Phytotoxicity test procedure
 Environmental factors influencing...

Title: Phytotoxicity on foliage ornamentals caused by bactericides and fungicides
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00066894/00001
 Material Information
Title: Phytotoxicity on foliage ornamentals caused by bactericides and fungicides
Series Title: Plant Pathology Fact Sheet PP-30
Physical Description: Book
Language: English
Creator: Chase, A. R.
Simone, Gary W.
Affiliation: University of Florida -- Florida Cooperative Extension Service -- Department of Plant Pathology -- Institute of Food and Agricultural Sciences
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Publication Date: 1985
Spatial Coverage: North America -- United States of America -- Florida
 Record Information
Bibliographic ID: UF00066894
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
        Page 1
    Phytotoxicity test procedure
        Page 2
        Page 3
    Environmental factors influencing phytotoxicity
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
Full Text

Plant Pathology Fact Sheet

Phytotoxicity on Foliage Ornamentals

Caused by Bactericides and Fungicides
A. R. Chase and G. W. Simone, Professor, Retired, University of Florida, Mid-
Florida Research and Education Center, Apopka, and Professor and Extension
Plant Pathologist, Retired, respectively, University of Florida, IFAS, Gainesville.
1985 (Copied 2001)
Florida Cooperative Extension Service/ Institute of Food and Agricultural Sciences/ University of Florida/ Christine Waddill, Dean

Pesticides are routinely employed by or-
namental plant producers, and they are gener-
ally efficaceous and safe to the crop. The rigid
standards for aesthetic quality of foliage orna-
mentals place equal importance on pesticide
safety to the plant and efficacy. When new pes-
ticides become available or new crops are in-
troduced, it is wise to test the safety of each
product on each plant. Pesticides labeled for
use on a diverse plant group, such as the philo-
dendron genus, should not be assumed to be
equally safe on all species or cultivars. Even
under the normal conditions in which pesti-
cides are routinely applied, phytotoxicity (plant
injury) occasionally occurs. Phytotoxicity can
result in a variety of symptoms and may be
more severe under certain production situa-
tions. The wrong choice of pesticide, whether
due to active ingredient, carrier chemical, or rate
applied, can result in plant injury. Use on pes-
ticide-sensitive plant species, such as schefflera
(Figure 1), can result in plant injury more often
than not. The practice of tank mixing pesticides,
fertilizers, and/or spreader stickers can prove
injurious to plants as can the application of pes-
ticides during adverse environmental or cul-
tural conditions. Even miscellaneous chemicals
such as algicides and disinfestants used in the
production site, although not plant-directed,
can cause phytotoxicity (Figures 2, 3). Phyto-
toxicity can reduce plant quality and increase
time needed to produce salable plants.

Symptoms of Phytotoxicity

Phytotoxicity may express itself in a va-
riety of ways, some obvious and some subtle.
Symptoms range from minor leaf speckling to
plant death. One of the most common phyto-
toxicity symptoms is chlorosis. Symptoms gen-
erally appear on the new growth and can be
confused with fertilizer deficiencies. Sometimes
chlorosis is slight and barely noticeable while
at other times the tissue turns white within a
few weeks of application (Figures 4-8). In other
situations, the leaves remain green while the
petioles or stems turn chlorotic (Figure 9).

Another common symptom of phytotox-
icity is necrosis or burning. Burning can occur
on leaf tips, margins, interveinal tissue or sim-
ply scattered across the leaf surface. Burning is
the most obvious phytotoxicity symptom short
of plant death. Burning usually appears within
a week of pesticide application, but may take
as long as six to 6ight weeks to appear if mul-
tiple applications are required and the pesti-
cide is applied only once a month. Burning may
be caused in several ways. Contact burns are
characterized by a general speckling of the leaf
surface with spots found wherever spray drop-
lets landed (Figures 3, 10). Some burns occur at
spots on the leaf where spray accumulates and
causes localized damage (Figure 11). Other
burns occur when the pesticide is absorbed
through leaves or roots and is redistributed


(Figure 4), usually appearing on leaf margins
where the pesticide accumulates (Figure 5). Fi-
nally, some burns occur on young plant tissue
which is not fully developed at the time of ex-
posure. This damage can occur on leaf tips or
edges which were exposed, while the rest of
the leaf which was rolled remains asymptom-
atic (Figure 11).

Distortion of new growth or cessation of
growth is sometimes difficult to diagnose as
phytotoxicity unless plants are monitored
closely. Distortion of new leaves on rapidly
growing plants can occur within a week of pes-
ticide application. This symptom is occasion-
ally attributed to a viral disease since it too can
cause distortion of new leaves. Growth distor-
tion symptoms due to pesticide phytotoxicity
should be more uniformly distributed through-
out a bed or range of plants than symptoms
caused by a viral disease. Sometimes a combi-
nation of distortion and stunting occurs, which
may result in cessation of plant growth (Figure
12). Tips of some distorted leaves appear chlo-
rotic or necrotic and internodes may be short-
ened (Figures 13, 14).

Be sure that what you are calling phyto-
toxicity is indeed due to a pesticide applica-
tion. Many times fertilizer burns and even some
diseases appear similar to phytotoxicity symp-
toms. Avoid confusion by keeping accurate up-
to-date records of all treatments (fertilizer or
pesticide) which are applied to your plants.
Consult a plant pathologist if disease is sus-

Many symptoms of phytotoxicity are
difficult to verify unless some plants of the same
age and cultivar were untreated. This is the only
way to assess such symptoms as stunting, re-
duced leaf size or slight chlorosis. It should be
remembered that once phytotoxicity develops,
most symptoms will not disappear. The plants
may outgrow the problem, but leaves with
burns or distortion will not become healthy.
Phytotoxicity must be avoided since it usually

cannot be cured. The key to avoiding phyto-
toxicity is to follow the label directions and to
test the product under your conditions on your

Phytotoxicity Test Procedure

A phytotoxicity test should be per-
formed by all growers whenever new plants or
varieties are added to their product mix, they
wish to try a new product, or they are using a
new tank mix of two or more products. You
should always test pesticides on a small group
of plants prior to applying them broadscale.
The following test is a sample format which
could be used to perform a phytotoxicity trial
with a pesticide which you have not used be-

1. Select healthy typical plants of each cultivar
or type on which the pesticide will be used.

2. Read the pesticide label to determine the
application site (roots or leaves), the rate of
application (amount per gallon/liter), and the
interval of application (number of days between
applications). These facts must be determined
prior to starting the trial. Many researchers and
chemical companies W-111 their products at
double the labeled rate in order to obtain a
greater margin of safety.

3. Use clean spray equipment and perform the
test during the time of day when most of your
pesticide applications will occur.

4. The key to a phytotoxicity trial is to have one
control set of plants which are sprayed with
water only. If the pesticide is normally applied
with a spreader sticker, include a set of plants
to receive an application of spreader sticker in
water since adjuvants such as spreader stick-
ers can cause phytotoxicity as well as the ac-
tual pesticide. These two sets of plants will be
the ones which you compare to pesticide-
sprayed plants for signs of damage. Control
plants must be sprayed under the same condi-

tions as pesticide-sprayed plants.

5. Wait two to three weeks before determining
that a pesticide is safe. In this period of time
most severe phytotoxicity will become appar-
ent; however, plant stunting will not be appar-
ent for a longer period of time. If stunting ap-
pears to be a problem, the test must be con-
ducted for several weeks and the pesticide re-
applied at the labeled interval. In general, these
trials will identify only severe phytotoxicity
such as chlorosis and necrosis of leaves.


The desire to save time and money may
lead to the common practice of tank mixing sev-
eral fungicides or a fungicide with other pesti-
cides such as miticides, insecticides or
nematicides. Some fungicides are formulated
with special spreading agents that can result in
plant injury if indiscriminately tank mixed with
a second spreader sticker product. Although
some pesticide combinations are quite safe for
use on many plants, others can cause plant dam-
age. Some situations exist where pesticides are
additionally mixed with soluble fertilizers in
the interest of greater labor efficiency or due to
availability of application equipment. These
situations can also result in phytotoxicity.

A number of general observations apply
to the tank-mix situation. In choosing among
formulations of the same product, select wet-
table powder (WP) formulations over emulsi-
fiable concentrate (EC) types since the latter are
more likely to be phytotoxic and more prone
to incompatibility problems because of emul-
sion sensitivity. The combination of WP with
EC formulations or soluble fertilizers may re-
sult in breakdown of the emulsifying agent, de-
pending on pesticide concentration and water
quality, and hence phytotoxicity and loss in ef-
ficacy. Water soluble pesticides (i.e., Acti-dione,
Agri-Strep, Aliette, Banol, or Subdue) can usu-
ally be mixed with any number of insoluble
pesticides. Streptomycin-based pesticides

should not be used with EC formulations. If two
water soluble pesticides must be tank mixed, a
reduction in rate up to 50% for each compound
may be needed to avoid phytotoxicity since
both pesticides compete similarly for chemical
bonding sites with water. Finally, avoid tank-
mix combinations for strongly acid and alka-
line materials which can result in chemical in-

A number of pesticides offer safe tank-
mix labeling or some label indications of prod-
uct compatibility. For other pesticide combina-
tions (with or without fertilizers), trial and er-
ror is required in the nursery. When preparing
any unlabeled tank mix of pesticides, fertiliz-
ers, and/or spreader stickers, growers should
check the physical and chemical compatibility
of these combinations through a simple jar com-
patibility test. The following steps in perform-
ing the jar test should be followed prior to plant
testing (see previous section).


1. Define the recommended volume or weight
of each material per 100 gal. of water carrier.

2. Calculate the appropriate concentration of
each chemical per pint of water spray volume.

3. Obtain two quart jars and label "with
spreader sticker" and "without spreader

4. Add one pint of water to each jar and the re-
quired amount of spreader sticker to the ap-
propriately labeled jar.

5. Add the desired chemicals for the tank mix
by formulation type and in the calculated
amounts per one pint of water. Add first the
wettable powders (WP), followed by granules
(G), flowables (F), emulsifiable concentrates
(EQ, and finally liquids

6. Close jars and shake vigorously to mix.

7. Observe both jars immediately after agita-
tion and again after 30 minutes.

8. If one or both jars remain suspended (mixed)
or are resuspended easily after 30 minutes (with
minimal agitation), then the tank mix materials
are compatible and can be tested on plants.
Layering of materials in one or both jars indi-
cates physical incompatibility and a more likely
phytotoxic combination. The formation of a
solid precipitate or "gunk" that does not resus-
pend indicates chemical incompatibility and an
unacceptable tank mix combination.

9. Choose the compatible combinations) only
and proceed to evaluate these along the previ-
ously mentioned steps for plant phytotoxicity.

Environmental Factors Influencing

The environment at the time of applica-
tion may play a role in development of plant
injury symptoms. Extremes in temperature can
affect pesticide safety on a plant, thus pesticide
applications should be made between 60 to 850
F. Certain product labels caution against use
when temperatures are 85 F or higher. Ex-
amples of these products include cyclohexim-
ide (Acti-dione), dinocap (Karathane), lime sul-
fur and sulfur fungicides. Other pesticides such
as Bordeaux mixture, dinocap, and fixed cop-
per products can cause plant injury under cool,
dry conditions.

Plant vigor at the time of pesticide ap-
plication can also affect the margin of pesticide
safety. In some cases, stressed plants are more
susceptible to pesticide phytotoxicity than non-
stressed plants. Stresses may be due to a wide

range of causes including extremes of fertilizer,
water, temperature, light and high levels of pest
pressure. Maintaining plants under optimal
conditions will lessen the chances of phytotox-


Avoiding phytotoxicity is not an impos-
sible task and can be accomplished if several
key practices are followed closely.

1. Spray plants only with pesticides known to
be safe for the plant. This can be determined by
reading the label or state publications on rec-
ommended and safe fungicides and through
performance of phytotoxicity trials.

2. Do not tank mix unless the combination of
products is known to be safe. Unlabeled tank
mix combinations should be checked first for
compatibility by the jar test. If mixes are com-
patible, they still must be evaluated on each
plant type (see above).

3. Do not spray stressed plants if this can be

4. Spray plants when temperatures are cool to
warm (below 850F preferably).

5. If the pesticide label instructs that the appli-
cation is to be to the soil then apply it to the
soil. The same holds true for foliar applications.
When certain pesticides are applied to the
wrong portion of a plant, they cause phytotox-
icity which does not occur when applied to the
correct site. Likewise, if the label instructs rins-
ing foliage after application, this must be done
to avoid phytotoxicity.

Figure 1. Deformity of new leaves commonly
occurs on scheffleras treated with one or
more of many pesticides.

Figure 3. Many copper-based products are
used in cooling systems to minimize growth
of fungi and algae in the pads. This
pepperomia leaf shows the speckled necrosis
which occurred when the water from the
pads came in contact with them.

Figure 2. These maranta leaves were acciden-
tally sprayed with a 10% bleach solution
used to disinfest walkways.

Figure 4. Marginal and tip necrosis can
develop when plants are treated with an
excessive amount of a normally safe fungi-

Figure 5. Some copper fungicides are very
toxic to nephthytis; symptoms are generally
marginal chlorosis and necrosis.The leaf on
the left is from an untreated control plant.

Figure 7. Vinclozolin has proved toxic to
zebra plants. Symptoms appear after a single
application of this fungicide and are charac-
teristically confined to severe chlorosis of
new leaves.

Figure 6. Obvious chlorosis occurs when ivy
plants are sprayed with the bactericide
streptomycin sulfate. New leaf tissue appears
white after as little as two applications.

Figure 8. These red marantas show varying
levels of chlorosis caused by a single drench
applicationof benomyl at the recommended
rate. The leaf on the left is from an untreated
control plant.

Figure 9. The white petioles of this parlor
palm developed following incorporation of
ethazole into the potting medium at four
times the recommended rate of use.

Figure 11. Contact burns occur frequently on
foliage plants treated with certain products.
This calathea leaf shows necrosis along the
inner portion of the leaf where fungicide

Figure 10. Application of foliar micronutri-
ents can also cause phytotoxicity such as the
contact burn on this Areca palm which
resulted from an application of Fe 330.

Figure 12. Occasionally a single application
of a pesticide results in complete inhibition
of plant growth. This gloxinia was treated
with a low rate of an experimental com-

Figure 13. The tips of this ivy plant stopped
growing following application of one hun-
dred times the recommended rate of a surfac-

Figure 14. Sometimes the formultion of a
fungicide is responsible for phytotoxicity.
These lipstick vines were treated with a
liquid formulation of iprodione (not com-
mercially available) which resulted in defor-
mity of the new growth. The wettable pow-
der form of this fungicide did not cause
these symptoms. The cutting on the left was
taken from an untreated control plant.

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