moist weather. Botrytis spores are formed in 

 clusters and can become airborne. Millions of 

 very small spores can form in a short time. In 

 addition to causing stem enddecay and the in- 

 fection arising in wounds, Botrytis rot has the 

 ability to move from finiit to fruit during the 

 storage season. It can spread over time from 

 infected fruit to surrounding healthy fruit and 

 form a cluster or nest of decay. Hence, this dis- 

 ease has been called nest- 

 rot. 



Blue Mold (Penicillium expansum) 



Blue Mold caused hy Penicillium expansum 

 is a common and destructive rot found on fruits 

 in storage and at the market. Blue Mold spores, 

 like Gray Mold, can be airborne in tremendous 

 numbers. 



Stem and neck rot develops from stem in- 

 fections in fleshy stemmed varieties such as 

 Anjou and Comice. Losses from this disease 

 have increased since use of polyethylene box lin- 

 ers has extended the storage season for pears. 

 The amount of decay that develops on a single 

 fruit depends upon the length of the storage 

 period. It may involve only the stem, the stem 

 and a small area at its base, or the entire upper 

 half of the fruit. High humidity within the poly- 

 ethylene box liner favors the development of the 

 white to bluish-green fungal mass of spores on 

 the surface of infected tissue. 



Pinhole rot occurs mainly on Winter Nelis, 

 a pear variety with large, prominent lenticels. 

 It first appears as numerous minute spots of 

 decay scattered over the surface of the fruit; 

 infection apparently occurs at the lenticel. As 

 the disease progresses, the spots increase in size 

 and finally coalesce, and the entire fruit decom- 

 poses. 



Blue Mold is generally considered a wound 

 parasite, but it can penetrate through lenticels, 

 particularly those near bruises. Late in the stor- 

 age season when fi-uit has become weakened 

 by ripening and aging, most varieties are sus- 

 ceptible to lenticel infection by Blue Mold. This 

 type of infection may result when rotted pears 

 are handled carelessly during repacking. En- 

 vironmental conditions such as moisture, ven- 



tilation and temperature directly influence the 

 development of decay. The atmospheric mois- 

 ture necessary to prevent pears from shrivel- 

 ing is sufficient for Blue Mold development. 

 Lack of ventilation due to tight packing and lack 

 of air space in storage increases the moisture 

 around the fi-uit and slows the rate of cooling, 

 making conditions favorable for fungus devel- 

 opment. 



Fungus diseases develop more rapidly at 

 temperatures higher than the usual storage 

 temperature for pears. Pears that are delayed 

 going into storage, cooled slowly in storage, 

 stored till late in the season, or held at warm 

 temperatures after removal from storage are 

 particularly subject to infection. Disease is not 

 necessarily prevented or arrested even at 30° 

 to 32°F. Rotten spots continue to enlarge, and 

 even new infections can be initiated at these 

 temperatures. Decay proceeds slowly in the 

 early part of the storage season when fi-uit is 

 firm and somewhat resistant, but during long 

 periods of storage it can cause serious losses. 



Coprinus Rot 



Another fungal disease is Coprinus rot, 

 which is often mistaken for bull's-eye rot. 

 Coprinus rot has appeared in both Hood River 

 and Wenatchee. This low temperature organ- 

 ism (mushroom fungus) will nest and spread 

 like Gray Mold. Spores come from a mushroom 

 in the orchard and appear to infect fruit during 

 the last month before harvest. One major dif- 

 ference between Coprinus rot and bull's-eye rot 

 is the presence, in cold storage, of a cobweb- 

 like, white fungal growth on the fi-uit surface 

 in Coprinus rot. 



Mucor Rot 



Mucor is a soil-borne fungus that grows well 

 even during the winter It is found in varying 

 amounts from orchard to orchard and varies in 

 quantity depending upon the time of year. For 

 example, immediately after harvest the spore 

 count in orchard soil increases. The Mucor fun- 

 gus is found in debris and litter on the soil sur- 

 face and most occur in the top two inches of soil. 



Fruit Notes, Summer, 1995 



17 



