ilO KXPERIMENTAL FARMS. 



seriously the question of remedies, making it necessary to apply several successive treat- 

 ments, if it is hoped to thoroughly free a plant infested by this enemy so difficult to 

 •conquer. 



The mere fact of a scale-insect occurring, even in vast numbers, upon a given p'ant 

 •does not necessaril}' prove that the species is a dangerous enemy to that kind of plant ; 

 for, although it may possibly be so and should be regarded with suspicion, this habit of 

 •occurring in great numbers on isolated trees, but on no others surrounding these, has 

 frequently been noticed with scale-insects, and is probably due to some lack of vigour in 

 the individual tree. In the case of the San Jose Scale, on the other hand, if other trees 

 are reasonably near, it is almost certain that they will soon become infested ; and, when a 

 severe case of infestation is found, one of the first things looked for when considering 

 whether the pest is actually the San Jose Scale or one of the other species which super- 

 ficially resemble it very closely, is, whether surrounding trees are also infested. 



This important difference of habit in spreading and the much more fatal efiects 

 upon trees from the presence of the San Jose Scale, make much more stringent measures 

 necessary to secure its eradication than with many other species, even frequently render- 

 ing it advisable or imperative to destroy many trees, if not whole orchards. This being 

 the case, the very great advantage is obvious of being perfectly sure as to the identity 

 of an infesting scale-insect before valuable trees are condemned to destruction. 



Unfortunately, as stated, there are several species of scale-insects which bear a 

 very close superficial resemblance to the much to be dreaded San Jose Scale. On this 

 point, which has been referred to by many entomologists, Mr. T. D. A Cockerell, a 

 iiigh authority, may be cited : " It has been a matter for dispute whether the San Jose 

 Scale can be certainly recognized in the field. Its efiect on the tree, killing the branches, 

 is characteristic, but hardly in any sense diagnostic, while the reddening of the tissues 

 of the plant adjacent to the scale is sometimes well marked with A. ancylus, as well as 

 with perniciosus. A little experience, however, enables one to recognize the ashy gray, 

 generally thickly massed scales of perniciosus, with the dot and ring of the male scale, 

 as against the dark scale and contrasting reddish orange exuvite of ancylus, or the 

 similar scales of ostrecpjormis and Forbesi. At the same time, it is to be recommended 

 that the diagnosis made in the field be in every case confirmed by examination of the 

 insect under the compound microscope if either locality or plant is new." {Technical 

 Series, Bull. 6, U. S. Div. o/ EnL, J897.) 



The above is from a valuable pampiilet prepared under Dr. Howard's direction for 

 the special purpose of helping students to distinguish between these different scale- 

 insects. Prof. F. M. Webster says : " I know of no insect the detection of which has 

 given expert entomologists more trouble than this one. Its extreme minuteness, its 

 close resemblance to the other species less harmful, and the frequency with which it is 

 found concealed in cavities and about the wrinkles of the bark or under buds, render 

 its detection, when present in limited numbers, a matter of extreme difficulty." [Ohio 

 Bulletin 81, p. 183.^ 



For the exact separation of these closely allied species it is necessary to take the 

 females fiom beneath the scales and examine them under a microscope after special 

 preparation. The differences are then readily seen, but these are beyond the power of 

 ordinary pocket lenses or magnifying glasses, and require compound microscopes, which 

 are expensive instruments not in the hands of ordinary fruit growers, and for the use of 

 which special knowledge is needed. 



As, therefore, there are several kinds of scale-insects resembling each other so 

 closely at first sight as to make it necessary for even expert entomologists to examine 

 them with a microscope before being positive as to the identity, and as one of these, to 

 wit the San Jose Scale, is extremely injurious and the others not nearly so much 

 so, we invite all fruit growers to send for examination and report specimens of any 

 suspicious scale-insects which they may find upon their trees befoi-e they adopt extreme 

 measures or even decide upon what measures they will take to free their orchards. Not 

 only does the San Jos^ Scale spread more rapidly than many other species, but it has 

 been found much more resistant than others, to the ordinary applications used for scale- 

 insects. 



