Beginner

Scientific Name
Chaetochnema pulicaria

Identification

• Small (2 mm, 1/12 in.) black beetles.
• Cause elongated scratches on the leaves.
• Transmit the Stewart’s wilt virus.
• Feeding itself does not cause yield losses.

Often Confused With
Slug feeding injury
Springtail

Period of Activity
Beetles overwinter in the top 5 cm (2 in.) of the soil/residue.  They emerge when soil temperatures reach 18°C (64°F).  The first peak of activity is in late June.  Mild winters favour beetle survival and increase the risk of Stewart’s wilt transmission. 

Scouting Notes
The highly mobile nature of this pest makes it difficult to scout and count.  While walking through the crop keep a close watch for jumping beetles or signs of feeding injury. 

Inspect at least 10 plants in each of 10 locations across the field.  Make note of the general location and approximate level of infestation.  Pay close attention to susceptible varieties, especially during the spike to 5-leaf stage.

Thresholds
Susceptible varieties may require foliar control if more than 10% of the plants have severe feeding injury or there are more than 2 beetles per plant.

Advanced

Scientific Name
Chaetochnema pulicaria

Identification
Corn flea beetles are small (2 mm or 1/12 in.), shiny black beetles that move very quickly when disturbed.  Corn flea beetles are the primary vector of the bacterial disease, Stewart’s wilt.

Adult beetles feed on corn plants causing small circular holes or elongated scratch marks on the leaves.  Feeding injury rarely causes economic losses, however Stewart’s wilt can be a serious disease of sweet corn.  Only certain varieties are susceptible to Stewart’s wilt.

Often Confused With
Slug feeding injury
Springtail

Biology
Beetles over winter in the top 5 cm (2 in.) of the soil/residue.  They emerge when soil temperatures reach 18˚C (64˚F).  Mated females lay their eggs in the soil close to the base of corn plants.  Within 6 days, eggs hatch into larvae.  The larvae feed, pupate and the adult beetles emerge from the soil.  There are three to four overlapping generations per year.

Mild winters favour the survival of the corn flea beetle and Stewart’s wilt bacteria.

Period of Activity
The first peak of activity is in late June.  First generation adults can be found in corn fields from May through July.  The threat of Stewart’s wilt transmission is highest when corn plants are at the seedling to mid-whorl stage. 

Second generation adults may be found feeding on mature corn in mid-August until frost as they prepare to overwinter.

Scouting Notes
The highly mobile nature of this pest makes it difficult to scout and count.  While walking through the crop keep a close watch for jumping beetles or signs of feeding injury.  Inspect at least 10 plants in each of 10 locations across the field.  Make note of the general location and approximate level of infestation.  Pay close attention to susceptible varieties, especially during the spike to 5-leaf stage.

Thresholds
Susceptible varieties may require foliar control if more than 10% of the plants have severe feeding injury or there are more than 2 beetles per plant.

Management Notes

• Insecticide seed treatments and varietal tolerance provide the best flea beetle control.
• Susceptibility to Stewart’s wilt varies greatly between varieties. Many early hybrids are particularly vulnerable.
• Foliar insecticides applied for cutworm control may also reduce adult flea beetle populations.
• The highly mobile nature of the beetle makes them very difficult to control with foliar insecticides.