PCA WEEDS FINAL EXAM 2026 ACTUAL QUESTIONS AND
SOLUTIONS SCORED 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.
SOLUTIONS SCORED 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.
