Common potato insects: Scouting guidelines

Colorado potato beetle

Damaging stages

• Adult beetles
• Larvae

Sampling

• Sample 5 plants in 10 random sites per field. The 5 plants must be from different rows. Examine the whole plant before rows close.
• After row closure, examine 1 stem per plant.
• Record the number of adults and or larvae found in the 5 plants. An average of 4 egg masses per 50 plants is a potential problem.

Threshold

Notes

• Usually, early in the season the beetles are concentrated on border rows. Report the population in border rows separately, for example, there is an average of 3 beetles per plant in12 rows at the south border.

Potato flea beetle

Damaging stages

• Adults

Sampling

• Plant sampling same as above.
• Flea beetles jump quickly. Make observations as you approach the selected plants. Take care not to have your shadow fall on the plant before you can count the flea beetles. Flea beetle infestation is usually heavy when potatoes are grown close to crucifer crops.
• Damaged leaves have a shothole appearance. Record the number of plants with flea beetle damage.

Threshold

• Number of flea beetles per 50 plants/stems:
  • Adults: 20–25

Notes

• Flea beetles may be found in certain areas of the field. If infestation is heavy they can be found all over the field.

Potato leafhopper (PLH)

Damaging stages

• Adults
• Nymphs

Sampling

• Plant sampling same as above.
• Leafhoppers fly very quickly when disturbed. They are very tiny and may be difficult to see.
• Late detection of leafhoppers can cause serious economic losses due to hopperburn damage.

Threshold

• Number of PLH per 50 plants/stems:
  • Adults: 10–15 and/or
  • Nymphs: 25

Notes

• Do not confuse leafhopper nymphs with aphids. Leafhopper nymphs move fast and walk sideways.
• Aphids walk very slowly.

Aphids

Damaging stages

• Wingless forms
• Winged forms

Sampling

• Aphids are monitored at the same 10 sites selected for CPB scouting. At each site select 5 plants. Count all aphids found on one leaf per plant . The sample leaf should be from the mid section or lower half of the plant.
• Later in the season, as the lower leaves begin to senesce, sample 3 green leaves and 2 senescing leaves per site.
• Report the average number of aphids per leaf.

Threshold

Notes

• Aphids arrive in Ontario in July. The first aphid that colonizes the crop is the Potato Aphid which has very long legs.
• Wingless aphids move very slowly.

Tarnished plant bug (TPB)

Damaging stages

• Adults
• Nymphs

Sampling

• Plant sampling same as CPB monitoring. Adults fly quickly when disturbed. Make observations as you approach the selected sites. Nymphs walk fast on leaves. If you shake plants, nymphs drop to the ground.

Threshold

• Number of TPB in 50 plants/stems:
  • Adults: 15 and/or
  • Nymphs: 25

Notes

• Older nymphs are very robust and walk fast.

Cutworms

Damaging stages

• Larvae

Sampling

• Cutworms cut off the stems of small plants.

Threshold

• 3–5 moths trapped weekly in pheromone traps.

Notes

• The most damaging generation of cutworms develops in July/August.