Pesticides are designed to kill or alter the
behavior of pests.
When, where, and how they can be used safely
and effectively is a matter of considerable
public interest.
If they are not used wisely, pesticides may
pose risks to pesticide applicators and other
exposed people, and may create long-term environmental
problems.
I’m Dr. DeBusk and I’m going to talk about
pesticides and what affects them.
A pest-control strategy should be used only
when the pest is causing or is expected to
cause more damage than what can be reasonably
and economically tolerated.
A control strategy should be implemented that
reduces the pest numbers to an acceptable
level while minimizing harm to nontargeted
organisms.
The strategy of IPM is as follows: Prevention
- keeping a pest from becoming a problem,
and then, if needed, Suppression - reducing
pest numbers or damage to an acceptable level.
Always follow the directions on the label.
These directions have been developed after
extensive research and field studies on the
chemistry, biological effects, and environmental
fate of the pesticide.
The label is the single most important document
in the use of a pesticide.
State and federal pesticide laws require following
label directions!
The following general BMPs should always be
used for pesticides: Develop and implement
a quality IPM program.
Observe all directions, restrictions, and
precautions on pesticide labels.
It is dangerous, wasteful, and illegal to
do otherwise.
Store pesticides behind locked doors in original
containers with labels intact, separate from
seed and fertilizer.
Use pesticides at the correct application
rate and recommended intervals between applications
to avoid injury to plants and animals.
Never eat, drink, or smoke when handling pesticides,
and always wash with soap and water after
use.
Triple-rinse containers into the spray tank.
Never pour pesticides down a drain or into
an area exposed to humans, animals, or water.
Dispose of used containers in compliance with
label directions so that water contamination
and other hazards will not result.
Always wear protective clothing when applying
pesticides.
At a minimum, wear a longsleeved shirt, long-legged
pants, rubber gloves, boots (never go barefoot
or wear sandals), eye protection, and a wide-brimmed
hat.
Additional protective gear may be listed on
the pesticide label.
Identifying or recognizing pests is essential
to proper pesticide application and selection.
Once the pest has been identified, the best
control method must be chosen.
If a pesticide is to be used, the applicator
must know the proper application technique
and read the label thoroughly.
Pesticides should be evaluated on effectiveness
against the pest, mode of action, life stage
of the pest, personnel hazards, non-target
effects, leaching or runoff potential, and
cost.
Pesticide selection BMPs include: Develop
and implement a quality IPM program.
Train employees in proper pest identification
and pesticide selection techniques.
Choose the product most appropriate for the
problem or pest.
Mix only the quantity of pesticide needed
in order to avoid disposal problems, protect
non-targeted organisms, and save money.
Spot-treat pests whenever appropriate.
Read and follow all label directions.
The label is a legal document.
Make note of any groundwater advisories on
the label.
Have you ever wondered how pesticides control
an insect, pathogen or weed?
The manner in which a pesticide destroys or
controls a pest is called its “mode of action.”
A similar term, but with a more specific meaning,
is “mechanism of action.”
This term is used to describe the exact location
of inhibition, such as interfering with the
activity of an enzyme within a metabolic pathway.
It is easier to choose the right pesticide
if you understand how it works.
Then you can make an informed decision about
which pesticide will be most effective in
a particular situation.
There are many other classes of pesticides;
however, the major classes of pesticides that
are handled by lawn and ornamental managers
are insecticides, fungicides, and herbicides.
Insecticides are toxins that kill insects;
they have many different modes of action.
General insecticide modes of action include:
Block signals to the insect’s nerves or
muscles; Desiccate the insect; Change normal
growth; Prevent insect reproduction; Suffocate
the insect; and Destroy the insect’s digestive
tract (Bt).
Insecticides can prevent damage if applied
when insects lay eggs or the eggs hatch.
These are preventive insecticides used in
areas that have had previous insect infestations.
Insecticides applied after damage appears
are curative - they control insects that caused
the damage.
Herbicides are pesticides that specifically
control weeds.
The mode of action of an herbicide often governs
when and how you use it.
Some herbicides prevent seed germination or
seedling growth shortly after germination
- these are called “preemergence herbicides.”
These herbicides must be applied to the soil
to control weed seedlings before they emerge.
Apply postemergence herbicides to the leaves
and stems or soil surrounding actively growing
weeds.
Some postemergence herbicides kill weeds by
contact activity, affecting only those parts
of the weed touched by the herbicide.
Other postemergence herbicides translocate
within the tissues of the plant from leaves
and other green parts to the growing points.
These herbicides are also referred to as systemic.
General herbicide modes of action include:
Inhibition of photosynthesis; Inhibition of
amino acids and protein development; Inhibition
of fatty acid synthesis; Inhibition of growth;
Inhibition of cell membrane development; Inhibition
of pigment synthesis; and Growth regulation.
A fungicide is a specific type of pesticide
that controls fungal disease by specifically
inhibiting or killing the fungus causing the
disease.
Not all diseases caused by fungi can be adequately
controlled by fungicides.
To be effective, most fungicides need to be
applied before disease occurs or at the first
appearance of symptoms.
Fungicides can only protect new uninfected
growth from disease, thus are called “protectants.”
Also, few fungicides are effective against
pathogens after they have infected a plant--
these are called “eradicants” or “curatives.”
General fungicide modes of action include:
Inhibition of nucleic acids synthesis; Inhibition
of mitosis and cell division; Inhibition of
respiration; Inhibition of amino acids and
protein development; Inhibition of signal
transduction; Inhibition of cell membrane
development; Inhibition of sterol biosynthesis;
Inhibition of cell wall biosynthesis; Host
plant defense induction; and Multi-site activity.
Several factors influence how a pest reacts
to a pesticide.
Two of these are very important: 1) The life
stage of the pest or target organism and 2)
Pesticide uptake.
Insecticides usually are most effective on
nymphs or larvae, and in some situations,
adults.
Eggs and pupae are often located in protected
areas.
These life stages do not feed so they do not
cause damage.
Herbicides generally are more effective on
young, actively growing plants than on mature
weeds.
Some herbicides will control perennial plants
when they are applied just prior to flowering.
The same herbicides are not as effective when
applied to plants that have not begun to flower
or have completed flowering.
Perennial weeds are difficult to control once
their rhizomes and other vegetative reproductive
structures are well-developed.
Most pesticides have certain sites of action
within the pest where their toxic effects
are imparted.
Before the pesticide can exert its effect,
it must enter and translocate into the pest’s
tissues to these sites; this is called “pesticide
uptake.”
Factors that influence pesticide uptake include:
Structure of the pest, outer tissue or cuticle
on the plant or insect that protects it, habits
of pest, formulation of the pesticide, and
environmental conditions.
Terms that describe the methods and routes
of pesticide uptake include:
Contact: A pesticide with contact activity
passes through the pest’s cuticle.
Stomach poison: The pest must consume the
active ingredient in the pesticide.
The toxin is absorbed into the lining of the
pest’s mouthparts or intestine.
Fumigant: The pesticide passes as a vapor
or gas into the pest’s tissues.
The pest inhales the pesticide or it passes
through the pest’s skin or cuticle.
Some pesticides enter pests by all of these
methods.
Pesticides are valuable additions to the box
of tools available to pest managers.
However, they should be considered one part
of the total IPM plan rather than the only
solution.
Pesticide failure can occur for a variety
of reasons: Improper pest identification (incorrect
pesticide selection); Incorrect pesticide;
Dosage; Improper application timing; Pesticide
does not reach target pest; Unfavorable environmental
conditions; State of poor pesticide condition;
and Pesticide resistance.
Accurate pest identification should be the
first step.
Being able to accurately identify pests requires
patience and practice.
Subtle differences among pest species may
often lead to a false identification.
For example, control methods vary for different
species of grassy weeds.
Although they may have common features, such
as parallel veins and round stems, crabgrass
and bermudagrass control tactics are not always
the same.
Crabgrass is an annual, while bermudagrass
is a tougher-to-control perennial with vegetative
rhizomes and stolons.
Although some postemergence herbicides may
control both species, preemergence herbicides
will only reliably control crabgrass.
Likewise, different species of mites can be
difficult to distinguish from one another
because of their extremely small bodies.
However, the pesticides selected to control
different mite species can vary.
It can even be challenging to distinguish
mites from insects that also possess very
small bodies, such as aphids.
Management and pesticide selection can be
very different for controlling mites and insects.
Regardless of the pest class, making an accurate
identification is critical.
UF/IFAS offers a variety of services to help
determine the cause of plant problems and
to provide pest identification through the
UF/IFAS Plant Diagnostic Center.
For more information, go to the web address
shown on the bottom of the screen.
Several reasons may account for this problem.
Application equipment should be properly calibrated
to deliver a known volume.
Underdosing can be expensive because retreatment
may be necessary.
On the other hand, overdosing is a violation
of the product’s label wording, can be phytotoxic,
and harmful to the environment.
Keep in mind that the rate listed on a product
label as controlling one specific pest will
not necessarily be the amount needed to control
other species.
Apply the pesticide to the life stage of the
pest that is most susceptible to the effects
of the pesticide.
Generally, herbicides are most effective on
small, early stages of weed growth.
Many insecticides are effective on insect
larvae or nymphs but not on adults.
Some pesticide labels will list their rates
based upon growth stage or size.
Another potential problem involving timing
is an application that takes place after the
infiltration or departure of a pest.
An application of a protectant fungicide will
provide little or no control of a plant pathogen
that has already invaded its host plant.
Many labels will instruct that applications
should begin prior to the onset of infection.
Sometimes pesticide applications aren’t
effective because the pest is in a location
that is difficult to reach.
Many insects are located on the underside
of leaves, under bark or soil, or within stems
and fruits.
When insects are on leaf undersides, applicator
sprays must be directed at those areas to
have an effect.
After application, some pesticides must be
watered, by either rainfall or irrigation,
into the soil zone where underground insects
are feeding.
Read the label for maximum product efficacy.
Aside from the previous examples, most pesticides
should not be applied just before or during
rainfall.
Rain washes pesticides off foliage before
they have time to take effect.
High temperatures, lack of moisture, and both
acid and alkaline soil pH are conducive conditions
for weeds to develop thicker cuticle formation
on their leaf surfaces.
Thick cuticles prevent, or minimize, herbicide
uptake; thus, weed control is not maximized.
Windy conditions can cause pesticides to drift
from their intended sites and can also result
in damage to desirable plants.
Injuries of this sort are subject to legal
penalties.
Under some conditions, some pesticides can
change into a form that is not effective.
The age of the pesticide, moisture, and temperature
extremes are the primary factors responsible
for chemical reactions that alter the formulation’s
active ingredient, rendering them ineffective.
Moisture is generally a problem when dry products
are stored in bags or containers that have
not been adequately sealed.
Statements on the product’s label often
instruct the user not to store the product
in extreme heat.
Heat may also volatilize some pesticides if
their containers are not adequately sealed.
Such statements are found in the “Storage
and Disposal” section of the product labels.
Using mix water that is alkaline (pH > 7)
is known to degrade some pesticides relatively
quickly.
There are water sources in Florida that tend
to be on the alkaline side of the pH scale.
Historically, this has been the case with
carbamate and organophosphate insecticides;
however, it is not strictly limited to those
classes.
Likewise, some pesticides lose their effectiveness
when mixed with water that contains suspended
or dissolved solids.
Product labels will carry statements cautioning
the applicator of such problems.
Labels may also recommend the use of specialty
adjuvants to alleviate such problems.
Resistance to pesticides is a serious, and
growing, problem.
Worldwide, more than 600 species of pests
have developed some level of pesticide resistance.
If resistance to a particular pesticide or
“family” of pesticides evolves, these
products can no longer be effectively used,
thereby reducing the options available for
pest management.
With few new pesticide modes of action in
the development pipeline, landscape managers
must do all they can to extend the useful
life of the products currently available.
Landscape managers in Florida have become
more aware of pesticide resistance development
in key turfgrass and ornamental plant pests.
A biotype of whitefly could cause serious
impacts to Florida consumers because there
are populations that have reduced susceptibility
to a variety of insecticides, including some
of the most widely used chemical classes (neonicotinoids
and insect growth regulators) for whitefly
control.
The leafminer caused significant damage to
annual bedding plants in the 1970s and early
1980s, which resulted in considerable insecticide
use on infested plants, and subsequent resistance
development to several chemical classes.
How does pesticide resistance develop?
Resistance can develop when the same pesticide
or similar ones with the same mode of action
are used over and over again.
It often is thought that pests change or mutate
in response to a pesticide to become resistant.
However, it is not the individual pest that
changes, but the population.
When a pesticide is applied to a site, a tiny
proportion of the pest population; for example,
one insect or weed in 10 million may survive
exposure to the pesticide due to its genetic
makeup.
When the pests that survive breed, some of
their offspring will inherit the genetic trait
that confers resistance to the pesticide.
These pests will not be affected the next
time a similar pesticide is used.
If the same pesticide is applied often, the
proportion of less-susceptible individuals
in the population will increase.
This illustration shows a “normal” (susceptible)
pest population shaded in red.
However, over time, this population becomes
dominant with a resistant population (shaded
in green).
Although the members of the resistant population
appear identical to the members of the susceptible
population, they are genetically distinct.
These individuals are known as a “biotype.”
A biotype is a group of organisms within a
species that has biological traits (such as
resistance to a particular herbicide) not
common to the population as a whole.
A similar term, but with an entirely different
meaning, is tolerance.
The terms are not always clearly distinguished
and often are used as synonyms.
Tolerance is characterized by survival of
the normal population of a pest species following
a pesticide dosage lethal to other species.
With herbicides, for example, broad-leaved
plants are relatively more susceptible than
some grass species to herbicides that contain
the active ingredient 2,4-D.
How can pesticide resistance be managed, or
at least have its development delayed?
Rotate pesticides with different mechanisms
of action, not just different label names.
Avoid consecutive applications of the same
pesticide unless it is used in a tank-mix
or prepack containing a pesticide with a different
mechanism of action, or is used with other
pest management options such as mechanical
and biological methods.
The pesticides and/or alternative methods
used must be active against the target pest.
Use pesticides with different mechanisms of
action in the same spray tank, in a given
season or between seasons.
This can be accomplished most efficiently
with tank-mixes and pre-packs.
Tank-mixes and pre-packs are combinations
of two or more pesticides applied as a single
mixture.
Tank-mixing allows for adjusting of the ratio
of pesticides to fit local conditions, while
premixes are formulated by the manufacturer.
The combinations are designed to broaden the
spectrum of pests controlled by an individual
pesticide and, if the combination is composed
of pesticides with different mechanisms of
action active against the same pests, will
contribute to resistance management.
The different pesticides in the mixture must
be active against the target pests, so that
biotypes resistant to one mechanism of action
are controlled by the pesticide partner with
a different mode of action.
Theoretically, repeated use of any tank-mix
or pre-pack combination may give rise to pesticide
resistance if resistance mechanisms to each
herbicide in the mix arise together, but the
probability is very low.
Knowing the chemical family and mechanism
of action group to which a pesticide belongs
and knowing which other pesticides have the
same mechanism of action are critical for
creating a plan to prevent or delay development
of pesticide resistance.
A pesticide mechanism of action group is composed
of pesticides that have the same mechanism
of action.
The Fungicide, Herbicide, and Insecticide
Resistance Action Committees have developed
a scheme based on the various groups for those
three classes of pesticides.
The classification systems are based on numbers
assigned to each mechanism of action group
to assist managers in rotating pesticides
with different mechanisms of action.
Encouraged by EPA to use the classification
scheme, some manufacturers are using the system
by displaying the group number(s) prominently
on their labels.
If there is no group information listed in
the product label, refer to the tables listed
in the Resistance Action Committees’ websites
to determine the mechanism of action and group
number of the pesticide you are using.
Where feasible, rotate to other pesticides
with different group numbers for future applications
on the same site.
In addition to considering group numbers in
the selection of pesticides, review all resistance
management recommendations printed on the
product label.
This may include information on the best management
practices for a particular product, target
species of most concern, and the maximum number
of consecutive applications that should be
made before rotating to products containing
pesticides with different group numbers.
Always keep in mind that a perceived product
failure or poor pesticide performance does
not always indicate pest resistance.
Poor control may be the result of any of the
factors discussed previously in this section.
Generally, the best approach to resistance
management is IPM with utilizing all available
control methods, including mechanical and
biological controls where feasible along with
proper cultural practices.
In conclusion, you should have learned about
the three classes of pesticides, how pests
react toward pesticides, and reasons why a
pesticide may be ineffective at controlling
the target pest.
