igii 



APPLE TWIG BORER 

 a, Beetle, dorsal view; a, Side view; b, Pupa, from 

 beneath; c. Grub, side view; d, Apple twig showing 

 burrow; e, Burrow in tamerisk with pupa at bottom; 

 f. Stem of grape, showing burrow. All enlarged 

 except stems showing burrows. 



duced from the middle of summer on. 

 These spores are capable of withstanding 

 freezing and drying, but they are evi- 

 dently of very little importance in start- 

 ing the following year's infections in this 

 locality, for the fungus very frequently 

 infests a twig so thoroughly that it gets 

 into the buds, and in the dormant buds 

 it winters over in the mycelial form, and 

 is there ready to expand and keep pace 

 with the growth of the new leaves as 

 they develop the following spring. This 

 wintering-o^ er of the fungus in the buds 

 is a rare and peculiar habit for the mem- 

 bers of the mildew group of fungi. It is 

 made possible no doubt by the mild win- 

 ters, and is responsible for starting prac- 

 tically all the infections in the spring. 



The disease appears to have existed 

 here for the past fifteen or twenty years, 

 and for a number of years now has been 

 attracting the attention of the growers. 

 It early developed that the methods 

 ordinarih- recommended for apple mil- 

 dew control are inef¥ectual in this sec- 

 tion. About four years ago Mr. C. H. 

 Rodgers took steps to interest the United 

 States Department of Agriculture in 

 investigating the problem. It was impos- 

 sible to take the work up until a year 

 ago last spring, and in the meantime Mr. 

 Volck was at work, and obtained some 

 very valuable results. During the pres- 



OYSTER SHELL BARK LOUSE 



a, Female scale, from below, showing eggs, greatly 

 enlarged; h. Same, from above; c. Female scale on 

 twig, natural size; d. Male scale, enlarged. 



BETTER FRUIT 



ent season Mr. Volck and the federal 

 department have been co-operating, and 

 a considerable amount of data has been 

 gathered, which is to be published this 

 year as a bulletin of the United States 

 Department of Agriculture. 



The various fungicides commonly in 

 use for controlling plant diseases may 

 be placed under two headings — the cop- 

 per sprays and the sulphur sprays. The 

 copper sprays include bordeaux as ordi- 

 narily prepared, and, in addition, various 

 modified bordeaux, copper acetate, cop- 

 per chloride, copper carbonate, etc.; and 

 the sulphur sprays have until recently 

 consisted of either ordinary ground sul- 

 phur or one of the soluble sulphides, as 

 potassium sulphide or sodium sulphide, 

 or the common lime-sulphur solution. 



In the investigation of the mildew 

 problem practically all the spray mate- 

 rials known have been tried, and a large 

 number of other substances that sug- 



EXTERNAL STRUCTURE OF AN APHIS 



Colorado Experiment Station 



gested themselves as having some pos- 

 sible value have been prepared and fairly 

 tested. 



Just at this point it is great pleasure 

 to mention the very kindly interest that 

 Mr. Rodgers has continually taken in 

 this work and the valuable assistance he 

 has rendered by giving us unreserved 

 access to his entire orchard, for when 

 experimental spraying is to be carried 

 on there is always a danger of causing 

 serious injury to the trees as well as 

 spoiling the crop, and in the present 

 instance we have accidentally over- 

 stepped that danger line more than once. 



Regarding the value of copper sprays, 

 bordeaux is almost useless for apple mil- 

 dew control in this section, and only 

 one or two of the other copper com- 

 pounds tried have ofTered any hope at all. 



As has been mentioned before, sulphur 

 is the commonest remedy for the mildew 

 group of plant diseases, and at present it 

 is the best remedy we have to ofler for 

 the apple powdery mildew. In fact so 

 far as the mildew is concerned it can 

 be entirely satisfactorily controlled by 

 certain sulphur sprays, but other diffi- 

 culties enter which tend to counteract 

 the good qualities of these sprays. To 

 digress a bit, the longer one is engaged 

 in experimental spraying in this section 

 the more he becomes convinced of the 

 sensitiveness of the trees and the ease 

 with which injury may be brought about. 

 This sensitiveness is undoubtedly the 

 result of the climatic conditions. In 

 fighting fungous diseases by spraying the 

 spray material must have sufificient poi- 

 sonous properties to render it capable of 



Page 57 



FLAT-HEADEd" APPLE TREE BORER 

 (/, Flat-headed larvae; h, Mature beetle; c. Head of 

 mature beetle; d, Pupa. All twice natural size. 



killing the fungus, but must not be sufifi- 

 ciently toxic to injure the crop plant. 

 The fungicide must, therefore, be so 

 selected as to fit into the interval 

 between the killing point for the fungus 

 and the point where injury begins to 

 appear on the host plant. For this val- 

 ley that interval, or leaway, is very nar- 

 row, hence the difficulties that have 

 arisen in the present problem. For 

 instance, certain strengths of commercial 

 lime-sulphur solution and of other sol- 

 uble sulphide solutions that are now 

 quite commonly used in other parts of 

 the United States, with little or no dan- 

 ger of injury to the apple foliage, are 

 entirely out of the question here. Fog 

 no doubt plays a large part in explain- 

 ing the injury to apple foliage that may 

 result in this valley from the use of 

 spray materials that appear to be harm- 

 less in other parts of the United States. 

 The explanation is evidently as follows: 

 Water, and especially atmospheric mois- 

 ture, is capable of dissolving small quan- 

 tities of most any substance that maj' be 

 applied as a spraj^: indeed this solvent 

 action is necessary to accomplish the 



Figure 1, Winged viviparous female of aphis 

 bakeri; 2, Stem mother of aphis bakeri; 3, Wing- 

 less viviparous female of Schizoneura lanigera, 

 showing wax glands; 4, Root galls of woolly aphis 

 of the apple; 5, Eggs of the green apple aphis 

 (aphis pomi) : a. Eggs much enlarged; h. Eggshell 

 after the louse has hatched; c, Apple twig with 

 eggs upon it. Figures 1, 2 and 3 are enlarged 30 

 diameters; Figures 5 a and h enlarged 20 diame- 

 ters; c, enlarged 2 diameters. Colorado Experiment 

 Station. 



