Controlling tulip stem nematodes in tulip bulbs by a hot water treatment

A hot water treatment (HWT) protocol is needed to control tulip stem nematode (TSN) in tulip bulbs. A HWT above approximately 45°C in tulips is assumed to be harmful to the bulbs. Experience with HWT to destroy stem nematodes in daffodils shows that the required temperature for this is 4 hours at 47°C. The primary goal of this research was to determine the temperature tolerance of tulip bulbs, preferably in the range of 4 hours at 47°C. This was done by testing a number of combinations of pre-treatment temperature (PTT), HWT temperature and HWT duration. Bulbs that had been subjected to these treatments were planted in the field and the loss of bulbs and reduction in yield were monitored. A second goal of this research was to determine the combination of HWT duration and temperature at which TSN was totally eradicated. Trials were done with diseased (TSN) bulbs. The number of surviving nematodes were determined by using a 'fog chamber' technique. Two years of trials showed that tulip bulbs require high PTT's in order to survive HWT at higher temperatures. For example a HWT of 4 hours at 47°C preceded by pre-treatment of 1 week at 27, 30 or 33°C resulted in an average yield of 39, 64 and 92% (compared to the control treatment) respectively. The higher the PTT, the better the bulbs could tolerate the HWT. In the diseased bulbs we found total eradication of TSN at 4 hours 47°C, after a pre-treatment of 1 week at 30°C. Tulip bulbs were surprisingly tolerant of HWT at temperatures of 46 and 47°C, provided that bulbs receive a pre-treatment and HWT straight after lifting. Pre-treatment at 33°C gave the best result until now.