Which three conditions are required for a typical infectious plant disease to develop?
A Excess fertilizer, dry soil, weeds
B Susceptible host, pathogen, favorable environment
C Healthy host, beneficial insect, sunlight
D High yield, poor storage, drought
Answer: B. Susceptible host, pathogen, favorable environment. The disease triangle links a susceptible host, a capable pathogen and an environment favorable for disease development.
How can the disease triangle guide management choices?
A Can interrupt disease development
B Can identify every pathogen
C Can guarantee a disease-free crop
D Can replace field diagnosis
Answer: A. Can interrupt disease development. Management can target the host, pathogen or environment; reducing any required component can limit disease development.
Where do common plant pathogens belong among these groups?
A Fungi, bacteria, viruses, nematodes
B Birds, mammals, reptiles, fish
C Minerals, salts, sugars, starches
D Rain, wind, sunlight, frost
Answer: A. Fungi, bacteria, viruses, nematodes. Important plant pathogens include fungi, bacteria, viruses and plant-parasitic nematodes.
Yellowing on one leaf by itself provides what kind of evidence?
A Confirmed evidence of bacteria
B Proof of fungal infection
C A virus identification
D Possible symptom, not a diagnosis
Answer: D. Possible symptom, not a diagnosis. Yellowing is a symptom that can result from disease or noninfectious stress, so it does not identify a cause by itself.
What distinguishes a pathogen sign from a plant symptom?
A Any change in plant growth
B A soil nutrient measurement
C A field’s weather history
D Visible pathogen or its structures
Answer: D. Visible pathogen or its structures. A sign is direct evidence of the pathogen, such as mycelium or spores; a symptom is the plant’s response.
Which observation is a plant disease symptom?
A Fungal spores on tissue
B Bacterial ooze from a lesion
C Leaf chlorosis
D Visible nematode cysts
Answer: C. Leaf chlorosis. Chlorosis is yellowing of plant tissue and describes a host response rather than the pathogen itself.
Mycelial growth visible on an infected leaf is best classified as what?
A A pathogen sign
B A nutrient deficiency
C A plant symptom
D An irrigation record
Answer: A. A pathogen sign. Visible fungal growth is part of the pathogen and is therefore a sign of disease.
Why should a grower seek a reliable diagnosis before choosing a fungicide?
A Increase the spray volume
B Rule out nonfungal causes
C Avoid checking the crop
D Treat every leaf symptom
Answer: B. Rule out nonfungal causes. Fungicides do not address abiotic disorders or every pathogen, so diagnosis helps avoid ineffective or unnecessary treatment.
What does inoculum mean in plant pathology?
A Plant tissue damaged by wind
B Pathogen material causing infection
C Nutrients available to roots
D Water stored in leaves
Answer: B. Pathogen material causing infection. Inoculum is pathogen material capable of initiating infection, such as spores, infected seed or contaminated plant debris.
Primary inoculum is important because it does what?
A Measures final crop yield
B Starts infection during season
C Improves host resistance
D Eliminates secondary spread
Answer: B. Starts infection during season. Primary inoculum initiates the first infections in a crop or growing period.
After initial infections form, secondary inoculum mainly does what?
A Prevents pathogen reproduction
B Spreads from earlier infections
C Changes soil texture
D Makes plants immune
Answer: B. Spreads from earlier infections. Secondary inoculum produced by initial infections can spread and cause further infections during the season.
In an infectious disease cycle, infection refers most closely to which event?
A Visible symptoms at harvest
B Successful entry and establishment
C Spore release into air
D A crop’s first irrigation
Answer: B. Successful entry and establishment. Infection involves a pathogen entering and establishing in host tissue; visible symptoms may appear later or not at all.
What typically follows pathogen reproduction in many disease cycles?
A Host plant flowering
B Soil nutrient depletion
C Crop seed certification
D Dispersal to new hosts
Answer: D. Dispersal to new hosts. New spores or other propagules can disperse from infected tissue to susceptible hosts and initiate further infections.
For many pathogens, what does the latent period measure?
A Time from planting to flowering
B Time between harvests
C Time needed for diagnosis
D Time from infection to sporulation
Answer: D. Time from infection to sporulation. The latent period is commonly measured from infection until the pathogen produces new inoculum, such as spores.
Polycyclic diseases are characterized by which pattern?
A Several cycles within one season
B One infection for all years
C No secondary infections
D Only seed transmission
Answer: A. Several cycles within one season. Polycyclic pathogens can produce repeated infection cycles within a growing season, often accelerating epidemics.
Which pattern best describes a monocyclic disease during a growing season?
A Daily cycles of new spores
B Repeated cycles every week
C No primary inoculum
D One main cycle per season
Answer: D. One main cycle per season. Monocyclic diseases generally have one main infection cycle in a season, although their inoculum may survive between seasons.
Why do leaf wetness and humidity matter for many plant diseases?
A Prevent pathogen survival
B Support spore germination
C Guarantee host resistance
D Stop infection pathways
Answer: B. Support spore germination. Many fungal and oomycete pathogens need suitable moisture or leaf wetness for spore germination and infection.
For diseases spread by water splash, what risk can overhead irrigation raise?
A Leaf wetness and splash spread
B Seed purity and germination
C Root depth and flowering
D Resistance in every cultivar
Answer: A. Leaf wetness and splash spread. Overhead irrigation can extend leaf wetness and splash propagules for some diseases; risk depends on crop and pathogen.
When foliar disease is a concern, drip irrigation may help by doing what?
A Sterilize the soil
B Remove infected seed
C Keep foliage drier
D Cure established infections
Answer: C. Keep foliage drier. Drip irrigation directs water toward the root zone and can avoid wetting foliage, though it does not eliminate all disease risk.
How can suitable plant spacing reduce disease-conducive conditions?
A Increase leaf-to-leaf contact
B Improve airflow, reduce humidity
C Raise soil salinity
D Spread infected seed
Answer: B. Improve airflow, reduce humidity. Spacing that improves airflow can help foliage dry faster and reduce prolonged humid conditions in some crops.
When does crop rotation best suppress a soilborne pathogen?
A The same host returns yearly
B The pathogen infects every crop
C Residues remain heavily infected
D Use a nonhost rotation crop
Answer: D. Use a nonhost rotation crop. Rotation can reduce some host-specific soilborne pathogens when a suitable nonhost crop is used and pathogen survival is limited.
Planting tested, healthy seed helps manage disease by doing what?
A Limit seedborne pathogen introduction
B Eliminate all soil pathogens
C Increase leaf wetness
D Replace crop scouting
Answer: A. Limit seedborne pathogen introduction. Healthy seed reduces the chance that seedborne pathogens will be introduced into a crop.
Disease-free nursery stock mainly supports which management goal?
A Reduce pathogen introduction
B Increase crop susceptibility
C Promote infected debris
D Delay field diagnosis
Answer: A. Reduce pathogen introduction. Clean planting stock helps exclude pathogens from new fields or production areas.
Removing infected crop residues can reduce which source of disease?
A Increase host susceptibility
B Create new infection sites
C Raise pathogen virulence
D Lower pathogen inoculum
Answer: D. Lower pathogen inoculum. Infected residues can serve as inoculum for some pathogens, so appropriate sanitation may reduce disease carryover.
Roguing refers to which field practice?
A Remove diseased individual plants
B Apply fertilizer in rows
C Store seed in bags
D Measure leaf wetness
Answer: A. Remove diseased individual plants. Roguing is the removal of infected plants or plant parts to reduce sources of inoculum, where practical.
Seed treatment is used most directly to protect which stages?
A Cure every mature plant
B Remove all field vectors
C Protect seeds and seedlings
D Increase crop flowering
Answer: C. Protect seeds and seedlings. Appropriate seed treatments can reduce seedborne or early soilborne infection risks, but they do not cure every disease.
What should a grower expect from a resistant cultivar?
A Prevent every possible disease
B Reduce damage, not guarantee immunity
C Remove the need for diagnosis
D Kill pathogens in soil
Answer: B. Reduce damage, not guarantee immunity. Resistance can reduce infection or disease severity, but performance depends on the pathogen, cultivar and conditions.
How does a tolerant cultivar differ from a resistant cultivar?
A Prevent all pathogen contact
B Sterilize nearby soil
C Maintain yield despite infection
D Stop pathogen reproduction completely
Answer: C. Maintain yield despite infection. Tolerance generally means a plant sustains less damage or yield loss despite infection, rather than preventing infection.
Plant quarantine and exclusion measures aim to do what?
A Prevent pathogen introduction
B Increase pathogen dispersal
C Promote infected planting stock
D Replace resistant varieties
Answer: A. Prevent pathogen introduction. Exclusion aims to reduce the introduction of pathogens through planting material, equipment or other pathways.
What does a disease forecasting model typically estimate?
A Guarantee crop yield
B Estimate infection risk and timing
C Identify every symptom automatically
D Measure seed purity
Answer: B. Estimate infection risk and timing. Forecasting uses factors such as weather, crop stage and pathogen biology to estimate disease risk and inform timing.
During disease scouting, which observations are especially useful?
A Record only fertilizer costs
B Ignore crop growth stage
C Check only healthy plants
D Find patterns and new symptoms
Answer: D. Find patterns and new symptoms. Regular scouting records symptoms, distribution, crop stage and changes over time to support diagnosis and decisions.
Abiotic plant disorders are caused primarily by what?
A Nonliving stress, not infection
B Fungi and bacteria
C Viruses and nematodes
D Insects carrying pathogens
Answer: A. Nonliving stress, not infection. Abiotic disorders arise from nonliving factors such as temperature, water, nutrients or chemical injury rather than infectious pathogens.
Nutrient deficiency can resemble infection, so what is needed?
A Automatic fungicide spraying
B Immediate removal of all plants
C More irrigation in every case
D Need diagnosis before treatment
Answer: D. Need diagnosis before treatment. Nutrient problems and diseases can produce similar symptoms; diagnosis should consider plant, soil and field conditions.
How can disease incidence be recorded in a crop survey?
A Average plant height
B Amount of fertilizer applied
C Proportion of plants affected
D Weight of harvested seed
Answer: C. Proportion of plants affected. Incidence counts or estimates the proportion of plants or plant units showing disease.
Disease severity describes which feature of an affected crop?
A Number of fields planted
B Age of the crop variety
C Amount of tissue affected
D Distance to a market
Answer: C. Amount of tissue affected. Severity estimates how much plant tissue or area is affected, often using a scale or percentage.
Why should a scout record which plant parts show symptoms?
A Estimate machinery speed
B Set the seed price
C Choose a fertilizer brand
D Support disease diagnosis
Answer: D. Support disease diagnosis. Different diseases affect characteristic plant parts, and symptom location can help distinguish possible causes.
Many plant viruses spread from one crop to another through which route?
A Fertilizer dissolution
B Root nitrogen fixation
C Plant roots alone
D Vector transmission
Answer: D. Vector transmission. Many plant viruses are transmitted by vectors such as aphids, whiteflies or leafhoppers, though transmission routes vary.
Plant viruses generally require what to replicate?
A Dry seed coats only
B Dead leaves only
C Living cells for replication
D Open soil pores
Answer: C. Living cells for replication. Viruses replicate inside living host cells and depend on host cellular machinery.
Many fungal pathogens spread through which materials?
A Only mineral fertilizers
B Only clean seed
C Wind, water, and tools
D Roots of every crop
Answer: C. Wind, water, and tools. Fungal spores and other propagules can move by wind, water, contaminated tools or planting material, depending on the pathogen.
Bacterial plant pathogens may spread through which combination?
A Splash water and contaminated tools
B Clean labels and sealed bags
C Sunlight and dry air only
D Uninfected pollen only
Answer: A. Splash water and contaminated tools. Some bacterial pathogens spread in splashing water or on contaminated tools and plant material.
Disinfesting pruning tools between cuts can help accomplish what?
A Increase plant susceptibility
B Reduce mechanical pathogen spread
C Spread infected sap farther
D Replace resistant cultivars
Answer: B. Reduce mechanical pathogen spread. Cleaning or disinfesting tools can reduce transmission of pathogens that move mechanically in sap or plant debris.
Why avoid handling wet plants when disease spread by contact is possible?
A Limit contact-based spread
B Increase leaf wetness
C Improve spore production
D Delay crop emergence
Answer: A. Limit contact-based spread. Wet conditions can facilitate transfer of some pathogens on hands, clothing or tools; avoid unnecessary contact and follow crop-specific guidance.
Integrated disease management combines which approach?
A Combine compatible methods
B Depend on one fungicide
C Treat every crop alike
D Ignore host resistance
Answer: A. Combine compatible methods. IDM coordinates compatible cultural, biological, resistant-cultivar and chemical measures based on disease risk.
Which pathogen group is not controlled by fungicides as such?
A Some fungal pathogens
B Some oomycete pathogens
C Plant viruses
D Certain fungal spores
Answer: C. Plant viruses. Fungicides target susceptible fungal or oomycete pathogens; they do not directly cure plant virus infections.
Why are protectant fungicides often applied before infection occurs?
A Cure every systemic infection
B Improve seed germination
C Remove infected crop debris
D Create a barrier before infection
Answer: D. Create a barrier before infection. Protectant products form a barrier that can prevent infection when correctly timed and used according to the label.
Repeated use of one fungicide mode of action may select for what?
A Permanent crop immunity
B Faster seed germination
C Resistance among pathogen populations
D More beneficial pollinators
Answer: C. Resistance among pathogen populations. Repeated exposure can favor pathogen individuals less sensitive to that mode of action, reducing future control.
How can fungicide resistance management be supported?
A Ignore product labels
B Rotate labeled modes of action
C Repeat one product indefinitely
D Use higher rates automatically
Answer: B. Rotate labeled modes of action. Following label directions and rotating or combining modes of action when recommended can help manage resistance risk.
Biological disease control uses which type of agent?
A Unrelated synthetic fertilizers
B Only water barriers
C Suppress pathogens with living agents
D Harvest machinery
Answer: C. Suppress pathogens with living agents. Biological control uses beneficial organisms or their products to suppress particular plant pathogens.
Why remove volunteer crops or alternate hosts between seasons?
A Guarantee seed certification
B Maintain pathogens between crops
C Increase crop susceptibility
D Reduce soil drainage
Answer: B. Maintain pathogens between crops. Volunteer plants and alternate hosts can maintain some pathogens between crop cycles and serve as sources of inoculum.
After applying a disease-management measure, what should a grower do?
A Repeat treatment automatically
B Stop scouting for the season
C Assess progress before repeating treatment
D Remove healthy plants
Answer: C. Assess progress before repeating treatment. Follow-up scouting helps assess disease progress and whether another intervention is justified.