MARKET DISEASES OF FRUITS AND VEGETABLES 41 



the red color in the spots seems to be permanently lost. On some 

 other varieties the spots may become rather inconspicuous as the 

 natural coloring of the fruit develops. Evidence has been ob- 

 tained that the spots do not enlarge or change in any other way 

 while the fruit is in storage. 



Partial control may be obtained by spraying the trees in full 

 bloom with nicotine sulfate (40-percent nicotine) in the propor- 

 tion of 1 pint in 100 gallons of water. Enough soap should be 

 added to make the solution soapy to the touch, or casein spreader 

 should be used. The addition of nicotine to the calyx spray is 

 helpful also in controlling the thrips. 



(See 25.) 



Pear Leaf Blister Mite Injury 



(See Pears, Pear Leaf Blister Mite Injury, p. 60.) 



Phytophthora Rot 



(Phytophthora sp., probably P. cactorum (Leb. & Cohn) Schroet.) 



Phytophthora rot, a parasitic disease of apple and pear, has 

 been found on fruit grown in New York, Connecticut, Michigan, 

 Indiana, Washington, Oregon, and Idaho. So far as known it 

 does not cause heavy damage in any of these States, and it is not 

 common on the market. The rot can develop slowly at cold- 

 storage temperatures, but there is no evidence that it can spread 

 from affected to sound fruit either in transit or in storage. 



Phytophthora rot on apple, as seen from the outside, is light 

 brown (pi. 7 A) ; on pear it is dark brown to black. In both 

 apple and pear there is always a marked browning of the vascular 

 bundles, or strands that conduct food and water through the fruit. 

 This browning occurs in the large bundles near the core and the 

 smaller ones throughout the flesh ; from the former it may extend 

 even into the stem. In apple the flesh surrounding the bundles is 

 slightly browned; in pear it is browned scarcely at all. In some 

 varieties of pears, notably Clairgeau, the flesh is in fact decolor- 

 ized and has a clear, water-soaked appearance very much like 

 that of apple flesh affected with water core. 



The affected flesh of both apple and pear sometimes becomes 

 slightly spongy, but it is usually as firm as sound, healthy flesh; 

 unlike the decay produced by Rhizopus or blue mold, it rarely be- 

 comes soft and mushy. In cross section the area affected by Phy- 

 tophthora in both kinds of fruit has an indefinite boundary, so 

 that it is impossible to make a clear separation of diseased from 

 healthy flesh, as can easily be done in fruits attacked by Rhizopus 

 or blue mold. The affected flesh has no marked odor or taste. 



Phytophthora lives in the soil and the apples most likely to be 

 infected by it in the orchard are windfalls and fruits hanging low 

 on the trees. Apparently the fungus can penetrate the uninjured 

 skin of the fruit. On the market phytophthora rot has been found 

 in boxed apples and in shipments of low-grade pears. 



Phytophthora rot in marketed fruit can be reduced by elimi- 

 nating windfalls from the pack. 



(See 28, 65, 115, 18U.) 



