Preharvest Strategies to Reduce 

 Postharvest Pear Decay 



David Sugar 



Oregon State University Southern Oregon 



Research & Extension Center, Medford 



Robert Spotts 



Oregon State University Mid-Columbia Agricultural 



Research & Extension Center, Hood River 



Decay continues to be one of the most seri- 

 ous challenges facing the pome fruit industry. 

 It is apparent that both the condition of the fruit 

 delivered to the packinghouse and the quality 

 of care and treatment in postharvest handling 

 affect the risk of decay developing during stor- 

 age. Decay control begins in the orchard. Many 

 decay control practices can be performed 

 throughout the growing season and are ex- 

 tremely important if the grower is to obtain a 

 good packout and storage quality. Results of 

 research on a multifaceted approach to pear 

 decay control indicate that postharvest decay 

 is affected at every step of the production pro- 

 cess from orchard fertilizer application to stor- 

 age atmosphere. The following discussion con- 

 tains practical information that growers can use 

 to help control decay. 



Most fruit infections are caused by spores of 

 pathogenic fungi. All decay-causing fungi sur- 

 vive and multiply in the orchard and are found 

 in soil {Botrytis cinerea which causes gray mold, 

 Mucor piriformis which causes Mucor rot, 

 Phialophora malorum which causes side rot, 

 and several Penicillium species which cause 

 Blue Mold) or on the tree {Pezicula malicorticis 

 which causes bull's-eye rot). Many factors, in- 

 cluding soil temperature, moisture, and nutri- 

 ent availability, affect fungal populations. Most 

 fungal spores are in the top inch of soil or de- 

 bris in the orchard. These spores are extremely 

 small (about 1/2500 of an inch) and are spread 

 to the surface of fruit and to picking bins in and/ 

 or by rain and irrigation water, dirt and debris. 



and wind. 



Little can be done by growers to alter soil 

 moisture or temperature in a way that will re- 

 duce decay. However, orchard sanitation is a 

 key in decay control. Fruit left on the orchard 

 floor after harvest serves as a source of nutri- 

 tion for fungi. Populations of fungi that cause 

 decay are much greater in orchards that have 

 half a dozen pears on the ground under each 

 tree than in orchards that have only an occa- 

 sional fruit under the trees. The grower should 

 remember that ftniit on the ground does not get 

 sold and only feeds fungi that will rot more of 

 their ftoiit in storage. Thus, careful supervi- 

 sion of the picking crew is important to mini- 

 mize the amount of dropped as well as punc- 

 tured fruit. 



Several orchard conditions that affect 

 postharvest performance have been identified. 

 Fruit with high nitrogen (N) content is more 

 susceptible to decay (as well as to some other 

 fruit disorders) than ftniit with lower nitrogen 

 content. We have found that in pear trees which 

 need fertilizer, N applications approximately 

 one month before harvest minimize the amount 

 of fertilizer N in the fruit while providing ad- 

 equate nutrition for tree growth and the follow- 

 ing year's flower buds. Applications of fertil- 

 izer around bloom time resulted in relatively 

 high levels of fruit N at harvest. Fruit N may 

 also be lowered by reducing overall N availabil- 

 ity to the tree, reducing tree vigor, and promot- 

 ing dense and heavy cropping. 



Fruit high in calcium presents a lower risk 



14 



fruit Notes, Summer, 1995 



