0524-2808-MTDC: Using a Steamroom To Sterilize Pallets of Styrofoam Seedling Container Blocks: Low-Humidity Heat Treatment

Another method subjected the styroblocks to hot, low-humidity (dry) air in an oven. If the oven was actually a large room, pallet loads of styroblocks could be left in the room long enough to sterilize them. The styroblocks would not need to be handled individually or loaded as they are with hot-water dipping, freeing workers for other tasks while the blocks were being treated.

Individual dry styroblocks were treated in an industrial oven (figure 3) for 10, 20, or 60 minutes at 170°F. Additionally, one set of styroblocks was wetted before the same treatments.

[photo] Styroblock sitting in industrial oven.

Figure 3—Styroblocks were baked in an industrial oven set to 170°F to
determine whether dry heat would sterilize them.

Subjecting the styroblocks to hot, low-humidity air for up to 60 minutes was ineffective (tables 2 and 3). Wetting the blocks improved the effectiveness, even when the blocks were heated for just 10 minutes.

Table 2—Test results for the industrial oven. Dry styroblocks were heated for 10, 20, and 60 minutes at 180°F
Fungus	PERCENT COLONIZATION
	10 min. dry		20 min. dry		60 min. dry
	Before	After	Before	After	Before	After
Fusarium	11	19	7	8	7	7
Cylindrocarpon	2	0	0	0	0	0
Trichoderma	28	36	42	46	37	33
Penicillium	23	19	28	13	27	18
Other fungi	66	65	55	53	63	51
No fungi	0	0	0	0	0	13

Table 3—Test results for the industrial oven. Wetted styroblocks were heated fro 10, 20, and 60 minutes at 180°F
Fungus	PERCENT COLONIZATION
	10 min. wet		20 min. wet		60 min. wet
	Before	After	Before	After	Before	After
Fusarium	17	0	4	4	13	0
Cylindrocarpon	0	0	0	0	0	0
Trichoderma	8	4	4	0	4	0
Penicillium	33	4	38	0	29	0
Other fungi	75	0	83	13	79	8
No fungi	0	88	0	88	0	92