12 MISC. PUBLICATION 49 8, IT. S. DEPT. OF AGRICULTURE 



BROWN ROT 



(Phytophthora citrophthora (Sm. and Sm. ) Leon. P. parasitica Dast., P. palmivora 

 Butl., P. syringae Kleb., and P. cactorum (Leb. and Conn) Schroet.) 



Brown rot is found on lemons in groves, packing houses, and in 

 storage, and it occurs in all the principal citrus-growing countries of 

 the world. The rot is first evident as a slight discoloration of the rind 

 and in mature lemons the affected tissue soon takes on various shades 

 of drab and brown (pi. 8, D). The juice of the lemon is too acid 

 for the organism so that the growth is likely to be confined to the 

 rind, the central cylinder, and the division tissues between the seg- 

 ments of the flesh. The fruit does not soften rapidly. There is 

 usually no evidence of mold on the surface, but under very humid 

 conditions a delicate, white surface mold appears. The disease can 

 be identified by the rather penetrating, aromatic, rancid odor of 

 affected tissues. 



The causal fungi live in the soil and much of the infection that they 

 produce in the orchard results from the splashing of their motile 

 swimming spores onto leaves and fruit during rains. If winds ac- 

 company or follow immediately after the rain, the spores may be 

 carried high into the tree and cause infection 20 or 30 feet from the 

 ground. Infected fruit may carry spores into the washing tank and 

 thus result in a development of the disease later in storage. 



As a preventive of infection in the packing house copper sulfate 

 or potassium permanganate is sometimes added to the wash water at 

 the rate of V/ 2 pounds to 1,000 gallons. Sodium carbonate and tri- 

 sodium phosphate have been found effective when used in 114 -percent 

 solutions. A 5- to 7-percent solution of borax has not been found so 

 satisfactory unless the water is heated. The treatment most commonly 

 used at present for the control of this rot consists in' submerging 

 the fruit for 2 minutes in water heated to 115° F. or for 1 minute in 

 water heated to 120°. Although the different species of Phytophthora 

 do not have exactly the same temperature response they are all greatly 

 delayed in growth and rotting effect at a temperature of 50°. 



(See 11, 1&, lt3,Jfi,108.) 



COTTONY ROT 

 (Scleroti?iia sclerotiorum (Lib.) DBy.) 



Cottony rot, caused by the fungus Sclerotlnia sclerotiorum, is widely 

 distributed in many of the citrus-growing regions of the world. It is 

 found chiefly in lemons. 



Affected fruit softens slowly, and the skin is at first leathery and 

 pliable. In a dry atmosphere the color of the decayed area on a 

 mature lemon becomes yellowish brown or greenish brown. In a 

 moist atmosphere the fruit is rapidly covered with a white, cottony 

 growth of mycelium that gives the outstanding distinguishing char- 

 acteristic of the decay (pi. 9) . Cheesy, black sclerotial bodies are later 

 developed in the fungus mat. 



Cottony rot is a rapidly spreading contact decay that may attack 

 both green and mature fruit and cause heavy losses in the packing 

 house or in storage. Moderate temperatures, high humidity, and 

 stagnant air are favorable to its development. However, the causal 



