CALIFORNIA AVOCADO ASSOCIATION 



77 



or amber-brown, and are circular or slightly elongated. They are about the 

 size of the red scale which attacks citrus. The scales are slightly convex, the 

 central nipple is grayish, surrounded by a dark depressed area. It is scientifically 

 known as Chrysomphalus dicl^ospermi, Morgan. 



The section where this scale is especially destructive to the avocado is on 

 the keys and stretches of land lying between the ocean and bay inlets along the 

 coasts of Florida. The writer has found that the temperature runs more evenly, 

 and averages a number of degrees warm)er throughout the year in these localities 

 than on the mainland, which perhaps accounts for the abundance of the scale in 

 those places. It is, however, doing damage, and is to be found in varying num- 

 bers in nearly every place where the avocado is growing in southern Florida. The 

 scale is a pest in avocado nurseries and especially finds protection where the trees 

 are crowded together. It has been found by the writer to infest both the West 

 Indian and Guatemalan varieties. It is known to attack various plants in tropical 

 and semi-tropical countries. 



Where this scale attacks the avocado it makes inroads into the tree, attack- 

 ing the twigs and branches. The branches so attacked are gradually weakened 

 and ultimately become of little use to the tree. Where this scale is present in 

 numbers, the branches infested soon become roughened and crack considerably, 

 affording entrance places for various fungus and bacterial diseases. Branches 

 severely attacked generally show a lack of lateral twigs and foliage. This scale 

 does not produce honey dew as is characteristic of some scale insects. It does 

 not attack the fruit but confines its attacks to the branches, twigs, and leaves. 



A thrips which often attacks the avocado in the open in Florida is the 

 greenhouse thrips of the northern states scientifically known as Heliothrips hem- 

 orrhoidalis B. It possesses a black head and a thorax with the abdomen yellowish 

 brown in color, and in size is similar to most thrips. It attacks the foliage and 

 when very numerous may also attack the fruit. It is present on the avocado during 

 the dry winter months, and evidently the rainy weather of summer is unfavorable 

 to its multiplication. They work very rapidly on the foliage, and the writer has 

 observed trees which were completely defoliated in a comparatively short time. 

 The work of the thrips is easily distinguished from that of the red spider. In 

 addition to the foliage appearing brown, it also possesses a roughened surface 

 due to the feeding of the thrips. It confines its attacks, almost entirely, to the 

 upper surface of the foliage. 



Like citrus, the avocado also possesses its particular white fly in Florida. 

 It is scientifically known as Trialeurodes floridertsis Q. This fly is very small 

 in size, somewhat smaller than those which attack citrus. In color it is golden 

 brown, abdomen with large orange colored areas, and wings white. This fly 

 may also be distinguished from a number of other white flies in that the pupae 

 possess a characteristic fringe. It is present in nearly every locality where 

 avocados are growing in Florida, but evidently is sensitive to varying changes of 

 temperature as regards its activities and numbers in different localities. It prefers 

 localities where the trees are protected and the temperature runs more evenly. The 

 work of this white fly is similar to white flies which attack citrus, in that it attacks 

 the foliage and produces an abundance of honey dew in which sooty mold develops 

 on the leaves, fruit and branches. It is a pest in the nursery as well as in the 

 bearing grove. 



Another pest of importance is the avocado red spider. On the approach of 

 dry weather in the fall this spider becomes very active, and often gives considerable 

 concern to the grower. Especially is this true where trees are more or less neg- 



