PCA WEEDS LATEST 2026 EXAM QUESTIONS AND
SOLUTIONS SCORED A+
✔✔Describe cultivation techniques used in perennial crops. - ✔✔Mechanical cultivation
used for seedbed preparation and then hand cultivation used in rows after perennial
crop growth.
✔✔Compare the advantages and disadvantages of different cultivation methods. -
✔✔Hand cultivation: can be closer to the crop but expensive to pay for labor and room
for human error
Mechanical cultivation: inexpensive, but time consuming and often needs a crew to
hand cultivate behind the equipment
✔✔Identify the proper timing for cultivation and hand weeding. - ✔✔When weeds have
just emerged
✔✔Describe the use of the following methods for weed control: burning and flaming -
✔✔Flaming is used to over heat weeds instead of burning, but it is used to burn the
outer layer and allow for dessication
✔✔Describe the use of the following methods for weed control: steaming and
solarization - ✔✔Use of moisture and heat with tarp to over heat weeds and kill them
✔✔Describe how control measures using heat affect weed and crop growth. - ✔✔If not
directed carefully, heat can also damage crop growth. Heat will disrupt epidermal cells
of the plant to induce moisture loss and effectively dry out the plant.
✔✔Describe some preventative measures that can be used to manage weeds (certified
seed, quarantines, clean equipment) - ✔✔Certified seed helps prevent introduction of
weeds such as dodder that have seed that look identical to crop seed. Quarantines help
prevent spread of weeds by setting seed aside or crops aside to eliminate weeds. Clean
equipment helps prevent movement of seed to different fields or spots within a field.
✔✔List the various methods used to classify herbicides. - ✔✔Usage, contact or
systemic, method of translocation, method of application, selectivity, time of application,
plant symptomology, toxicology, chemistry
✔✔Define mode of action and the results of using an herbicide with a given mode of
action - ✔✔Mode of action is the way in which an herbicide controls a weed. For
example, any herbicide that disrupts cell membranes will have similar plant symptoms.
✔✔Amides (propanil) - ✔✔Photosynthesis inhibitors
,✔✔Bipryidiliums (paraquat, diquat) - ✔✔Electron acceptors - PSI (accepts electrons to
form toxic free radicals)
✔✔Dinitroanilines (trifluralin, pendimethalin) - ✔✔MoA- inhibition of cell mitosis
✔✔Diphenylethers (oxyfluorfen) - ✔✔Free radical generators; destruction of cell
membranes
✔✔Glycine (glyphosate) - ✔✔EPSP Synthase Inhibitors, interferes with normal
carbohydrate translocation in plants
✔✔Phenoxy carboxylic acids (auxinic herbicides, 2,4-D) - ✔✔Growth regulators,
regulate plant cell growth and differentiation
✔✔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. Inhibits ALS/AhAS which is the first step in the synthesis of the branched-
chain amino acids valine, leucine and isoleucine
✔✔Thiocarbamates (EPTC, thiobencarb) - ✔✔Energy production inhibitors. Inhibits lipid
synthesis and cell division.
✔✔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.
✔✔Preemergence herbicide - ✔✔A chemical applied to control weeds before their
emergence from the soil.
✔✔Preplant incorporated herbicide - ✔✔Herbicides incorporated by tillage into the soil.
Usually herbicides with low solubility, sensitivity to photodecomposition, and/or high
volatility
✔✔Postemergence herbicide - ✔✔Herbicide applied to foliage of a weed after it
emerges.
, ✔✔Adjuvant - ✔✔Any substance in a formulation to improve herbicidal activity or
application characteristics
✔✔Herbicide resistance - ✔✔Development through natural selection of resistance to
herbicides with specific modes of action
✔✔Cross-resistance - ✔✔Phenomenon in which an individual plant is resistant to two
different herbicides by the same mechanism of resistance
✔✔Multiple resistance - ✔✔Resistance from simultaneous or sequential use of different
herbicides, such that resistance to each herbicide is endowed by a different mechanism
✔✔Soil persistence - ✔✔Refers to the length of time that a herbicide applied to or in soil
remains effective.
✔✔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.
✔✔Describe factors that can cause herbicide injury symptoms on a crop. - ✔✔Species
of plants react differently to an herbicide, environmental differences cause response
differences, plant growth stages will give different symptoms, plant stress alters plant
response
✔✔Describe foliar versus soil application methods for herbicides. - ✔✔Soil: Power
incorporation, disc incorporation, sprinklers, ground-driven rolling cultivators, irrigation
equipment
Foliar: spray tanks, hand sprayers, etc
✔✔Describe how incorporation depth affects preemergence and preplant soil
incorporated herbicide activity. - ✔✔Most preemergent and preplant herbicides need to
be at a depth that water can reach the herbicide so that it can be activated but not too
shallow that they can volatilize
✔✔Describe how herbicide rate affects preemergence and preplant soil incorporated
herbicide activity. - ✔✔Herbicide rate can be damaging to specific crops and needs to
be adjusted so that the rate controls weeds long enough until crop planting but not to
damage the crop
✔✔Describe how soil type and amount of organic matter affects preemergence and
preplant soil incorporated herbicide activity. - ✔✔Soils with a large amount of organic
matter and microorganisms can cause herbicides to become inactivated. Lighter soils
SOLUTIONS SCORED A+
✔✔Describe cultivation techniques used in perennial crops. - ✔✔Mechanical cultivation
used for seedbed preparation and then hand cultivation used in rows after perennial
crop growth.
✔✔Compare the advantages and disadvantages of different cultivation methods. -
✔✔Hand cultivation: can be closer to the crop but expensive to pay for labor and room
for human error
Mechanical cultivation: inexpensive, but time consuming and often needs a crew to
hand cultivate behind the equipment
✔✔Identify the proper timing for cultivation and hand weeding. - ✔✔When weeds have
just emerged
✔✔Describe the use of the following methods for weed control: burning and flaming -
✔✔Flaming is used to over heat weeds instead of burning, but it is used to burn the
outer layer and allow for dessication
✔✔Describe the use of the following methods for weed control: steaming and
solarization - ✔✔Use of moisture and heat with tarp to over heat weeds and kill them
✔✔Describe how control measures using heat affect weed and crop growth. - ✔✔If not
directed carefully, heat can also damage crop growth. Heat will disrupt epidermal cells
of the plant to induce moisture loss and effectively dry out the plant.
✔✔Describe some preventative measures that can be used to manage weeds (certified
seed, quarantines, clean equipment) - ✔✔Certified seed helps prevent introduction of
weeds such as dodder that have seed that look identical to crop seed. Quarantines help
prevent spread of weeds by setting seed aside or crops aside to eliminate weeds. Clean
equipment helps prevent movement of seed to different fields or spots within a field.
✔✔List the various methods used to classify herbicides. - ✔✔Usage, contact or
systemic, method of translocation, method of application, selectivity, time of application,
plant symptomology, toxicology, chemistry
✔✔Define mode of action and the results of using an herbicide with a given mode of
action - ✔✔Mode of action is the way in which an herbicide controls a weed. For
example, any herbicide that disrupts cell membranes will have similar plant symptoms.
✔✔Amides (propanil) - ✔✔Photosynthesis inhibitors
,✔✔Bipryidiliums (paraquat, diquat) - ✔✔Electron acceptors - PSI (accepts electrons to
form toxic free radicals)
✔✔Dinitroanilines (trifluralin, pendimethalin) - ✔✔MoA- inhibition of cell mitosis
✔✔Diphenylethers (oxyfluorfen) - ✔✔Free radical generators; destruction of cell
membranes
✔✔Glycine (glyphosate) - ✔✔EPSP Synthase Inhibitors, interferes with normal
carbohydrate translocation in plants
✔✔Phenoxy carboxylic acids (auxinic herbicides, 2,4-D) - ✔✔Growth regulators,
regulate plant cell growth and differentiation
✔✔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. Inhibits ALS/AhAS which is the first step in the synthesis of the branched-
chain amino acids valine, leucine and isoleucine
✔✔Thiocarbamates (EPTC, thiobencarb) - ✔✔Energy production inhibitors. Inhibits lipid
synthesis and cell division.
✔✔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.
✔✔Preemergence herbicide - ✔✔A chemical applied to control weeds before their
emergence from the soil.
✔✔Preplant incorporated herbicide - ✔✔Herbicides incorporated by tillage into the soil.
Usually herbicides with low solubility, sensitivity to photodecomposition, and/or high
volatility
✔✔Postemergence herbicide - ✔✔Herbicide applied to foliage of a weed after it
emerges.
, ✔✔Adjuvant - ✔✔Any substance in a formulation to improve herbicidal activity or
application characteristics
✔✔Herbicide resistance - ✔✔Development through natural selection of resistance to
herbicides with specific modes of action
✔✔Cross-resistance - ✔✔Phenomenon in which an individual plant is resistant to two
different herbicides by the same mechanism of resistance
✔✔Multiple resistance - ✔✔Resistance from simultaneous or sequential use of different
herbicides, such that resistance to each herbicide is endowed by a different mechanism
✔✔Soil persistence - ✔✔Refers to the length of time that a herbicide applied to or in soil
remains effective.
✔✔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.
✔✔Describe factors that can cause herbicide injury symptoms on a crop. - ✔✔Species
of plants react differently to an herbicide, environmental differences cause response
differences, plant growth stages will give different symptoms, plant stress alters plant
response
✔✔Describe foliar versus soil application methods for herbicides. - ✔✔Soil: Power
incorporation, disc incorporation, sprinklers, ground-driven rolling cultivators, irrigation
equipment
Foliar: spray tanks, hand sprayers, etc
✔✔Describe how incorporation depth affects preemergence and preplant soil
incorporated herbicide activity. - ✔✔Most preemergent and preplant herbicides need to
be at a depth that water can reach the herbicide so that it can be activated but not too
shallow that they can volatilize
✔✔Describe how herbicide rate affects preemergence and preplant soil incorporated
herbicide activity. - ✔✔Herbicide rate can be damaging to specific crops and needs to
be adjusted so that the rate controls weeds long enough until crop planting but not to
damage the crop
✔✔Describe how soil type and amount of organic matter affects preemergence and
preplant soil incorporated herbicide activity. - ✔✔Soils with a large amount of organic
matter and microorganisms can cause herbicides to become inactivated. Lighter soils
