﻿22 
  THE 
  RED 
  SPIDER 
  ON 
  HOPS 
  IN 
  CALIFORNIA. 
  

  

  Reason 
  for 
  inefficiency. 
  — 
  Some 
  experiments 
  with 
  sulphur 
  upon 
  

   Tetranychus 
  bimaculatus 
  attacking 
  prune, 
  pumpkin, 
  and 
  sweet 
  peas 
  

   proved 
  very 
  satisfactory. 
  Similar 
  results 
  were 
  obtained 
  when 
  

   sulphur 
  was 
  applied 
  to 
  infested 
  sweet 
  peas 
  in 
  Los 
  Angeles, 
  Cal., 
  by 
  

   Mr. 
  H. 
  M. 
  Russell, 
  as 
  is 
  shown 
  in 
  Plate 
  IV, 
  figures 
  1 
  and 
  2. 
  The 
  

   efficiency 
  of 
  sulphur 
  against 
  the 
  red 
  spider 
  on 
  these 
  plants 
  and 
  its 
  

   inefficiency 
  when 
  applied 
  on 
  hops 
  and 
  cotton 
  led 
  to 
  some 
  careful 
  

   observations 
  as 
  to 
  conditions. 
  It 
  was 
  noted 
  that 
  the 
  pumpkin 
  and 
  

   sweet 
  peas 
  expose 
  nearly 
  all 
  of 
  both 
  surfaces 
  of 
  their 
  leaves 
  to 
  the 
  

   direct 
  rays 
  of 
  the 
  sun 
  at 
  some 
  time 
  during 
  the 
  day 
  and 
  that 
  the 
  mites 
  

   on 
  the 
  prune 
  were 
  attacking 
  the 
  upper 
  and 
  therefore 
  the 
  exposed 
  

   surfaces. 
  The 
  hopvines 
  and 
  cotton 
  plants, 
  however, 
  expose 
  princi- 
  

   pally 
  the 
  upper 
  surfaces 
  of 
  the 
  leaves 
  to 
  the 
  sun 
  and 
  the 
  mites 
  living 
  

   upon 
  the 
  undersides 
  are 
  thus 
  protected. 
  

  

  From 
  these 
  observations 
  it 
  is 
  evident 
  that 
  sulphur 
  is 
  effective 
  upon 
  

   the 
  red 
  spiders 
  only 
  when 
  the 
  infested 
  surfaces 
  of 
  the 
  plant 
  are 
  

   exposed 
  to 
  direct 
  sunshine 
  at 
  some 
  time 
  during 
  the 
  day 
  or 
  to 
  intense 
  

   reflected 
  heat. 
  

  

  LIME-SULPHUR 
  SOLUTIONS. 
  

  

  The 
  results 
  obtained 
  in 
  a 
  small 
  preliminary 
  field 
  experiment 
  in 
  

   which 
  lime-sulphur 
  in 
  combination 
  with 
  nicotine 
  sulphate, 
  40 
  per 
  

   cent, 
  was 
  applied 
  gave 
  such 
  good 
  results 
  that 
  these 
  materials 
  were 
  

   at 
  once 
  placed 
  at 
  the 
  head 
  of 
  the 
  list 
  of 
  sprays 
  £o 
  be 
  fully 
  tested 
  out 
  

   during 
  the 
  course 
  of 
  the 
  investigation. 
  The 
  lime-sulphur 
  solutions 
  

   are 
  much 
  cheaper 
  than 
  the 
  nicotine 
  solutions 
  when 
  used 
  at 
  the 
  sum- 
  

   mer 
  dosage; 
  therefore 
  it 
  seemed 
  desirable 
  to 
  try 
  the 
  lime-sulphur 
  

   solution 
  alone 
  in 
  order 
  to 
  reduce 
  the 
  cost 
  of 
  spraying, 
  provided 
  the 
  

   omission 
  of 
  the 
  more 
  expensive 
  nicotine 
  solution 
  did 
  not 
  alter 
  the 
  

   results. 
  

  

  During 
  the 
  early 
  work 
  with 
  these 
  sprays 
  it 
  was 
  evident 
  that 
  the 
  

   straight 
  lime-sulphur 
  solutions, 
  instead 
  of 
  spreading 
  out 
  in 
  a 
  film, 
  

   formed 
  beadlike 
  drops 
  on 
  the 
  foliage. 
  Mites 
  found 
  in 
  actual 
  contact 
  

   with 
  these 
  drops 
  of 
  spray 
  were 
  seen 
  to 
  draw 
  away 
  from 
  them 
  and 
  

   escape 
  uninjured. 
  The 
  results 
  obtained 
  with 
  straight 
  lime-sulphur 
  

   solutions 
  were 
  most 
  unsatisfactory. 
  

  

  Soap 
  formed 
  a 
  precipitate 
  with 
  the 
  polysulphid, 
  and 
  as 
  it 
  was 
  

   very 
  evident 
  that 
  some 
  " 
  spreader" 
  must 
  be 
  used 
  if 
  the 
  lime- 
  

   sulphur 
  solutions 
  were 
  to 
  prove 
  effective, 
  this 
  subject 
  was 
  thoroughly 
  

   investigated. 
  

  

  Upon 
  the 
  suggestion 
  of 
  Prof. 
  A. 
  L. 
  Quaintance, 
  of 
  this 
  bureau, 
  

   " 
  black-strap" 
  molasses, 
  a 
  cheap 
  grade, 
  was 
  used 
  with 
  the 
  lime-sul- 
  

   phur 
  spray 
  at 
  the 
  rate 
  of 
  2 
  gallons 
  to 
  100 
  gallons 
  of 
  spray. 
  This 
  

  

  