Postharvest Apple Rots: Dr. Rosenberger's Approach 



Daniel R. Cooley 



Department of Plant Pathology, University of Massachusetts 



Dr. David Rosenberger of the Hudson Valley Lab, 

 Cornell University, has been studying postharvest rots on 

 apples for a number of years. In a recent talk at the 

 University of Massachusetts he discussed some of the key 

 points in the management of these problems, and these 

 points will be outlined in this article. Dr. Rosenberger 

 emphasized that the key to good management was an 

 integration of several techniques: 



* Appropriate and sufficient summer fungicide applica- 

 tions; 



* Good management of the harvesting process; 



* Appropriate postharvest chemical use in the dip tank; 



* Good sanitation in the storage facility and harvest proc- 

 ess; and 



* Intelligent use of storage and marketing options. 



Fungicide Applications During the Growing 

 Season 



Good storage rot control begins in the field before 

 harvest. For example, last summer the wet harvest tem- 

 peratures, combined with a tendency to leave fruit on the 

 tree for color development, produced a larger than normal 

 amount of rot in storage. This situation occurred because 

 the wet weather during summer and harvest increased the 

 rot inoculum and unseen fruit infections. 



There are a number of diseases, rots and others, which 

 can develop in storage: 



Pin-point scab can be a problem. Late-season scab 

 infections on the fruit can go undetected, and develop in 

 storage into visible lesions. The best way to avoid a 

 problem is to maintain good scab management throughout 

 the season. 



Sooty blotch and fly speck are late season problems that 

 may develop if summer weather conditions are humid. 

 Interestingly, the fungi which cause these diseases will not 

 grow at storage temperatures. However, unseen infections 

 on harvested fruit can develop in storage. The fungi grow 

 duringthe period when the fruit is cooling, before it reaches 

 the storage temperature. In a large storage room, where it 

 may take several days to reach the desired temperature, the 

 fungi grow well for a time. Rapid cooling after harvest 

 would help eliminate this problem. 



Moldy core is another disease which develops in the 

 field, and lies undetected until the fruit has been in storage. 

 Moldy core can be caused by a number of fungi, but about 

 90% of the problems are caused by Altemaria. The 

 infections occur during bloom and petal fall. Unfortu- 



nately, there do not seem to be any fungicides which control 

 the disease very well. The infections develop inside the 

 fruit, largely protected from fungicides. 



Fungicides can help reduce many of the other posthar- 

 vest rots. A minimum program of 1 appUcation in early July 

 and 1 again in early August should be adequate to control 

 development of most of the late season fungal infections. 



Management During Harvest and Packing 



Wounded or over-mature fruit are more susceptible to 

 postharvest diseases. For example, a rough orchard road 

 can lead to significant quantities of wounding, which will 

 increase the fruit's susceptibility to rot. Taking the time to 

 smooth the orchard floor can reduce this problem. Avoid 

 storing over-mature fruit. Ingeneral, the most mature fruit 

 should be marketed first, and the less mature stored. 



As mentioned above, rapid cooling can decrease the 

 time that rot fungi have to develop. In some cases, it will 

 stop development completely, while in others it will slow 

 the process. Rapid cooling slows down fruit ripening, 

 which slows down all forms of fruit rotting since fruit lose 

 their resistance to fungi as they ripen. 



Another management practice which affects posthar- 

 vest rots as well as storability is calcium nutrition. Low 

 calcium in the fruit increases its susceptibility to rot organ- 

 isms. Perhaps other nutrients, such as potassium also can 

 affect rot susceptibility. Maintaining a calcium nutrition 

 program is advisable. 



Sanitation 



Attention to sanitation can be beneficial at all points in 

 the postharvest handling process. The basic aim is to keep 

 the inoculum for postharvest rots away from the fruit. 



Old bins can contain bits of old, rotten fruit from the 

 previous year. Designating a single bin for culls can reduce 

 the spread of this inoculum. Soaking a bin with bleach 

 solution (10% in water) mixed with either detergent or a 

 standard spreader-sticker, and allowing the bin to air dry 

 also will reduce problems. 



Dirt from the orchard fioor also can carry inoculum. 

 To counter this problem, keep bins on sod and away from 

 direct soil contact. Do not operate equipment so that it will 

 dig up soil when a bin is Ufted. In wet weather, rigging a 

 hose to wash trucks, trailers, and bins wiU reduce the 

 amount of soil which is carried into the drench solution. 



Reducing the inoculum load in the drench solution is 

 very important, since it comes in contact with virtually all 



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