dust or wood chips under bins rather than al- 

 lowing them to touch the soil. Do not skid bins 

 on the orchard floor, load the bins roughly, or 

 allow drivers to speed through the orchard. 

 Urge pickers to handle fruit delicately to pre- 

 vent bruising. Finally, immediately take picked 

 fruit to the packinghouse where it can be cooled 

 rapidly. 



Control of Postharvest Disease 

 of Pears in the Packinghouse 



Control of postharvest diseases in the pack- 

 inghouse is based on spore load reduction 

 through sanitation and killing spores with frin- 

 gicides. Minimize damage to fruit by thorough 

 padding of surfaces and overall maintenance of 

 equipment. 



Controlling Spore Loctd in the 

 Dump Tank 



Pear packinghouses use either chlorine or 

 SOPP (sodium ortho-phenylphenate) in the 

 dump tank and flumes. Chlorine can do a very 

 effective job of killing spores in a dump tank if 

 the concentration of chlorine is correct, the 

 amount of dirt in the water is minimized, and 

 all areas of the fruit are penetrated. Chlorine, 

 however, lacks the ability to provide long-term 

 coverage of fruit in storage or on its way to 

 market and cannot penetrate wounds well. 



The concentration of spores in a dump tank 

 can be critical in terms of control of fungal dis- 

 eases in the packinghouse (Table 2). Several 



Table 2. The effect of dirt on the ability of 

 chlorine to kill fungal spores. 



Chlorine 



% Decay* 



ppm 



50 ppm (dirty water) 



50 ppm (tap water) 



100 



75 







♦Combination of Mucor, Botrytis and Penicillium 

 spores. 



organizations are available to monitor the num- 

 ber of spores in a dump tank. If monitoring is 

 used, 100 spores/ml should not provide a prob- 

 lem in a packinghouse; however, spore levels 

 over 300/ml should be avoided. 



The pH of a solution in which chlorine is used 

 will influence the amount of killing that chlo- 

 rine provides. Flotation salts dramatically raise 

 the pH to the alkaline area in most cases. Op- 

 erators are warned not to acidify or reduce the 

 pH or chlorine when used with sodium silicate, 

 since the flotation salt solution will form a gel 

 and solidify. Disposal of 3,000 gallons of "Jell- 

 O" can be a problem. 



Tests have been run on the fungicidal effects 

 of various flotation salts. Most of the flotation 

 salts have no fungicidal properties, that is, they 

 do not kill fungus spores. However, sodium 

 ligninsulfonate prevents germination of fungal 

 spores when used alone. When it was combined 

 with SOPP in the laboratory tests, no decay 

 spores germinated. Ligninsulfonate has a num- 

 ber of problems which must be considered. 

 First, SOPP measurements are difficult due to 

 the color of the solution. Second, fruit must be 

 thoroughly rinsed following treatment to avoid 

 injury. Operators should be aware that 

 ligninsulfonate and chlorine are not compatible 

 and should not be mixed. 



Heat Treatment of Dump Tanks 



Heat treatment of pear dump tanks is an- 

 other method of reducing spore load. Over the 

 past several years we have been experiment- 

 ing with heat sterilization of the dump 

 tank for those using SOPP in the sys- 

 tem. It appears that 130°F for 20 to 

 25 minutes kills spores in the dump 

 tank. 



The procedure is to lay a stjTofoam 

 cover over the tank at night after all 

 the fruit is out to turn on the boilers to 

 raise the temperature. In commercial 

 trials it took about 4 hours to bring the 

 tank up to the ISO^F level. The boil- 

 ers then were turned off and the 

 styrofoam was removed. By morning 

 the water was back to 70°F, so the fruit 

 could be run without injury. Water loss 



20 



Fruit Notes, Summer, 1995 



