526 INSECTS AFFECTING VEGETATION 



injury. The application of a spray in the fall may be attended by 

 a falling of the fruit if the tree is in a weakened condition from 

 disease or unfavorable growth conditions. 



There is no method of treatment for chemical injuries to the 

 fruit after they have occurred. If the injury is due to feeding too 

 much of readily soluble fertilizers, further application of these should 

 be avoided until the tree recovers. Chemical injury due to overfeed- 

 ing most commonly follows a heavy application of a readily soluble 

 fertilizer followed by a heavy rain ; or where too large a quantity of 

 copper sulphate has been applied to the soil or placed beneath the 

 bark to attempt the cure of dieback in the trees. Sprays should be 

 mixed carefully, and applied according to directions. 



Nail-Head Rust or Scaly Bark Spots. The spots on fruit that 

 accompany the Florida scaly bark (also known as nail-head rust) 

 are hard, circular, sunken, more or less corky spots, causing prema- 

 ture coloring and dropping of fruit. The spots are at first yellowish 

 to reddish-brown on green fruit, and finally become dark and sunken. 

 In ringed spots the rings first become sunken with a higher part in- 

 side. This central part afterwards sinks in, and the whole area in- 

 side the ring is involved. The spots vary in breadth from one-fifth 

 to one-half inch. These spots are found only on sweet oranges. They 

 are not known to occur on grapefruit or tangerines. Some of the 

 spots are quite similar to anthracnose, or to some spots produced by 

 chemical injuries; but they may be distinguished (1) by some of the 

 spots starting as sunken rings, (2) by grapefruits or citrus fruits 

 other than sweet oranges not being affected even when exposed to 

 infection. 



The method of treatment for this disease will vary according to 

 the severity of the disease and the attitude of the grower toward his 

 grove, whether he be aiming for temporary results or be willing to 

 sacrifice present profits for future benefits. The various lines of 

 treatment found by experiment to be successful in controlling the 

 trouble may be summed up as follows : 



1. Top- working to grapefruit or other resistant varieties. 



2. Heading back and spraying with Bordeaux, followed by an 

 insecticide. 



3. Heading back and painting with carbolineum (half 

 strength). 



4. Pruning out dead wood. 



5. Spraying the fruit with fungicides, followed by insecticides. 

 (Fla. E. S. B. 108.) 



Scab. This disease, which is especially common on sour or- 

 anges and lemons, makes its appearance on the fruit as irregular 

 light brown or corky projections from the surface. It is caused by a 

 fungus which attacks the fruit or leaves when quite young. Its at- 

 tack on sour oranges and lemons (and sometimes on Satsumas and 

 grapefruit) often results in making them misshapen and unsightly. 

 In severe attacks, projections of a dark gray to corky or even tan 

 color will be seen extending out from the surface. The surface of 

 the fruit between the warts is usually of a normal color. Often these 



