﻿THE 
  RED 
  SPIDER 
  ON 
  HOPS 
  IN 
  THE 
  SACRAMENTO 
  

   VALLEY 
  OF 
  CALIFORNIA. 
  

  

  INTRODUCTION. 
  

  

  The 
  common 
  "red 
  spider" 
  (Tetranychus 
  bimaculatus 
  Harvey) 
  has 
  

   long 
  been 
  known 
  as 
  a 
  pest 
  in 
  flower 
  gardens 
  and 
  greenhouses, 
  where 
  

   it 
  is 
  often 
  very 
  injurious 
  on 
  ornamental 
  plants. 
  This 
  damage, 
  how- 
  

   ever, 
  becomes 
  quite 
  insignificant 
  when 
  the 
  injury 
  to 
  hopvines 
  is 
  con- 
  

   sidered. 
  During 
  the 
  past 
  few 
  years 
  this 
  mite 
  has 
  become 
  recognized 
  

   as 
  one 
  of 
  the 
  most 
  injurious 
  of 
  hop 
  pests 
  on 
  the 
  Pacific 
  coast 
  and 
  

   especially 
  so 
  in 
  the 
  Sacramento 
  Valley 
  of 
  California. 
  

  

  The 
  investigation 
  upon 
  which 
  this 
  bulletin 
  is 
  based 
  was 
  begun 
  

   January 
  1, 
  1911, 
  at 
  the 
  request 
  of 
  the 
  horticultural 
  commission 
  of 
  

   Sacramento 
  County 
  and 
  in 
  cooperation 
  with 
  the 
  E. 
  Clemens 
  Horst 
  

   Hop 
  Co., 
  of 
  San 
  Francisco, 
  and 
  extended 
  over 
  a 
  period 
  of 
  18 
  months. 
  

   Observations 
  were 
  made 
  throughout 
  this 
  period 
  in 
  the 
  hop 
  fields 
  in 
  

   all 
  parts 
  of 
  the 
  Sacramento 
  Valley, 
  and 
  spraying 
  experiments 
  were 
  

   conducted 
  on 
  both 
  a 
  large 
  and 
  a 
  small 
  scale. 
  

  

  The 
  recorded 
  efficiency 
  of 
  the 
  various 
  insecticides 
  tested 
  during 
  this 
  

   investigation 
  is 
  based 
  upon 
  actual 
  counts 
  of 
  mites 
  present 
  before 
  and 
  

   after 
  spraying, 
  as 
  well 
  as 
  upon 
  general 
  observations 
  under 
  ordinary 
  

   field 
  conditions. 
  

  

  ECONOMIC 
  IMPORTANCE. 
  

  

  The 
  red 
  spider 
  was 
  reported 
  in 
  injurious 
  numbers 
  in 
  the 
  hop 
  fields 
  

   at 
  Wheatland, 
  Yuba 
  County, 
  Cal., 
  in 
  1902. 
  Since 
  then 
  it 
  has 
  done 
  

   some 
  injury 
  to 
  hops 
  in 
  the 
  Sacramento 
  Valley 
  every 
  year 
  and 
  in 
  1910 
  

   the 
  hop 
  crop 
  was 
  seriously 
  injured 
  in 
  many 
  localities. 
  One 
  company, 
  

   the 
  E. 
  Clemens 
  Horst 
  Co., 
  estimated 
  their 
  financial 
  loss 
  due 
  to 
  this 
  

   mite 
  in 
  a 
  few 
  of 
  their 
  hopyards 
  near 
  Sacramento, 
  Cal. 
  (allowing 
  14 
  

   cents 
  per 
  pound 
  for 
  hops), 
  to 
  be 
  from 
  $10 
  to 
  $68 
  per 
  acre. 
  Other 
  

   growers 
  were 
  not 
  able 
  to 
  pick 
  their 
  hops 
  so 
  rapidly 
  as 
  did 
  this 
  com- 
  

   pany, 
  and 
  their 
  loss 
  was 
  necessarily 
  much 
  greater. 
  In 
  some 
  yards 
  

   near 
  Sacramento 
  the 
  hops 
  were 
  so 
  badly 
  injured 
  that 
  they 
  could 
  not 
  

   be 
  picked 
  at 
  all 
  and 
  were 
  allowed 
  to 
  remain 
  in 
  the 
  field. 
  

  

  Note.— 
  Obligations 
  are 
  due 
  to 
  the 
  manager 
  of 
  the 
  K. 
  Clemens 
  Hoisl 
  Co. 
  and 
  to 
  the 
  superintendent 
  of 
  the 
  

   ranches 
  at 
  Perkins 
  and 
  at 
  Wheatland, 
  who 
  placed 
  at 
  my 
  disposal 
  every 
  means 
  possible 
  to 
  carry 
  on 
  the 
  work; 
  

  

  to 
  I'rof. 
  w. 
  15. 
  Menus, 
  (or 
  many 
  valuable 
  suggestions; 
  to 
  Mr. 
  B. 
  EL 
  Carnes, 
  superintendent 
  of 
  the 
  State 
  

  

  insectary, 
  Sacramento, 
  Cal., 
  who 
  generously 
  provided 
  me 
  with 
  desk 
  room; 
  and 
  to 
  Dr. 
  i". 
  11. 
  Chittenden, 
  

   under 
  whose 
  directions 
  the 
  investigation 
  was 
  carried 
  on.— 
  W. 
  13. 
  1". 
  

  

  9 
  

  

  