﻿20 
  THE 
  RED 
  SPIDER 
  ON 
  HOPS 
  IN 
  CALIFORNIA. 
  

  

  EXPERIMENTS 
  FOR 
  THE 
  CONTROL 
  OF 
  THE 
  RED 
  SPIDER. 
  

   METHODS 
  OF 
  EXPERIMENTATION. 
  

  

  The 
  sudden 
  and 
  widely 
  distributed 
  appearance 
  of 
  the 
  red 
  spiders 
  in 
  

   the 
  hopyards, 
  the 
  rapidity 
  of 
  their 
  increase, 
  and 
  the 
  fact 
  that 
  the 
  old 
  

   remedy 
  (sulphur) 
  had 
  not 
  controlled 
  the 
  mites 
  in 
  the 
  hopyards 
  during 
  

   the 
  preceding 
  season 
  made 
  the 
  control 
  problem 
  appear 
  a 
  difficult 
  one. 
  

   As 
  soon 
  as 
  the 
  mites 
  became 
  numerous 
  enough 
  on 
  the 
  hopvines 
  to 
  

   warrant 
  experimental 
  work, 
  the 
  first 
  of 
  a 
  long 
  list 
  of 
  experiments 
  

   which 
  was 
  planned 
  during 
  the 
  spring 
  of 
  1911 
  was 
  applied. 
  The 
  lime- 
  

   sulphur 
  solutions, 
  because 
  of 
  their 
  efficiency 
  and 
  relatively 
  low 
  cost, 
  

   soon 
  became 
  the 
  most 
  promising 
  of 
  the 
  contact 
  insecticides. 
  They 
  

   were 
  therefore 
  applied 
  more 
  extensively 
  and 
  were 
  given 
  more 
  atten- 
  

   tion 
  than 
  the 
  other 
  materials 
  which 
  were 
  listed 
  during 
  the 
  investiga- 
  

   tion. 
  

  

  The 
  materials 
  were 
  applied, 
  except 
  in 
  the 
  small-scale 
  work, 
  with 
  a 
  

   power 
  outfit 
  (PL 
  III, 
  fig. 
  1) 
  which 
  maintained 
  from 
  120 
  to 
  150 
  pounds 
  

   pressure. 
  Seven-foot 
  rods 
  tipped 
  with 
  a 
  nozzle 
  throwing 
  a 
  fine 
  but 
  

   washing 
  spray 
  were 
  used 
  for 
  the 
  work. 
  

  

  In 
  making 
  the 
  tests 
  with 
  the 
  various 
  insecticides 
  it 
  was 
  found 
  

   desirable 
  to 
  express 
  their 
  efficiency 
  with 
  as 
  near 
  an 
  approach 
  to 
  

   numerical 
  exactness 
  as 
  possible. 
  Tag 
  counts 
  and 
  field 
  counts 
  were 
  

   employed 
  in 
  obtaining 
  the 
  percentage 
  of 
  mites 
  killed 
  and 
  were 
  found 
  

   to 
  be 
  very 
  accurate. 
  In 
  most 
  cases 
  only 
  one 
  of 
  these 
  methods 
  was 
  

   used 
  on 
  a 
  plat, 
  but 
  occasionally 
  both 
  were 
  employed. 
  These 
  counts 
  

   were 
  made 
  both 
  before 
  and 
  after 
  spraying. 
  

  

  Tag 
  counts. 
  — 
  Twenty 
  tags 
  were 
  attached 
  to 
  the 
  petioles 
  of 
  as 
  many 
  

   leaves, 
  and 
  the 
  numbers 
  of 
  mites 
  found 
  upon 
  the 
  several 
  leaves, 
  both 
  

   before 
  and 
  after 
  spraying, 
  were 
  recorded 
  upon 
  the 
  attached 
  tags. 
  

   The 
  percentage 
  of 
  mites 
  killed 
  by 
  the 
  spray 
  was 
  thus 
  very 
  accurately 
  

   obtained. 
  

  

  Field 
  counts. 
  — 
  Field 
  counts 
  were 
  made 
  by 
  picking 
  20 
  leaves 
  from 
  

   various 
  parts 
  of 
  as 
  many 
  vines 
  chosen 
  throughout 
  the 
  plat. 
  The 
  

   numbers 
  of 
  mites 
  found 
  upon 
  the 
  leaves, 
  which 
  were 
  taken 
  bbth 
  before 
  

   and 
  after 
  spraying, 
  were 
  compared 
  and 
  the 
  precentage 
  of 
  mortality 
  

   obtained. 
  This 
  method 
  gave 
  a 
  good 
  idea 
  of 
  field 
  conditions 
  but 
  did 
  

   not 
  prove 
  as 
  effective 
  as 
  the 
  tag 
  count. 
  

  

  SULPHUR. 
  

  

  Sulphur 
  in 
  a 
  dry 
  and 
  finely 
  divided 
  form 
  has 
  in 
  past 
  years 
  been 
  used 
  

   very 
  extensively 
  against 
  red 
  spiders 
  with 
  supposedly 
  good 
  results. 
  

   One 
  experimenter 
  states 
  that 
  although 
  the 
  sulphur 
  does 
  not 
  affect 
  the 
  

   adult 
  mites, 
  it 
  kills 
  the 
  larvae 
  when 
  they 
  emerge 
  from 
  the 
  eggs 
  and 
  

   thus 
  checks 
  the 
  infestation. 
  Several 
  hop 
  growers 
  stated 
  that 
  the 
  red 
  

  

  