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OK Pesticide Applicator study materials
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OK Pesticide Applicator practice questions

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Question 1Core - laws, safety, equipment and knowledge required in all categories

The signal word on a pesticide label is based mainly on the product's:

  1. persistence in soil
  2. acute toxicity Correct answer.
  3. cost per acre
  4. odor strength

Explanation

Signal words reflect the product's acute toxicity as determined from oral, dermal, and inhalation LD50 values and from eye and skin irritation studies. They are a hazard communication tool for the user. Environmental persistence, price, and odor are not the basis for the signal word.

Question 2Core - laws, safety, equipment and knowledge required in all categories

Which Oklahoma state agency is the lead agency for pesticide regulation?

  1. Oklahoma State Department of Health
  2. Agriculture, Food, and Forestry Department Correct answer.
  3. Oklahoma Corporation Commission
  4. Oklahoma Department of Wildlife Conservation

Explanation

The Oklahoma Department of Agriculture, Food, and Forestry administers the state pesticide law, including applicator certification and pesticide use regulation. Other state agencies have narrower roles in health, wildlife, or utilities.

Question 3Core - laws, safety, equipment and knowledge required in all categories

A restricted-use pesticide may be applied by a noncertified person only when the person is:

  1. licensed by the county extension office
  2. wearing a respirator during the entire application
  3. diluting the product before application
  4. under certified applicator supervision Correct answer.

Explanation

Restricted-use pesticides may be used by certified applicators or by persons working under their direct supervision when the label allows it. The certified applicator remains responsible for the application. Dilution, respirator use, or a county office license does not substitute for certification.

Question 4Core - laws, safety, equipment and knowledge required in all categories

Which material is generally preferred for pesticide handling gloves?

  1. Wool-lined winter glove
  2. Untreated leather work glove
  3. Absorbent cotton canvas glove
  4. Chemical-resistant rubber Correct answer.

Explanation

Chemical-resistant materials such as rubber resist penetration by many pesticide formulations and can be rinsed after use. Leather, cotton, and wool absorb liquids and can hold pesticide against the skin for long periods.

Question 5Core - laws, safety, equipment and knowledge required in all categories

If pesticide gets in a person's eyes, the first step is to:

  1. flush with water for at least 15 minutes Correct answer.
  2. apply a soothing eye ointment
  3. rub the eye to remove the chemical
  4. wait to see whether irritation develops

Explanation

Immediate flushing with clean water for at least 15 minutes is the standard first aid for pesticide exposure to the eyes. Medical help should be sought as directed by the label. Rubbing or applying ointments can worsen injury.

Question 6Core - laws, safety, equipment and knowledge required in all categories

Under FIFRA, certified applicators must keep records of restricted-use pesticide applications for at least:

  1. 1 year
  2. 5 years
  3. 10 years
  4. 2 years Correct answer.

Explanation

Federal regulations require certified applicators to keep records of restricted-use pesticide applications for at least two years from the date of application. Some state requirements may be longer, but the federal minimum is two years.

Question 7Core - laws, safety, equipment and knowledge required in all categories

Before a pesticide container is recycled or disposed of, it should be:

  1. buried near the mixing site
  2. filled with water and stored
  3. burned in the field
  4. triple-rinsed and drained Correct answer.

Explanation

Empty pesticide containers must be triple-rinsed or pressure-rinsed and drained so that the rinse water can be added to the spray tank. Proper rinsing removes most residue and prepares the container for recycling or approved disposal. Burning or burying containers is not an acceptable practice.

Question 8Core - laws, safety, equipment and knowledge required in all categories

The first step in an integrated pest management program is to:

  1. spray on a calendar schedule
  2. apply a broad-spectrum insecticide
  3. increase the application rate
  4. identify and monitor the pest Correct answer.

Explanation

IPM begins with correct pest identification and monitoring so that control decisions are based on pest presence and economic thresholds. Chemical control is used only when other tactics are insufficient. Calendar spraying and routine rate increases are not IPM practices.

Question 9Core - laws, safety, equipment and knowledge required in all categories

Two pesticides have oral LD50 values of 50 mg/kg and 500 mg/kg. Which statement is correct?

  1. LD50 does not measure acute toxicity.
  2. The 500 mg/kg product is more acutely toxic.
  3. Both products have equal acute toxicity.
  4. The 50 mg/kg product is more acutely toxic. Correct answer.

Explanation

The LD50 is the dose that kills 50 percent of test animals; a lower value means a smaller dose causes death, so the product is more acutely toxic. Therefore 50 mg/kg is more toxic than 500 mg/kg. LD50 is a standard measure of acute toxicity.

Question 10Core - laws, safety, equipment and knowledge required in all categories

A label states a 14-day preharvest interval for a crop. This means the applicator must:

  1. do not harvest for 14 days after application Correct answer.
  2. wait 14 days after harvest before applying again
  3. reapply the product every 14 days
  4. apply no more than 14 days before planting

Explanation

The preharvest interval is the minimum time that must pass between the last pesticide application and harvest. It protects consumers and ensures residues do not exceed tolerances. It does not refer to planting dates or reapplication frequency.

Question 11Core - laws, safety, equipment and knowledge required in all categories

A restricted-entry interval on a label requires that:

  1. workers stay out until the interval has ended Correct answer.
  2. workers must wear gloves for a full 24 hours
  3. the treated field must be irrigated afterward
  4. workers stay out only while spraying is underway

Explanation

The restricted-entry interval is the time after application during which entry into the treated area is restricted, except for persons allowed by the label with required PPE. It continues after spraying stops. It does not require irrigation or a fixed 24-hour glove rule.

Question 12Core - laws, safety, equipment and knowledge required in all categories

Spraying during a temperature inversion is risky because:

  1. the spray solution becomes too thick
  2. fine droplets can drift off-site Correct answer.
  3. droplets evaporate before landing
  4. wind speed is always too high

Explanation

In an inversion, a layer of cool air near the ground is trapped under warmer air, so small droplets can remain suspended and move laterally with air movement. This can cause off-target drift even when the surface wind seems calm. Inversions are not defined by high wind or spray thickening.

Question 13Core - laws, safety, equipment and knowledge required in all categories

If a spray nozzle becomes worn, the most likely result is:

  1. lower output and a finer pattern
  2. higher output and a poorer pattern Correct answer.
  3. no change in output or pattern
  4. automatic pressure compensation

Explanation

Worn nozzles usually have enlarged orifices, which increase flow and distort the spray pattern. This can cause overapplication and uneven coverage. Nozzles should be replaced when output or pattern deviates from specifications.

Question 14Core - laws, safety, equipment and knowledge required in all categories

To prevent back-siphoning when filling a spray tank, an applicator should:

  1. use a higher pump pressure
  2. keep the hose outlet above the tank liquid Correct answer.
  3. add the pesticide before the water
  4. submerge the fill hose completely in the tank

Explanation

An air gap between the water hose outlet and the tank liquid prevents pesticide solution from being drawn back into the water supply. This is a simple and effective anti-siphoning method. Submerging the hose or increasing pressure does not provide backflow protection.

Question 15Core - laws, safety, equipment and knowledge required in all categories

Pesticides should be stored:

  1. in an open shed with windows
  2. locked and ventilated, away from food Correct answer.
  3. near livestock feed for easy access
  4. in clean food containers for convenience

Explanation

Pesticide storage areas should be locked, ventilated, and separated from food, feed, and living areas to prevent accidental exposure. Keeping products in original labeled containers also prevents misidentification. Food containers and feed areas are unsafe storage locations.

Question 16Core - laws, safety, equipment and knowledge required in all categories

During a pesticide spill, the first priority is to:

  1. notify the manufacturer
  2. wash the spill into a nearby storm drain
  3. cover the spill with soil
  4. protect people and stop the spill source Correct answer.

Explanation

Spill response begins with protecting people from exposure and stopping the source of the release if it can be done safely. Containment and cleanup follow. Washing a spill into a storm drain can spread contamination to water resources.

Question 17Core - laws, safety, equipment and knowledge required in all categories

To reduce the development of pesticide resistance, an applicator should:

  1. use the same product at higher rates
  2. rotate modes of action and use nonchemical controls Correct answer.
  3. apply more frequently
  4. mix two products that share the same mode of action

Explanation

Resistance management relies on diversifying selection pressure, such as rotating pesticide modes of action and integrating cultural, biological, or mechanical controls. Repeated use of the same mode of action, especially at higher rates or frequencies, accelerates resistance.

Question 18Core - laws, safety, equipment and knowledge required in all categories

Which situation most increases the risk of pesticide leaching to groundwater?

  1. applying a granular product to turfgrass
  2. applying to a steep slope with heavy runoff
  3. a tight clay soil with very low rainfall
  4. sandy soil and a high water table Correct answer.

Explanation

Leaching is favored by coarse, sandy soils with low organic matter, high water tables, and mobile pesticides. These conditions allow water to carry the pesticide downward. Steep slopes mainly increase runoff risk rather than leaching.

Question 19Core - laws, safety, equipment and knowledge required in all categories

Under the Worker Protection Standard, agricultural employers must provide:

  1. respirators for every worker in the crew
  2. a paid vacation after each application
  3. pesticide-free clothing for every worker on site
  4. safety training and decontamination supplies Correct answer.

Explanation

The Worker Protection Standard requires pesticide safety training for agricultural workers and handlers and requires decontamination supplies to be available. PPE requirements are based on the label and task, not a blanket rule for every worker.

Question 20Core - laws, safety, equipment and knowledge required in all categories

When transporting pesticides in a vehicle, the products should be:

  1. stored with food and drinks
  2. placed in the passenger seat
  3. secured in the cargo area to prevent spills Correct answer.
  4. carried unsecured in an open truck bed with tools

Explanation

Pesticides should be secured in a cargo area where they cannot tip, spill, or contaminate the passenger compartment. Keeping them away from food, drinks, and tools reduces the risk of accidental exposure and contamination.

Question 21Core - laws, safety, equipment and knowledge required in all categories

An applicator wants to use a pesticide at a rate lower than the label allows for a pest not listed on the label. Under FIFRA, this use is:

  1. always allowed at any rate on any labeled or unlabeled site
  2. never allowed under any circumstances
  3. allowed if the site is on the label and not prohibited Correct answer.
  4. allowed only for restricted-use products

Explanation

FIFRA allows certain uses that differ from the label, including a lower application rate or use against a pest not listed, if the application site is on the label and the label does not prohibit the use. This is often called a Section 2(ee) use. It is not unlimited and does not apply only to restricted-use products.

Question 22Core - laws, safety, equipment and knowledge required in all categories

An applicator with a tight-fitting half-face respirator must be:

  1. exempt if application lasts under an hour
  2. fit-tested and medically evaluated before use Correct answer.
  3. able to use cartridges until odor breaks through
  4. allowed with a beard if straps are tight

Explanation

Tight-fitting respirators require a medical evaluation and fit testing before use. Facial hair that interferes with the seal is not allowed. Cartridges must be changed according to the manufacturer's schedule or when breakthrough occurs, not simply when odor is noticed.

Question 23Core - laws, safety, equipment and knowledge required in all categories

Before applying an outdoor pesticide near a listed species habitat, the applicator should:

  1. apply only when the wind is calm
  2. check the label and county bulletins for limits Correct answer.
  3. ignore the label if the pest is severe
  4. apply at a much higher rate to reduce repeat trips

Explanation

Pesticide labels and associated endangered species bulletins may impose buffer zones, timing restrictions, or other limits to protect listed species. The applicator is responsible for checking these restrictions before use. Calm wind alone does not satisfy endangered species requirements.

Question 24Core - laws, safety, equipment and knowledge required in all categories

Two applicators use the same pesticide. One wears full PPE and the other wears shorts and a t-shirt. The second applicator has a greater:

  1. the LD50 value of the pesticide product
  2. the signal word printed on the label
  3. the acute toxicity of the pesticide product
  4. higher risk because exposure is greater Correct answer.

Explanation

Toxicity is an inherent property of the pesticide, but risk depends on both toxicity and exposure. Wearing less PPE increases exposure, so the risk of poisoning is higher even though the product and its LD50 are the same.

Question 25Core - laws, safety, equipment and knowledge required in all categories

Before mixing two pesticides in the same tank, an applicator should:

  1. skip agitation during mixing
  2. do a jar test for compatibility Correct answer.
  3. add both products at their full label rates
  4. use hot water only

Explanation

A jar test uses small amounts of the products and carrier water to check whether they mix without thickening, settling, or separating. This helps prevent tank-mix failures that can clog equipment or reduce efficacy. Agitation and correct mixing order are also important.

Question 26Core - laws, safety, equipment and knowledge required in all categories

A pesticide label displays the signal word "WARNING." Under EPA labeling requirements, this places the product in which toxicity category?

  1. Category IV - practically nontoxic
  2. Category III - slightly toxic
  3. Category I - highly toxic
  4. Category II - moderately toxic Correct answer.

Explanation

EPA groups pesticide products into four toxicity categories based on acute oral, dermal, inhalation, and eye/skin irritation data. Category I carries the signal word DANGER (with POISON and a skull-and-crossbones if highly toxic by the oral, dermal, or inhalation route), Category II uses WARNING, Category III uses CAUTION, and Category IV also uses CAUTION.

Question 27Agricultural Plant (1a) and Agricultural Animal (1b)

On a pesticide label, the preharvest interval (PHI) states the:

  1. Time from last application to harvest Correct answer.
  2. Time workers must wait before reentering the field
  3. Interval between successive sprays on the same crop
  4. Maximum number of applications allowed per season

Explanation

The preharvest interval is the minimum number of days that must pass between the final application and the harvest of the crop. It exists so that residues in the harvested commodity stay within the established tolerance. Applicators who shorten the PHI risk an illegal residue in the marketed crop.

Question 28Agricultural Plant (1a) and Agricultural Animal (1b)

The restricted-entry interval (REI) printed on a label is intended mainly to protect:

  1. Wildlife that feeds along field edges
  2. Workers who enter the treated area Correct answer.
  3. Groundwater beneath the treated field
  4. Consumers who buy the harvested crop

Explanation

The REI is the period after an application during which entry into the treated area is restricted, with the goal of limiting worker exposure to residues while they are still at hazardous levels. It applies to occupational entry, not to the consumer or to environmental receptors.

Question 29Agricultural Plant (1a) and Agricultural Animal (1b)

Under federal and state rules, a person must be a certified applicator, or work under the direct supervision of one, to buy and use:

  1. Only products labeled for aquatic sites
  2. Any general-use herbicide sold in the state
  3. Pesticides classified as restricted use Correct answer.
  4. Any product applied with a power sprayer

Explanation

Restricted-use pesticides carry a higher risk of harm to people or the environment, so sale and use are limited to certified applicators or persons under their direct supervision. General-use products do not carry that certification requirement. The classification is set on the label, not by the equipment used.

Question 30Agricultural Plant (1a) and Agricultural Animal (1b)

When mixing a concentrated pesticide, the label most commonly requires which personal protective equipment?

  1. Safety glasses and canvas work gloves
  2. Chemical-resistant gloves and eyewear Correct answer.
  3. A dust mask and cotton coveralls
  4. A hard hat and steel-toed boots

Explanation

Handling the concentrate is the highest-exposure task in most operations, so labels typically call for chemical-resistant gloves plus eye protection during mixing and loading. Coveralls may also be required, but gloves and eye protection are the baseline.

Question 31Agricultural Plant (1a) and Agricultural Animal (1b)

Before any pesticide is applied to a crop, the applicator's first step should be to:

  1. Read the label and follow all directions Correct answer.
  2. Check the pressure gauge on the sprayer
  3. Notify neighbors who live within one mile
  4. Mix a small test batch in an open bucket

Explanation

The label is the legal and practical instruction set for the product, covering rates, timing, PPE, restrictions, and precautions. Every other action, including calibration and mixing, should follow from what the label requires.

Question 32Agricultural Plant (1a) and Agricultural Animal (1b)

Applying a broadcast spray when the wind is strong is most likely to result in:

  1. Clogging of the sprayer screens
  2. Drift onto neighboring fields Correct answer.
  3. Faster uptake by the crop leaves
  4. Less nozzle wear during the pass

Explanation

Wind carries fine droplets away from the target area, and the greater the wind speed the farther those droplets travel. Apart from being wasteful, off-target movement can injure sensitive crops, harm pollinators, and create liability. Labels specify maximum allowable wind conditions for this reason.

Question 33Agricultural Plant (1a) and Agricultural Animal (1b)

Certified applicators are generally required to keep records of restricted-use pesticide applications for at least:

  1. 30 days after the application
  2. Two years after the application Correct answer.
  3. Ten years after the application
  4. One year after the application

Explanation

Federal regulation, adopted in state programs, sets a minimum two-year retention period for records of restricted-use pesticide applications. Records include the product, rate, date, location, and the certified applicator responsible. Some labels or state rules may require longer retention.

Question 34Agricultural Plant (1a) and Agricultural Animal (1b)

The proper way to handle an emptied pesticide container is to:

  1. Burn the container in the field after it dries
  2. Fill the container once with water and drain it
  3. Triple rinse and add the rinsate to the tank Correct answer.
  4. Crush the container and bury it on the farm

Explanation

Triple rinsing removes most of the residual product from the container, and putting the rinsate back into the spray tank uses that residue on the labeled site. The rinsed container can then be handled through the container-recycling program. Burying or burning containers is not an acceptable disposal method.

Question 35Agricultural Plant (1a) and Agricultural Animal (1b)

With nozzles unchanged, raising the pressure on a hydraulic sprayer will:

  1. Lower boom pressure and cause streaks
  2. Raise the flow rate with no change in droplet size
  3. Lower the flow rate and make coarser spray
  4. Raise the flow rate and make finer droplets Correct answer.

Explanation

Nozzle output rises roughly with the square root of pressure, and higher pressure also shears the liquid into smaller droplets. That combination increases both the applied volume and the drift potential. Changing rate should be done by nozzle selection or speed, not by large pressure swings.

Question 36Agricultural Plant (1a) and Agricultural Animal (1b)

The most dependable way to slow the development of pesticide resistance in a pest population is to:

  1. Keep using one product until it fails completely
  2. Rotate products with different modes of action Correct answer.
  3. Spray more often at a reduced label rate
  4. Apply the same product at a higher rate

Explanation

Resistance spreads when the same mode of action is used repeatedly, selecting for individuals that survive it. Rotating among products with different modes of action, and using nonchemical tactics, reduces that selection pressure. Rate changes and more frequent applications of one product accelerate the problem.

Question 37Agricultural Plant (1a) and Agricultural Animal (1b)

2,4-D and dicamba injure broadleaf weeds because these herbicides act as:

  1. Inhibitors of amino acid synthesis
  2. Photosynthesis inhibitors
  3. Synthetic plant hormones (auxins) Correct answer.
  4. Cell membrane disruptors

Explanation

Both products are synthetic auxins that mimic natural plant growth hormones, causing uncontrolled growth, twisting, and death of susceptible broadleaf plants. Grasses are largely unaffected, which gives the selectivity used in cereal and pasture settings. Off-target movement of these products is a major concern for nearby broadleaf crops.

Question 38Agricultural Plant (1a) and Agricultural Animal (1b)

A protectant fungicide gives the best disease control when it is applied:

  1. After symptoms are widespread in the field
  2. At the end of the season before harvest
  3. Only when the disease passes threshold
  4. Before the pathogen infects the plant Correct answer.

Explanation

Protectant materials form a barrier on the leaf surface and must be in place before spores germinate and penetrate. Once the fungus is inside the tissue they cannot eradicate it. This is why protectant programs are timed to weather and disease forecasts rather than to visible symptoms.

Question 39Agricultural Plant (1a) and Agricultural Animal (1b)

A pour-on insecticide for cattle is normally applied:

  1. In a strip along the animal's backline Correct answer.
  2. As a fine mist over the whole herd
  3. By deep injection into the neck muscle
  4. To the hooves and lower legs only

Explanation

Pour-on formulations are designed to be run in a measured strip down the midline of the back, where the material spreads over the hide. Applying them by other routes wastes product and may violate the label. Dose is calculated from animal body weight.

Question 40Agricultural Plant (1a) and Agricultural Animal (1b)

A milk withholding statement on a livestock insecticide label tells the producer:

  1. How often the product may be reapplied
  2. How long the product stays effective after treatment
  3. How much product each animal should get
  4. How long milk must be kept out of the bulk tank Correct answer.

Explanation

The milk withholding time is the interval after treatment during which milk from treated animals cannot be sold. It ensures residues in milk remain below the tolerance. Selling milk inside that window creates an adulterated product and a legal violation.

Question 41Agricultural Plant (1a) and Agricultural Animal (1b)

Feed-through insecticides such as diflubenzuron control horn flies by:

  1. Stopping larvae from developing in manure Correct answer.
  2. Repelling adult flies from the animal's coat
  3. Sterilizing adult flies that feed on the animal
  4. Killing adult flies that land on the hide

Explanation

These products are consumed with feed or mineral and pass through the animal largely unchanged, so the manure becomes toxic to developing fly larvae. Because the target stage is the larva in the dung pat, control depends on consistent consumption by the whole herd.

Question 42Agricultural Plant (1a) and Agricultural Animal (1b)

Insecticide-impregnated ear tags are used mainly to control:

  1. Horn flies and face flies on cattle Correct answer.
  2. Lice on the tail head and shoulders
  3. Ticks on the legs and belly
  4. Internal parasites in the stomach

Explanation

Ear tags release insecticide slowly and are most effective against flies that feed on or around the head and back of cattle. Because the active ingredient is concentrated near the head, tags do not control pests on the lower body or internal parasites. Rotating tag chemistries helps delay fly resistance.

Question 43Agricultural Plant (1a) and Agricultural Animal (1b)

Which practice best reduces honey bee exposure when a flowering crop must be treated?

  1. Raise the rate so the residue fades sooner
  2. Spray in the evening when bees are quiet Correct answer.
  3. Spray at midday when the field is dry
  4. Add a spreader-sticker to the tank mix

Explanation

Bees forage mainly during daylight, so evening applications let the residue dry and weather before the next foraging period. The label may also state specific bee precautions, such as not applying during bloom. Adding adjuvants or raising the rate does not reduce bee hazard.

Question 44Agricultural Plant (1a) and Agricultural Animal (1b)

A nonionic surfactant is added to a spray tank mainly to:

  1. Raise the pH of the spray solution
  2. Increase the thickness of the mixture
  3. Neutralize minerals in hard water
  4. Help the spray wet and spread on leaves Correct answer.

Explanation

Surfactants lower the surface tension of the spray droplet so it spreads across the waxy leaf surface instead of beading up. Better coverage usually means better uptake of the active ingredient. Buffer and water-conditioning products serve the pH and hardness functions.

Question 45Agricultural Plant (1a) and Agricultural Animal (1b)

A spray nozzle should usually be replaced when its output deviates from the rated flow by more than:

  1. 2 percent
  2. 10 percent Correct answer.
  3. 50 percent
  4. 25 percent

Explanation

Worn nozzles commonly go unnoticed because the pattern still looks acceptable, so flow is checked against the rated output. A deviation of about 10 percent is the usual replacement threshold in calibration programs. Larger errors mean the applied rate and pattern are no longer reliable.

Question 46Agricultural Plant (1a) and Agricultural Animal (1b)

A sprayer is calibrated before each season primarily to:

  1. Reduce wear on the sprayer pump seals
  2. Shorten the time needed to fill the tank
  3. Confirm the intended rate is applied evenly Correct answer.
  4. Increase the pressure available at the boom

Explanation

Calibration determines the actual output per acre so the tank mix can be built to deliver the labeled rate. It also reveals worn nozzles and uneven patterns that cause streaks. Applying an unverified rate can mean poor control or an illegal over-application.

Question 47Agricultural Plant (1a) and Agricultural Animal (1b)

Spraying during a temperature inversion is hazardous because:

  1. Nozzles clog more often in calm air
  2. The spray dries on leaves before it is absorbed
  3. Fine droplets can drift far off target Correct answer.
  4. The pesticide degrades faster in cool air

Explanation

In an inversion, a layer of cool air is trapped under warmer air, so small droplets released near the surface do not disperse upward. They can travel long distances in a concentrated mass and settle far from the application site. Inversions are common in early morning and evening with clear skies and light wind.

Question 48Agricultural Plant (1a) and Agricultural Animal (1b)

Which situation is most likely to produce an illegal pesticide residue in meat?

  1. Selling a cull cow before withdrawal ends Correct answer.
  2. Pouring on along the animal's backline
  3. Treating beef cattle with an approved product
  4. Applying a product at its labeled rate

Explanation

Every livestock product carries a meat withdrawal time, and marketing an animal before that interval expires leaves residues above tolerance. Approved products, labeled rates, and correct application methods do not by themselves create illegal residues. The violation comes from ignoring the withdrawal period.

Question 49Agricultural Plant (1a) and Agricultural Animal (1b)

Fumigation of stored grain with phosphine is effective only when the bin is:

  1. Kept below freezing for several days
  2. Vented to the outside during treatment
  3. Sealed gas-tight for the exposure period Correct answer.
  4. Filled with grain at high moisture content

Explanation

Phosphine is a gas that must be held at a lethal concentration long enough to kill all life stages present, which requires a gas-tight structure. Leaks dilute the gas and produce survivors, which is a major route to resistance. High moisture grain is a separate quality and spoilage problem, not a requirement for fumigation.

Question 50Agricultural Plant (1a) and Agricultural Animal (1b)

Which set of factors most strongly determines how long a herbicide remains active in soil?

  1. Soil organic matter and soil moisture Correct answer.
  2. The size and shape of the spray tank
  3. The time of day the application is made
  4. The color and odor of the spray mixture

Explanation

Soil persistence depends mainly on how tightly the herbicide binds to organic matter and clay and on how much microbial and chemical breakdown occurs, both of which are driven by moisture and temperature. Persistence governs whether a sensitive rotational crop can be planted the following season.