34 MISC. PUBLICATION 4 98, U. S. DEPT. OF AGRICULTURE 



Thrips marks on California fruit may be fairly smooth, affecting 

 the shape and texture only slightly, but in severe cases they may affect 

 both the shape and the texture severely. 



The adult citrus thrips (Scirtothrips citri) averages less than a 

 twenty-fifth of an inch in length and is pale orange yellow; hence it 

 is not easy to see. It overwinters in the egg stage, and several broods 

 may be produced during the summer. There are no striking differ- 

 ences between the effects produced by citrus thrips and those produced 

 by the Florida flower thrips (FrankUwdeUa bispmosa). 



(See 94, 100, 131, 132.) 



TRICHODERMA ROT 



(Trichoderma viride Pers. ex Fr. 8 ) 



Trichoderma rot is seen occasionally on oranges and lemons from 

 storage. It has been reported in the United States, Italy, South 

 Africa, and Southern Rhodesia. The decay at first affects only the 

 rind, causing it to turn light brown although it remains firm. It later 

 turns the rind dark grayish brown and spreads into the interior of 

 the fruit causing it to become soft and spongy. Decayed tissue has a 

 definite coconutlike odor. Clumps of white mycelium form on the 

 larger decayed areas, and these produce cushions of powdery green 

 spore masses. Because of this color the decay may be confused with 

 blue mold rot (p. 19). It is, however, much firmer than blue mold 

 rot, develops more slowly, and bears fewer spores on its surface. 



The causal fungus, Trichoderma viride, is usually considered a soil- 

 inhabiting saprophyte. It has been reported as a parasite on other 

 soil fungi. Apparently it usually enters the fruit through injuries 

 in the rind; so control measures used for blue mold rot (p. 21) should 

 also prevent trichoderma rot. 



(See 48, 43, 50, 91.) 



WATER SPOT 



Water spot is a disease that develops in California on mature Wash- 

 ington Navel oranges on the tree, following exposure to 2 or 3 weeks 

 of rainy or foggy weather. In its earliest stage it occurs as a minute 

 cracking of the cuticle, usually near the navel, caused by a swelling of 

 the underlying tissue when it absorbs water (pi. 10, B). It also de- 

 velops on the shoulder of the fruit, where drops of water may easily 

 collect, and at or near wounds. If the wet weather continues these 

 affected areas enlarge, assume a water-soaked appearance, and are 

 eventually invaded by decay organisms, chiefly green mold or blue 

 mold (pi. 10, G). Under extreme conditions half or more of the fruit 

 on a tree may be ruined by this rind break-down and the rot "that 

 follows (pi. 10, D). Water spots that develop elsewhere than at 

 the navel usually start at bruises or skin breaks. 



If the weather turns dry after the first stage of the spots has de- 

 veloped, the water-soaked areas become brown, dry, and slightly 

 sunken, and active decay of the fruit is prevented. However, some 

 of the blemished fruit may escape notice during the harvesting and 

 packing operations and so get into the packed boxes. It may also 

 happen that the spots are invaded by fungi but are kept from decaying 



8 Perfect stage, Hypocrea rufa Fr. 



