he terminal filter. The unit, when used with a commercial drencher and the 1.0 gm terminal filter, removed only 3% of P. expansum conidia. The 1.0 µm filter is nominally rated, and pore size varies considerably.
The cartridge filter system with the 0.45 µm terminal filter effectively removed spores in both laboratory and commercial tests, reducing the spore level by 92% to 99%. However, if this system is to become more useful for spore removal and decay control in packinghouse drenchers, dump tanks, and flumes, the capacity must be increased well beyond the current 10 gal./min. rate. In addition, terminal filters of 1.0 µm remove about 20% and 0.45 µm filters an even greater but unknown amount of thiabendazole, the most common fungicide used in drencher water for decay control, and fungicide concentration must be monitored and adjusted continually.
As with the sand filters, the cartridge filter units effectively increase the time that drencher suspensions can be used. Because drencher water may contain DPA, calcium chloride, and thiabendazole, reducing the amount of waste water generated (and which must be disposed of) is a positive benefit of filtration. During harvest, bottoms of bins often are covered with soil and debris.3 Filter life, and possibly filtration rate, may be increased by improved bin sanitation.
We thank the Winter Pear Control Committee for partial funding of this research. Use of trade names in this article does not imply endorsement of the products named or criticism of similar products not mentioned by Oregon State University.
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Robert A. Spotts and L. A. Cervantes
Mid-Columbia Agricultural Research and Extension Center, Oregon State University, Hood River
Tree Fruit Postharvest Journal 4(1):16-18