Parks and green spaces

Controlling the oak processionary using nematodes

Figure 1: Oak processionary caterpillars

Figure 1: Oak processionary caterpillars

Oak processionary caterpillars, Thaumetopoea processionea, pose a health risk as their stinging hairs can cause skin irritation and even trigger serious allergic reactions in people. Therefore, they must be regularly controlled in public spaces. This must be done prior to the formation of stinging hairs, in other words before the third instar. Nematodes are an environmentally friendly alternative to established control methods as they are effective on caterpillar fauna after just a few hours.


Tp-Nema® contains Steinernema feltiae nematodes and a hydrating gel, which is also used in foodstuffs. The gel enables the nematodes to survive on the caterpillars for up to three hours and enter them. Tp-Nema® can be used as soon as the caterpillars have hatched. At this time of year, the trees will still have no leaves on them yet. Spraying up to and including the third instar is possible (approximately up to the end of May). For maximum effect, treatment should be carried out again within two weeks.


Figure 2: Applying Tp-nema® using a spray cannon

Figure 2: Applying Tp-Nema® using a spray cannon, Photo: Henry Kuppen, Terra Nostra

The caterpillars must be active on the tree and as many of them sprayed as possible. Therefore, and because of the risk of drying out, apply the nematodes in the evening and night between 20:00 and 06:00. This window can vary depending on the weather.

Use a spray cannon to apply the nematodes. Before using for the first time, check that all openings are large enough and that the nematodes can pass through the nozzles unharmed. Use approx. 10 litres of water per tree.