From the 1930s, formaldehyde was included in the hot water to kill nematodes more quickly and reduce Fusarium basal rot fungus transmission between bulbs during the dipping process. Approval for the use of formaldehyde in HWT for bulbs ended in December 2008, so HDC project BOF 61a was commissioned to investigate alternative chemicals or modifications to the HWT regime.
In the first part of the project, a range of chemicals and HWT regimes varying from the standard one, with either modified temperatures or durations, were tested.
Treatments identified in the first 18 months of the project that were effective at controlling stem nematode and/or basal rot, and which did not appear to have severe phytotoxic effects, are now being tested on a larger scale in field trials.
If a successful treatment is identified, further development will almost certainly be necessary before any chemical component can be approved for use in HWT. It is therefore likely that there will be no formaldehyde replacement available before 2011.
In the meantime, the project shows that exposure to HWT at 44.4°C for three hours is sufficient to control stem nematodes that are in the "wool" form at the beginning of the treatment, with no requirement for additives to enhance the level of control.
Where basal rot is a concern, thiabendazole (Storite Clear Liquid) should be used in the HWT tank or as a cold dip (see the label) until approval expires at the end of 2011.
For details on all activities, visit Horticultural Development Company.