Clay’s question stirred me to do a search
the APHIS website implies that they are treating narcissus bulbs…..
T555—Treatment for Infestations of Ditylenchus dipsaci on Narcissus
T555-1 Narcissus (bulbs)
Pest: Bulb nematodes—Ditylenchus dipsaci
Treatment: T555-1 Presoak in water at 70 °F–80 °F for 2 hours, then at
110 °F–111 °F until all bulbs reach that temperature and
hold for 4 hours.