Spring Larva Sampling Protocal
Rating Cutworm Damage
Cutworm larvae are difficult to monitor in cropland situations.
Small cutworms are well camouflaged in soil. Searching for
the larvae within a square foot or row-foot soil sample can be extremely
time consuming. However, populations
may be assessed by how frequently larvae are found and how widespread their
occurrence. For example, Alfalfa
and cereal grains are less susceptible to cutworm damage than sugarbeets.
Rating cutworms on a wider scale e.g. countywide basis can
help to determine relative population and risk to each crop.
(Sue Blodgett and Will Lanier, IPM 994-5690)
How do you extract cutworms or calculate the sq ft counts?
Scrape away the soil to @2 inches.
Per foot means a Row Foot calculation. So scrape away the soil for a foot
right down the row.
Time of day or if it is bright or cloudy will affect the activity of cutworms.
Pale Western are more light adverse than Army cutworms. Pale Western feed
below ground (more damageing), Army cutworm feed above.
What are the size categories for cutworms?
Army cutworms (mostly over witner as worms, so they will be mature earlier
in the spring):
High Potential: Larval Size <= 0.5in
Medium Potential: 0.5in < Larval Size <= 1.0in
Low Potential: Larval Size > 1.0in
Pale Western cutworms (mostly overwinter as eggs, so they will be later
to mature in the spring):
High Potential: Larval Size <= 0.5in
Medium Potential: 0.5in < Larval Size <= 1.0in
Low Potential: Larval Size > 1.0in
How many samples do I take?
When in doubt take more, or if any of the first 5 samples compared to each
other, vary twice as much as the threshold take 5 more samples, if they don't
stop and go to the next field. The goal is to try and estimate the areas of
the field at risk to cutworm activity.
Rating Scale of Army and Pale Western Cutworm Larval Infestations in
the Spring
1 - Not
present or very difficult to find
2 - Present
but not found frequently
3 - Commonly
seen but no local economic infestations in alfalfa (ACW) or wheat (ACW, PWC);
Economic infestations may be present in sugarbeets.
4 - Commonly
found but limited economic infestations / treatments in alfalfa or wheat
(less than 1% of fields require treatment). Economic infestations likely
in sugarbeets.
5 - Commonly
found with significant economic infestations in alfalfa or wheat (approximately
10% of fields require treatment).
6 - Widespread
economic infestations (more than 20% of fields require treatment).
(Contributed by Gary Hein, University of Nebraska).