20 BULLETIN 1118, U. S. DEPARTMENT OF AGEICULTURE. 



losses. Under Florida conditions tlie normal temperatures occmring 

 throughout the growing months seem to be suitable for infection 

 and for the most part enough moisture is present to allow infection 

 of very susceptible species. Unless the host is in the proper stage 

 of development when there is an abundance of moistm'e, natural 

 infection does not occur; hence, for practical purposes, it is reason- 

 able to conclude that under average Florida conditions moisture 

 rather than temperature is the important limiting factor in natural 



infection, 



GROWTH HABITS OF GRAPEFRUIT. 



A brief consideration of the habits of growth of grapefruit trees luider 

 Florida conditions, together with an account of climatic conditions 

 occurring during the periods that a tree is susceptible to infection by 

 the scab fungus, will no doubt aid materially in establishing a 

 reasonable explanation of the behavior of the disease in nature. 



Bearing grapefruit trees in the neighborhood of Orlando, Fla,, 

 normally produce three distinct flushes of growth during the year. 

 The first growth comes out relatively slowly but uniformly over the 

 tree, usually during February, but in the southern part of Florida 

 it may be as early as January and considerably later at more northern 

 points. The emerging of blossom buds may be the first signs of 

 growth, or vegetative growth and blossom buds may come out 

 simultaneously, or vegetative flushes may partially harden and then 

 develop blossoms on this new wood (PL I, Fig. 1). 



If the weather is warm and conducive to the active growth of 

 citrus trees there is a comparatively short time between the first 

 signs of growth and the falling of petals from the latest blossoms, 

 but if the weather is cold, rainy, and otherwise unfavorable for 

 growth the vegetative parts emerge very slowly, and the blossoming 

 period alone may extend over more than six weeks. Usually the 

 greater part of the crop develops from this spring bloom. 



The second flush comes out very rapidly, usually during the hot 

 dry weather of May several weeks in advance of the rainy season, 

 and in a few days the leaves reach a width of an inch or more. This 

 flush is much less evenly distributed over the tree and is rather 

 irregular in beginning growth. There occurs at this time or some- 

 what later a small quantity of bloom from which develops the June 

 bloom fruit, which is quite inferior in quality. The so-called ''June 

 bloom" is relatively insignificant in quantity. It occurs practically 

 only on trees with little or no fruit resulting from the spring bloom, 

 or following a drought, or on trees which have some root or trunk 

 disease. 



The third flush usually starts growing in September, well after the 

 rainy season has passed. The quantity and character of growth is 

 essentially the same as that occurring in May, but seldom accom- 



