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Oak processionary, treatment for this caterpillar

Oak processionary caterpillars writhing across oak tree bark in droves.

This well-known oak tree parasite is a caterpillar that devours leaves.  It then gathers into a nest that looks like a spider web.

The scientific name is Thaumetopoea processionea and it’s also called oak processionary moth.

Solution to treat against oak processionary

For a long time, there was practically no available effective treatment. The only solution was to prevent caterpillars from spreading to other oak trees.

  • Traps across the trunk can catch colonies as they climb up, but they must be frequently monitored and emptied.
  • Locate and destroy nests which are a wispy white color, as if made from spider webs.
  • In some areas such as England, authorities prefer that you report the nests to the local forestry bureau. They will dispatch a team to rid you of the nest.

To preserve and protect surrounding trees, cut off branches where nests form and destroy them.

Biological control is turning out to be quite effective, especially when several treatments are applied. They target the caterpillars at a specific stage, so it’s crucial to get the timing right.

  • Right after hatching, spraying a nematode called Steinernema feltiae resulted in a 95% reduction the pest.
  • When caterpillars start feeding on leaves, it’s possible to use Bacillus thuringiensis against them.
  • At nesting stage (where they become moths), mechanical removal is preferable, as described above.
  • Finally, it’s possible to trap the moths themselves with well-placed pheromone traps. These stay effective for a month and a half.

→ Also read our page on caterpillar control

Smart tip about oak processionary

Oak processionary caterpillarTake great care when cutting caterpillar-infested branches off. Indeed, hairs from these hairy caterpillars are extremely itchy, not only for you but also for dogs, cats, and any other pet living in your house!



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Images: 123RF: Hilda Weges, CC BY 2.0: Andreas März; Pixabay: Jacqueline
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