ILLINOIS FIELD CROPS APPLICATOR STUDY GUIDE 2025/2026
QUESTIONS WITH ANSWERS GRADED A+
✔✔What kind of damage does black cutworm larvae do to corn seedlings? - ✔✔young -
chew holes in leaves
older - cut plants
✔✔What types of field factors increase the potential for black cutworm damage to
develop and why? - ✔✔- crop debris
- winter annual weeds
- late planted
✔✔What is the recommended methods for managing black cutworms in Illinois? -
✔✔apply a rescue treatment when 3% or more plants are cut
*preventative treatments not effective*
✔✔What type of damage does larval European corn borer cause? - ✔✔- feed within the
whorl causing "shot holes" in the leaves
- ear tunneling and stalk tunneling
✔✔What type of damage does corn leaf aphid cause? - ✔✔honeydew coats the tassel
and possibly the silks reducing pollination
✔✔describe wireworms and their damage - ✔✔Appearance: larvae are yellow to
reddish-brown, hard shelled and wire like
Damage: tunnel into seeds and seedlings below soil level
✔✔What do Japanese beetle grubs and other white grubs look like? - ✔✔Full grown
larvae are white, C-shaped, and about one inch long
✔✔How are Japanese beetle grub species identified - ✔✔the pattern of bristle-like
setae on the end of the abdomen, called the raster pattern
✔✔What kind of damage do Japanese beetle grubs cause? - ✔✔- chew on roots and
root hairs of seedlings
- results in irregular emergence, reduced stands and stunted or wilted plants
- injured plants may turn purple because they cannot take up phosphorous efficiently
✔✔What do Japanese beetle adults look like? - ✔✔Metallic green beetles that are 3/8
to 1/2 inch long with coppery wing covers
✔✔What kind of damage do japanese beetle adults cause - ✔✔clip silks on corn ears
THRESHOLD- silks clipped to within 1/2" of ear
, ✔✔describe the appearance of adult bean leaf beetles - ✔✔- orange, yellow, red or
gray
- dark triangle behind head always present
- usually spots and stripes on wing covers
✔✔what type of injury do bean leaf beetles cause to soybean plants at different times
throughout the growing season? - ✔✔- feed on cotyledons and first true leaves
- chew holes in leaves during the vegetative growth stage
- feeding during pod filling
✔✔describe soybean aphids and where they occur - ✔✔pinhead-sized, yellow, soft
bodied, round insects on the underside of soybean leaves
✔✔what kind of damage do soybean aphids cause? - ✔✔- they suck sap from soybean
plants causing leaves to crinkle or cup and turn yellow
- they excrete honeydew, a sugary substance consisting of excess plant sap taken up
by the aphid while feeding
- sooty mold, a blackish mold that grows on the honeydew, reducing photosynthesis
-heavy infestations may cause a reduction in the number of pods
- they are capable of transmitting several viruses
✔✔what kind of damage do spider mites cause to soybean plants - ✔✔- stippling leaves
- fine silk on leaves and between plants
- bronzing leaves
- curled leaves and leaf drop
✔✔Describe the appearance of alfalfa weevil LARVAE? - ✔✔-up to 1/2" long
- green with white stripe down back
- dark head
✔✔Describe the appearance of alfalfa weevil ADULT? - ✔✔- 1/4" long
- medium brown with dark brown stripe
- hard wing covers
✔✔What kind of damage does alfalfa weevil cause? - ✔✔- larvae skeletonize leaves,
causing fields to appear "frosted"
- adults "feather" the leaves and chew on stems
Economic Thresholds:
-at first cutting: >3 larvae per stem and 20% of the tips skeletonized
-later cuttings: feeding on 50% of crowns and no regrowth for 3-6 days
✔✔describe the appearance of potato leafhopper - ✔✔green wedge shaped about 1/8
inch long
QUESTIONS WITH ANSWERS GRADED A+
✔✔What kind of damage does black cutworm larvae do to corn seedlings? - ✔✔young -
chew holes in leaves
older - cut plants
✔✔What types of field factors increase the potential for black cutworm damage to
develop and why? - ✔✔- crop debris
- winter annual weeds
- late planted
✔✔What is the recommended methods for managing black cutworms in Illinois? -
✔✔apply a rescue treatment when 3% or more plants are cut
*preventative treatments not effective*
✔✔What type of damage does larval European corn borer cause? - ✔✔- feed within the
whorl causing "shot holes" in the leaves
- ear tunneling and stalk tunneling
✔✔What type of damage does corn leaf aphid cause? - ✔✔honeydew coats the tassel
and possibly the silks reducing pollination
✔✔describe wireworms and their damage - ✔✔Appearance: larvae are yellow to
reddish-brown, hard shelled and wire like
Damage: tunnel into seeds and seedlings below soil level
✔✔What do Japanese beetle grubs and other white grubs look like? - ✔✔Full grown
larvae are white, C-shaped, and about one inch long
✔✔How are Japanese beetle grub species identified - ✔✔the pattern of bristle-like
setae on the end of the abdomen, called the raster pattern
✔✔What kind of damage do Japanese beetle grubs cause? - ✔✔- chew on roots and
root hairs of seedlings
- results in irregular emergence, reduced stands and stunted or wilted plants
- injured plants may turn purple because they cannot take up phosphorous efficiently
✔✔What do Japanese beetle adults look like? - ✔✔Metallic green beetles that are 3/8
to 1/2 inch long with coppery wing covers
✔✔What kind of damage do japanese beetle adults cause - ✔✔clip silks on corn ears
THRESHOLD- silks clipped to within 1/2" of ear
, ✔✔describe the appearance of adult bean leaf beetles - ✔✔- orange, yellow, red or
gray
- dark triangle behind head always present
- usually spots and stripes on wing covers
✔✔what type of injury do bean leaf beetles cause to soybean plants at different times
throughout the growing season? - ✔✔- feed on cotyledons and first true leaves
- chew holes in leaves during the vegetative growth stage
- feeding during pod filling
✔✔describe soybean aphids and where they occur - ✔✔pinhead-sized, yellow, soft
bodied, round insects on the underside of soybean leaves
✔✔what kind of damage do soybean aphids cause? - ✔✔- they suck sap from soybean
plants causing leaves to crinkle or cup and turn yellow
- they excrete honeydew, a sugary substance consisting of excess plant sap taken up
by the aphid while feeding
- sooty mold, a blackish mold that grows on the honeydew, reducing photosynthesis
-heavy infestations may cause a reduction in the number of pods
- they are capable of transmitting several viruses
✔✔what kind of damage do spider mites cause to soybean plants - ✔✔- stippling leaves
- fine silk on leaves and between plants
- bronzing leaves
- curled leaves and leaf drop
✔✔Describe the appearance of alfalfa weevil LARVAE? - ✔✔-up to 1/2" long
- green with white stripe down back
- dark head
✔✔Describe the appearance of alfalfa weevil ADULT? - ✔✔- 1/4" long
- medium brown with dark brown stripe
- hard wing covers
✔✔What kind of damage does alfalfa weevil cause? - ✔✔- larvae skeletonize leaves,
causing fields to appear "frosted"
- adults "feather" the leaves and chew on stems
Economic Thresholds:
-at first cutting: >3 larvae per stem and 20% of the tips skeletonized
-later cuttings: feeding on 50% of crowns and no regrowth for 3-6 days
✔✔describe the appearance of potato leafhopper - ✔✔green wedge shaped about 1/8
inch long
