II.) Sampling Methods

Question 1

Pest Distribution Patterns

1. )Uniform
2. )Random
3. )Clumped

Answer 1

Understanding the target pest’s distribution and ability to disperse within the sample universe is critical to developing a good program.

1. ) Uniform distribution is when the pest is evenly situated through-out the sampling universe.
2. ) Just the opposite.
3. ) Clumped distribution is when the pest tends to aggregate around specific areas in greater quantities.(plants saps, water droplets, shade, etc.).

In both clumping and random distribution scenarios, more samples are required in order to accurately estimate the pest density.

Question 2

Approaches to Sampling

Answer 2

A.) Triggers
B.) Presence-Absence
C.) Visual Injury Scales
D.) Sequential
E.) Multiple Species Monitoring 
F.) Patterns

Question 3

A.) Triggers

Answer 3

Use triggers to focus sampling during the most critical times in the lifecycle of the crop or pest e.g. biological or physical events that have a direct relationship to the host or pest.

Should occur early enough so that vulnerable stages may be treated if necessary.

For instance, tuber formation is the trigger for scouts to begin spore monitoring the Alternaria solani fungus which causes early blight disease in potatoes. Based on the sampling results fungicide applications can be made respectively.

Question 4

B.) Presence-Absence Sampling

Answer 4

Each sample unit is recorded as either infested or un-infested, regardless of the amount.

A fast and simple technique, allows the scout to note whether a pest is present or not, rather than counting each individual pest.

An especially efficient method for Arthropod pests such as thrips, aphids, white flies, and spider mites that are tiny and abundant requiring a substantial amount of time to count.

In order to be reliable this method must be based on research that correlates the proportion of infested sampling units (e.g., leaves, sticky cards) to the actual population density.

Because the absolute population densities can continue to increase after a sampling unit is “infested”, the utility of presence-absence sampling depends on the treatment threshold for the pest; and works particularly well in systems where the thresholds are well below 100% infestation.

Question 5

C.) Visual injury scales

Answer 5

A visual injury scale that the sampler can read only pair with the no levels of the station.

It is useful to have a standard for comparison to avoid overestimating or under estimated damage.

Question 6

D.) Sequential sampling

Answer 6

A method for efficiently concentrating sampling efforts where they will provide most benefit.

This method requires fewer samples to arrive at a decision with the same degree of certainty as standard sampling.

As opposed to taking a fixed number of samples per field; in sequential sampling, the number of samples taken at each visit depends on past densities; samples are taken only until the accumulated results concretely describe a pest population with relation to its threshold.

Question 7

E.) Monitoring multiple species

Answer 7

Monitoring multiple pests and beneficial species at the same time can increase sampling efficiency.

Tools such as GPS,GIS, PDAs (personal digital assistant’s) and smart phones are useful toward electronically sampling pest/s in the field.

Question 8

F.) Sampling patterns

Answer 8

a. ) Random
b. ) Stratified
c. ) Systematic

Different patterns for different objectives; both are sampling it is important that the patterns remain unbiased.

Question 9

Fa.) Random sampling

Answer 9

The most common of sampling patterns.

Every sample unit as an equal chance of selection. The sampler has to avoid favoring certain sample types that may skew the results such as the easiest plants to reach, ripest crops, or the most damaged plants.

Shapes such as U, X, Y, or W are often walked in the fields to ensure a random pattern.

Question 10

Fb.) Stratified sample

Answer 10

Partitions the sampling universe into subunits that vary in character. Each sub unit (Stratum)is then treated independently.

This may include areas of differing elevation, moisture content, soil types, North vs South facing, etc.

This method helps to recognize habitats where the pest shall not be found, so as to be excluded from future sampling runs.

Further examples include treating field edges separately from the centers.

Question 11

Fc.) Systematic sampling

Answer 11

Is used wisely because of it’s ease to implement.

Examples include sampling every 50th plant, taking a sample every 3 feet in a row, etc.

Is appropriate when the sampling universe is relatively homogeneous.