Tuber Flea Beetle

Causal Organisms: Three different species have been found in Alberta (Epitrix cucumeris, E. subcrinata, E. tuberis)

Crops Affected: potatoes

Life Cycle:

• Of the 3 species found in Alberta, only tuberis is known to cause serious damage to tubers
• Adults are small (up to 2mm long), black beetles that jump when disturbed
  • Adults can fly
    • They may move this way into new potato fields
  • Adults feed on the potato foliage (leaves), resulting in leaves that have a characteristic “shot hole” appearance
    • The leaves look a bit like they were shot with a shotgun, having a pattern of holes scattered across the blade of the leaflet
    • The flea beetles are more frequently found on the underside of the leaves
    • Damage from adult feeding is not usually economically significant (does not affect yields), however high populations of adults can defoliate and kill young plants
  • Larvae are slim, white, and up to 5mm long
    • Larval feeding on roots and tubers is a major concern to potato growers in some areas
    • Damage by larval feeding is not detected until after harvest, during the peeling process
  • Flea beetle adults overwinter in the soil, in and around potato fields
    • Their survival is increased in elevated areas that are free from flooding
  • In mid-May to early June, around the time that potatoes emerge and are actively growing, the first generation of adults emerges and begin to feed and mate on potato foliage
    • Eggs are laid in the soil
    • The first-generation larvae emerge and feed on tubers from early June to mid-July
  • In Alberta, under typical conditions, only one complete generation is observed, however a second generation can occur under warm conditions

Symptoms:

• Adult feeding results in “shot hole” damage on foliage
• Larvae burrow into tubers, feeding under the skin, resulting in a network of shallow tunnels
  • These tunnels appear as speckling or light brown spots when potatoes are peeled
  • The larvae are not present in tunnels
    • The discolouration is caused by the formation of wound healing tissues
  • While feeding does not reduce yields, it does cause cosmetic damage to tubers that may result in reduced marketability and down grading
    • Damage is more common in mid to late harvested crops
    • Damage may reduce the storability of the crop
    • Damage may tend to become more obvious as tubers are stored and begin to lose moisture

Monitoring:

• Monitoring for flea beetle adults is an essential step in their control
• Beetle populations tend to be higher closer to the field margins, due to the tendency of adults to overwinter adjacent to the fields, as well as the ability of adults to fly in from surrounding areas
• Plants should be monitored from the time that plants emerge until plants reach 30 cm (12 inches) in height
  • Early scouting involves the examination of the individual plants within groups of ten plants separated by about 40 metres), both along the crop at the edge of the field, as well as locations within the remainder of the field
  • Later scouting (for plants larger than 30 cm/12 inches) can be done with a sweep net at random locations throughout the field
• The threshold population would be 1 beetle per 60 inspected plants for early scouting and 1 beetle per 10 sweeps for later scouting

Management:

• Flea beetle populations can be reduced through regular crop rotations
  • Populations tend to build up with repeated cropping
• Separation from other fields and freedom from volunteer potatoes can also help to minimize levels
  • On a smaller scale, removal of plant residues may limit the ability of the flea beetles to overwinter and may reduce the pest population
• Earlier crops tend to be less affected than mid to late crops due to lower beetle populations
  • Damage symptoms may be reduced or less apparent in these earlier crops
• Applying registered chemical controls can be effective in reducing egg-laying adult populations and the subsequent numbers of emerging larvae
  • Spraying should be based on monitoring and economic threshold populations
  • Chemical controls are most effective when applied early in the season
  • Spraying to control the adults prior to egg-laying is the only option, as spraying to control larvae is not possible
  • The options for chemical controls in non-commercial plantings are limited