dead spots. The same herbicide may cause different
symptoms on different plant species.
Since herbicides do not leave a "calling card" like
mites, insects, and diseases (but the damage they
cause can be mistaken for herbicide damage), it is
advised to rule these out first. Other disorders that
produce symptoms that can resemble herbicide
damage include virus diseases, adverse weather, salt
damage, drought, soil compaction, misapplied
fertilizers, root stress, and nutrient deficiencies.
Excluding these as causes requires close
examination of the site and attention to patterns. Is
the pattern of damaged plants consistent with
drifting spray? Is more than just one kind of plant
affected? Did the symptoms appear within one or
two days (in most cases) of the suspected
application of an herbicide? Were any lawn weed
control products used in the area, including weed
and feed products containing an herbicide? The
answer to these and other questions can help make
a circumstantial case of herbicide damage.
Recovery Prognosis
Recovery of plants damaged by herbicides is
dependent upon many factors including amount of
initial damage incurred as well as what herbicide
caused the damage. Trees and shrubs that receive
minor damage from a broadleaf herbicide such as
2,4-D are likely to recover or have only minor
damage. Trees and shrubs that have been damaged
by dicamba which was applied to a lawn area and
then was washed down into the root system of trees
and shrubs can show damage for several years as
they gradually recover. Plants damaged by soil
sterilant herbicides are the least likely to recover.
Plants that show signs of growing out of the problem
will likely recover. Plants that appear to lose vigor
may not. The survival of damaged plants can be
increased by reducing other stresses. Water during
dry periods, fertilize according to a soil test report to
increase vigor, and watch for and control any insect
or disease problems. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Herbicide damage on redbud (Cercis canadensis); uniform color of dead tissue and pattern of damage does not suggest insect or disease damage
|
|
High resolution image available.
|
|
|
|
|
|
|
All the new growth on this pine (Pinus) died after weed and feed was applied to the lawn surrounding it; tip dieback can also have other causes
|
|
High resolution image available.
|
|
