The scientists were prompted into action by the destructive eating habits of the South American moth and Asian red palm weevil.
Larvae of the pests, including paysandisia archon, eat through fronds and bore into the wood. Both were thought to have come from palms imported in the 1990s.
But technical experts believe a microscopic ringworm could halt the invasion, which is said to have wiped out 80% of palms in one region.
The nematodes are sprayed onto the palms in a water-based liquid, according to Fredon, the regional pest-control federation.
"Some alarmists predict southern France will be bereft of palms within a few years," said a spokesman. "I’m optimistic and think we now have the means to protect them."