due to heating was about 10% and SOPP loss 

 about 25%. 



We have done these trials with both silicate 

 and ligninsulfonate solutions. The tank con- 

 taining ligninsulfonate was reheated once 

 weekly for three to four weeks, during which 

 period of time it was not dumped and spore 

 count remained low. 



Thus, this method reduces the number of 

 times during the season that tanks must be 

 emptied. However, organic matter and other 

 debris eventually accumulate in the tanks and 

 the tanks require cleaning. 



Heating also will sterilize infected fruit at 

 the bottom of the tank. The calculated cost to 

 clean, empty and refill the tank was about $800, 

 while the cost to heat sterilize the tank was 

 about $200. Good ventilation of the packing- 

 house during heating is important. 



Direct Control of Decay Pathogens 



Spores of decay pathogens that survive 

 dump tank SOPP or chlorine treatments or 

 which contaminate the fruit after it leaves the 

 dump tank may be prevented from infecting by 

 application of a fungicide line spray. Commonly, 

 the benzimidazole fungicide thiabendazole 

 (TBZ) is applied but, unfortunately, not all 

 postharvest pathogens are controlled by this 

 fungicide. The following table lists common pear 



decay pathogens according to their 

 sensitivity to thiabendazole. 



Tank mixtures of TBZ + Captan 

 can improve control to a small extent 

 but do not significantly expand the 

 range of protection. However, the 

 use of Captan after harvest on pears 

 sprayed with oil during the summer 

 or wrapped in oil paper can develop 

 blotchy discoloration on the skin. 



In recent years concern has been 

 raised about the development of re- 

 sistance to benomyl in decay patho- 

 gens. Resistant strains have been 

 found in all major pear-growing districts. A close 

 examination of this potential problem has been 

 made in the Hood River district, where records 

 show the incidence of resistant strains has been 

 stable for the past several years. 



Postharvest Fungicides 

 for Decay Control 



Fungicides such as thiabendazole (TBZ) and 

 Captan are of tremendous importance in decay 

 control. The fungicides are often applied in a 

 line spray, after fruit crosses the sorting tables, 

 and often in combination with wax. Frequent 

 use of benomyl or thiabendazole in the orchard 

 has resulted in buildup of resistant strains of 

 Botrytis and Penicillium in many parts of the 

 world; thus, orchard use of these fungicides 

 should be avoided. Limiting benzimidazole fun- 

 gicides to packinghouse applications is critical 

 to preserve its effectiveness. Sanitation to pre- 

 vent increase and spread of resistant strains 

 isalso important. In addition, new fungicides 

 are being evaluated for their potential in con- 

 trolling postharvest pathogens. 



This article is reprinted with permission 

 from Washington State University Tree 

 Fruit Postharvest Journal, Vol. 6, No. 2. 



*sL» *sT> vL* *kL* vL* 

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Fruit Notes, Summer, 1995 



21 



