PCA Weeds Exam 2026/2027 COMPLETE
QUESTIONS WITH ANSWERS GRADED A+
Dicot -✓✓ have two seed leaves inside the seed coat. They are usually rounded and fat,
because they contain the endosperm to feed the embryo plant
• Monocot -✓✓ An angiosperm that has only one seed leaf.
• reproductive capability of weeds -✓✓ weeds often form persistent seedbanks and can
reproduce at a young age. rhizomes or other vegetative structures, these plants can
form thick, single-species stands.
• Describe the mechanisms by which weed seeds are disseminated. -✓✓ Wind, water,
animal + human: poop, clothing/fur, accidental planting, transport, soil movement,
• Describe how the following factors contribute to regulating the seed bank and seed
longevity:
Cultural -✓✓ Mulching
• Describe and give an example of biological weed control using:
a. arthropods;
b. pathogens;
c. grazing animals. -✓✓ Arthropods- cochineal attacking prickly pear cactus.
Pathogens- Using rust to control orange wattle
Grazing animals- Goats eating weeds to prevent reseeding and fires.
• Soil solarization -✓✓ Not only kill pathogens, but can cook/destroy weed seeds to a
certain depth.
• Weed control: steaming -✓✓ The use of high temperature water onto weeds
• Describe some preventative measures that can be used to manage weeds:
Quarantine -✓✓ Hold livestock that may be infested with seed in a single location until
they are shorn or until weed seeds have had the chance to pass through their digestive
system.
Feed out infested fodder in a feed lot type situation only and introduce clean fodder to
stock.
• Mode of Action -✓✓ The mechanisms by which herbicides kill plants
• amides (propanil) -✓✓ MoA- inhibition of their photosynthesis and CO2 fixation
• bipyridiliums (paraquat, diquat) -✓✓ MoA- inhibiting photosynthesis
, • dinitroanilines (trifluralin, pendimethalin); -✓✓ MoA- inhibition of cell mitosis
• diphenylethers (oxyfluorfen); -✓✓ MoA- upturing of the cell membrane. Soil and foliar
applied with limited movement in the soil
• glycine (glyphosate); -✓✓ MoA- binds to and blocks the activity of the enzyme
enolpyruvylshikimate-3-phosphate synthase
• phenoxy carboxylic acids (auxinic herbicides, 2,4-D); -✓✓ MoA- plant growth hormone
auxin, which results in uncontrolled growth and eventually death. selective herbicide
which kills many terrestrial and aquatic broadleaf weeds
• phosphinic acid (glufosinate); -✓✓ MoA- glutamine synthetase inhibitor that binds to
the glutamate site. die due to a buildup of ammonia in the thylakoid lumen
• sulfonylureas (chlorsulfuron, rimsulfuron); -✓✓ MoA- direct inhibition of DNA synthesis.
• thiocarbamates (EPTC, thiobencarb); -✓✓ MoA-
• triazines (atrazine, simazine); -✓✓ MoA- act as inhibitors of plastoquinone binding;
inhibits Photosystem II
• ureas (linuron, diuron). -✓✓ MoA- foliar absorbed and residual herbicide. inhibits
photosynthesis at photosystem II
• phytotoxicity; -✓✓ Injury or damage to a sensitive plant caused by a chemical
exposure.
• adjuvant; -✓✓ ormulation or added to the spray tank to improve herbicidal activity or
application characteristics.
• cross-resistance; -✓✓ Refers to a biotype that is resistant to two or more chemically
similar herbicides
• multiple resistance; -✓✓ Refers to weed biotype that is resistant to two or more
chemically unrelated herbicides
• plantback restrictions. -✓✓ some pesticides can adversely affect the growth of
sensitive rotational crops or because a tolerance for the active ingredient has not been
established for the next crop in rotation.
QUESTIONS WITH ANSWERS GRADED A+
Dicot -✓✓ have two seed leaves inside the seed coat. They are usually rounded and fat,
because they contain the endosperm to feed the embryo plant
• Monocot -✓✓ An angiosperm that has only one seed leaf.
• reproductive capability of weeds -✓✓ weeds often form persistent seedbanks and can
reproduce at a young age. rhizomes or other vegetative structures, these plants can
form thick, single-species stands.
• Describe the mechanisms by which weed seeds are disseminated. -✓✓ Wind, water,
animal + human: poop, clothing/fur, accidental planting, transport, soil movement,
• Describe how the following factors contribute to regulating the seed bank and seed
longevity:
Cultural -✓✓ Mulching
• Describe and give an example of biological weed control using:
a. arthropods;
b. pathogens;
c. grazing animals. -✓✓ Arthropods- cochineal attacking prickly pear cactus.
Pathogens- Using rust to control orange wattle
Grazing animals- Goats eating weeds to prevent reseeding and fires.
• Soil solarization -✓✓ Not only kill pathogens, but can cook/destroy weed seeds to a
certain depth.
• Weed control: steaming -✓✓ The use of high temperature water onto weeds
• Describe some preventative measures that can be used to manage weeds:
Quarantine -✓✓ Hold livestock that may be infested with seed in a single location until
they are shorn or until weed seeds have had the chance to pass through their digestive
system.
Feed out infested fodder in a feed lot type situation only and introduce clean fodder to
stock.
• Mode of Action -✓✓ The mechanisms by which herbicides kill plants
• amides (propanil) -✓✓ MoA- inhibition of their photosynthesis and CO2 fixation
• bipyridiliums (paraquat, diquat) -✓✓ MoA- inhibiting photosynthesis
, • dinitroanilines (trifluralin, pendimethalin); -✓✓ MoA- inhibition of cell mitosis
• diphenylethers (oxyfluorfen); -✓✓ MoA- upturing of the cell membrane. Soil and foliar
applied with limited movement in the soil
• glycine (glyphosate); -✓✓ MoA- binds to and blocks the activity of the enzyme
enolpyruvylshikimate-3-phosphate synthase
• phenoxy carboxylic acids (auxinic herbicides, 2,4-D); -✓✓ MoA- plant growth hormone
auxin, which results in uncontrolled growth and eventually death. selective herbicide
which kills many terrestrial and aquatic broadleaf weeds
• phosphinic acid (glufosinate); -✓✓ MoA- glutamine synthetase inhibitor that binds to
the glutamate site. die due to a buildup of ammonia in the thylakoid lumen
• sulfonylureas (chlorsulfuron, rimsulfuron); -✓✓ MoA- direct inhibition of DNA synthesis.
• thiocarbamates (EPTC, thiobencarb); -✓✓ MoA-
• triazines (atrazine, simazine); -✓✓ MoA- act as inhibitors of plastoquinone binding;
inhibits Photosystem II
• ureas (linuron, diuron). -✓✓ MoA- foliar absorbed and residual herbicide. inhibits
photosynthesis at photosystem II
• phytotoxicity; -✓✓ Injury or damage to a sensitive plant caused by a chemical
exposure.
• adjuvant; -✓✓ ormulation or added to the spray tank to improve herbicidal activity or
application characteristics.
• cross-resistance; -✓✓ Refers to a biotype that is resistant to two or more chemically
similar herbicides
• multiple resistance; -✓✓ Refers to weed biotype that is resistant to two or more
chemically unrelated herbicides
• plantback restrictions. -✓✓ some pesticides can adversely affect the growth of
sensitive rotational crops or because a tolerance for the active ingredient has not been
established for the next crop in rotation.
