Today’s insecticides and fungicides are manufactured from literally hundreds of chemical compounds – both organic and inorganic. These chemical compounds, in turn, can be grouped into several dozen chemical groups. Each group of insecticides and fungicides has associated with it a particular mode of activity or mode of action (MOA). These MOAs serve to describe how a particular chemical or chemical group acts to kill or disable insects or fungi. Table 1 summarizes the six major MOAs and associated chemical groups for insecticides, and Table 2 summarizes the six major MOAs and associated chemical groups for fungicides.
|
MOA |
CHEMICAL
GROUP |
HOW
THEY WORK |
|
1 |
Organophosphates
and Carbamates |
Inhibit
the enzyme acetylcholinesterase which serves to interrupt the
transmission of nerve impulses. |
|
2 |
Chlorinated
Hydro- carbons and Pyrethroids |
Act
as axonic poisons by interfering with the sodium channels of both the
peripheral and central nervous system thereby stimulating repetitive
nervous discharges, leading to paralysis. |
|
3 |
Macrocyclic
Lactone and Carbazates |
Interferes
with the gamma-amino butyric acid (GABA) receptors of insect neurons
leading to repetitive nervous discharges. |
|
4 |
Chloronicotinyls |
Bind
to acetylcholine receptors thereby disrupting nerve impulse
transmission. |
|
5 |
Pyridine,
Triazine, Insect Growth Regulators |
Insect
growth regulators are chitin synthesis inhibitors or juvenile hormone
mimics. Chitin synthesis inhibitors prevent the
formation of chitin, an essential compound in an insect’s exoskeleton.
Juvenile hormone mimics cause insects to remain in an early/young life
stage. |
|
6 |
Soaps
and Oils |
Soaps
and oils work by either damaging the waxy layer of the exoskeleton of
soft-bodied insects, resulting in dessication (drying), or by covering
the breathing pores (spiracles) of insects, resulting in suffocation. |
Here’s
the important point for rosarians: insects and fungi can develop resistance to
insecticides and fungicides if products having the same MOAs are used
repeatedly. The organism targeted for control by a chemical, or chemicals, with
a particular MOA will ultimately mutate and possibly become immune to that
MOA. The solution to this problem is to rotate the
chemicals used among the different MOAs so that, for example, the fungus that is
becoming resistant to MOA-x is now confronted with MOA-y, and so
on. Rotation among the MOAs can be done over time. For
example, spray a product with MOA-x one week and one with MOA-y the
next. For equal effectiveness, products with two different MOAs can
be tank-mixed (if they are otherwise compatible) and applied
together. An example of the latter approach can be found in the
over-the-counter insecticide Bayer Advanced Garden
Rose & Flower Insect Killer manufactured by the Bayer
Company. This product combines Merit (MOA 4) and Tempo (MOA 2) in a
ready to use (RTU) spray.
Table
2. Chemical Group and Fungicide Modes of Action
MOA |
CHEMICAL
GROUP |
HOW
THEY WORK |
|
1 |
Demethylation
Inhibitor (DMI) fungicides such as triazoles and imidazoles, |
Inhibits
the biosynthesis of sterol in fungal membranes. There
are five classes of these sterol biosynthesis inhibitors (SBI)
encompassing 44 different active ingredients – for example,
propiconazole, the active ingredient in Banner MAXX. |
|
2 |
Methyl
Benzimidazole Carbamates – the MBC fungicides such as thiophanates,
benzimidazoles, etc. |
Interferes
with fungal mitosis (normal cell division). There
are four groups of mitosis inhibiting chemicals encompassing nine
different active ingredients – for example, thiophanate-methyl, the
active ingredient in Cleary’s 3336F. |
|
3 |
Dicarboximides
and Carbamates |
Inhibits
membrane synthesis and promotes the oxidation of fungal lipid (“fat”)
molecules. |
|
4 |
Phenylamides
(PA) fungicides |
Inhibits
the synthesis of nucleic acids, both DNA and RNA. There
are three other groups closely related to the PA group, and they and the
PA group encompass 12 different active ingredients. |
|
5 |
Carboxamides
plus Quinone outside Inhibitors (QoI) and Quinone inside Inhibitors (QiI)
fungicides |
Interferes
with fungal respiration. There are seven classes
of respiration inhibitors encompassing 28 different active ingredients
– for example, trifloxystrobin, the active ingredient in the QoI
fungicide, Compass. |
|
6 |
Multi-Site
Contact Activity |
These
fungicides simply act to kill the fungus by overwhelming it with
materials that are poisonous to it. These
fungicides are primarily based on inorganics such as aluminum, copper,
and sulfur, and upon the dithiocarbamates combined with zinc and
manganese ions – this latter group includes the fungicides Manzate,
Maneb, and Junction. Low risk of resistance buildup. |
Now
you know that there are basically six MOAs for insecticides and
fungicides. And you know not to repeatedly use insecticides or
fungicides from the same MOA. However, I recognize that it’s
unlikely you can go to your local garden supply store and say to the
salesperson, “I’d like 6 oz. of a methyl benzimidazole carbamate fungicide,
please” – I don’t think that would work. Therefore, in the next
two tables I’ve identified popular-with-rosarians insecticides
(Table 3) and fungicides (Table 4) by their trade names, and grouped them into
their respective MOAs. Also identified in the tables are the
toxicities of each product, based on the signal word on the labels, i.e., C =
Caution, W = Warning, and D = Danger, and the type of product, i.e., S =
Systemic, T = Translaminar or Locally Systemic, and C =
Contact. Systemic means the product is absorbed by the plant and
moves upward through the plant’s vascular system (but not into the
bloom). Translaminar means the product is absorbed by the plant but
does not move through it. And, contact means the product is active
only on the plant’s surface where it was sprayed.
Based
on my experience with the rotation of fungicides I use a combination of the two
rotation approaches to successfully control (indeed, eliminate) black
spot. For example, I use Banner MAXX, Cleary’s 3336F, and Compass
– each of which has a different MOA. One time I spray with a tank
mix of Banner MAXX and Compass, and the next with a mixture of Cleary’s 3336F
and Compass. This avoids the fungus being exposed to the same MOA for
any length of time.
|
MOA |
CHEMICAL
CLASS |
TRADE
NAME |
TOXICITY |
TYPE |
TYPICAL
APPLICATIONS |
||||
|
C |
W |
D |
S |
T |
C |
||||
|
1 |
Organophosphates |
Orthene |
|
√ |
|
|
√ |
|
Control
of aphids, leafrollers, jap beetles, midge and thrips on roses |
|
Acephate
75 |
√ |
|
|
|
√ |
|
Control
of aphids, thrips and jap beetles on roses |
||
|
Malathion |
√ |
|
|
|
|
√ |
Control
of aphids, jap beetles, leafhoppers, scale, thrips on roses |
||
|
DuraGuard
ME |
√ |
|
|
|
|
√ |
Control
of aphids and thrips on roses |
||
|
Cygon |
|
√ |
|
√ |
|
|
Control
of aphids, leafhoppers and thrips on roses |
||
|
Carbamates |
Mesurol
75-W |
|
|
√ |
|
|
√ |
Control
of aphids and thrips on ornamental plants |
|
|
Sevin |
√ |
|
|
|
|
√ |
Control
of aphids, jap beetles, leafrollers, scale, etc. on roses |
||
|
2 |
Pyrethroids |
Talstar |
√ |
|
|
|
|
√ |
Control
of aphids, jap beetles, thrips, spider mites, etc. on roses |
|
Tempo* |
√ |
|
|
|
|
√ |
Control
of aphids, budworms, thrips, etc. on roses |
||
|
Mavrik |
√ |
|
|
|
|
√ |
Control
of aphids, thrips and spider mites on roses |
||
|
Scimitar |
√ |
|
|
|
|
√ |
Control
of aphids, budworms, jap beetles,thrips, etc. on roses |
||
|
Astro |
√ |
|
|
|
|
√ |
Control
of aphids, jap beetles, whiteflies, etc. on roses |
||
|
Chlorinated Hydrocarbons |
Kelthane |
|
|
√ |
|
|
√ |
Control
of spider mites on roses |
|
|
Thiodan |
|
√ |
|
|
|
√ |
Control
of pests on field crops (eg., corn, tomatoes, etc.) |
||
|
Lindane |
√ |
|
|
|
|
√ |
Seed
and seedling protection of field crops (eg., wheat, barley, etc.) |
||
|
3 |
Glycoside |
Avid |
|
√ |
|
|
√ |
|
Control
of spider mite adults and leafminers on roses |
|
Carbazate |
Floramite |
√ |
|
|
|
|
√ |
Control
of spider mites, at all life stages, on roses |
|
|
Phenoxypyrazole |
Akari
5SC |
|
√ |
|
|
|
√ |
Control
of spider mites, at all life stages, on roses |
|
|
4 |
Chloronicotinyls |
|
√ |
|
|
√ |
|
|
Control
of jap beetles, and thrips on roses |
|
Merit* |
√ |
|
|
√ |
|
|
Control
of aphids, jap beetles, thrips, etc. on roses |
||
|
Spinosin |
Conserve |
√ |
|
|
|
√ |
|
Control
of thrips and spider mites on roses |
|
|
5 |
Growth
Regulators/ Inhibitors |
Azatin |
√ |
|
|
|
|
√ |
Control
of caterpillars, jap beetles and leafrollers on roses |
|
Hexygon |
√ |
|
|
|
|
√ |
Control
of spider mite eggs and larva on roses |
||
|
TetraSan |
√ |
|
|
|
√ |
|
Control
of spider mite eggs and larva on roses |
||
|
6 |
Tetronic
Acid Derivatives Soaps
and Oils |
Forbid
4F |
√ |
|
|
|
√ |
|
Control
of spider mites, at all life stages, on roses |
|
Kontos |
√ |
|
|
√ |
|
|
“Two-way”
systemic for controlling insects |
||
|
Safer’s
Soap |
|
√ |
|
|
|
√ |
Control
of aphids, leafhoppers, spider mites and thrips on roses |
||
*Merit
and Tempo are combined in a single product: Bayer Advanced Garden Rose &
Flower Insect Killer
Modes
of Action (MOA)
1. Inhibits
cholinesterase which, in turn, prevents termination of nerve impulse
transmission
2. Destabilizes
nerve cell membranes
3. Inhibits nerve impulse transmission in chloride ion channels and mitochondrial electron transport thereby causing paralysis.
4. Overstimulates
and blocks postsynaptic nicotine acetylcholine receptors
5. Prevents
formation of insect exoskeleton or causes insect to remain in a young life stage
6. Causes
dessication (drying) or suffocation of insect
Toxicity:
C=Caution, W=Warning, D=Danger
Type:
S=Systemic, T=Translaminar (Locally Systemic), C=Contact
Effective rotation of insecticides
requires moving from one MOA to another. Moving from one chemical class, or
trade name within a single MOA will not prevent the
buildup of insect resistance to insecticides.
|
MOA |
CHEMICAL
GROUP |
TRADE
NAME |
TOXICITY |
TYPE |
TYPICAL
APPLICATIONS FOR THE CONTROL OF |
||||
|
C |
W |
D |
S |
T |
C |
||||
|
1 |
Dimethylation
Inhibitors (DMI) |
Banner
MAXX |
|
√ |
|
√ |
|
|
Blackspot,
powdery mildew, and rust on roses |
|
Bayleton |
√ |
|
|
√ |
|
|
Powdery
mildew on roses |
||
|
Rubigan |
√ |
|
|
|
√ |
|
Powdery
mildew on roses |
||
|
Eagle |
|
|
|
|
|
|
Blackspot,
powdery mildew, and rust on roses |
||
|
Funginex* |
|
|
√ |
√ |
√ |
|
Blackspot,
powdery mildew, and rust on roses |
||
|
Immunox |
|
√ |
|
√ |
|
|
Blackspot
and powdery mildew on roses |
||
|
Fertilome
Liquid |
|
√ |
|
√ |
|
|
Blackspot,
powdery mildew, and rust on roses |
||
|
Systhane |
|
√ |
|
√ |
|
|
Blackspot,
powdery mildew, and rust on roses |
||
| Decree 50WDG | √ |
√ |
Botrytis on roses | ||||||
|
2 |
Methyl
Benzimi- dazole
Carbamates |
Cleary’s
3336 |
√ |
|
|
√ |
|
|
Blackspot
and powdery mildew on roses |
|
Fungo |
√ |
|
|
√ |
|
|
Blackspot
and botrytis on roses |
||
|
3 |
Dicarboximides |
Chipco
26019 |
√ |
|
|
|
|
√ |
Botrytis on roses |
|
4 |
Phenylamides |
Subdue
Maxx |
√ |
|
|
√ |
|
|
Root
and stem rot when applied as drench or surface spray |
|
5 |
Quinone
outside Inhibitors (QoI) |
Compass |
√ |
|
|
|
√ |
|
Blackspot,
powdery and downy mildews, botrytis and rust on roses |
|
Heritage |
√ |
|
|
|
√ |
|
Downy
and powdery mildew, rust and leaf spot on roses |
||
|
6 |
Inorganics (Metals) |
Aliette |
√ |
|
|
√ |
|
|
Downy
mildew on roses |
|
Phyton
27 |
|
|
√ |
|
|
√ |
Backspot,
powdery and downy mildews and botrytis on roses |
||
|
Dithiocarbamates |
Fore |
√ |
|
|
|
|
√ |
Blackspot,
leaf spot and rust on roses |
|
|
Manzate |
√ |
|
|
|
|
√ |
Blackspot
and botrytis on roses |
||
|
Maneb |
√ |
|
|
|
|
√ |
Blackspot,
leafspot and rust on roses |
||
|
Daconil |
|
|
√ |
|
|
√ |
Blackspot
and botrytis on roses |
||
*Now
called Rose & Shrub Disease Control
Modes
of Action (MOA)
1. Inhibits
sterol biosynthesis in membranes
2. Inhibits
mitosis and cell division
3. Inhibits
the production of lipids and membrane synthesis
4. Inhibits
nucleic acid synthesis
5. Inhibits
respiration
6. Multi-mode/multi-site
activity – inherently low (or no) risk for buildup of resistance
Toxicity:
C=Caution, W=Warning, D=Danger
Type:
S=Systemic, T=Translaminar (Locally Systemic), C=Contact
Effective
rotation of fungicides requires moving from one MOA to another. Moving from one
chemical group, or trade name within a single MOA will not prevent the fungus’
buildup of resistance to fungicides.