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spider plant & pests

Julie Steele steele at agvax2.ag.ohio-state.edu
Wed Mar 26 13:08:34 EST 1997

Your plants are infested with a very common greenhouse pest, 
Hemispherical Scale, Sassetia coffeae.  These scale insects are 
parthenogenetic (do not need males to reproduce).  Each mature female 
lays 600-700 eggs beneath their bodies and then die.  The eggs hatch into 
crawlers that disperse over the host plant.  Once they settle down and 
begin to feed, they lose their legs and never move again.  They then 
develop a thick waxy shell that is impervious to insecticides.  They also 
produce copious amounts of honeydew- sticky sap like material that 
filters down and coats everything below the plant. Then you will often 
get black sooty mold growth in the honeydew.  While these pests are not 
impossible to erradicate, it will take some time and repeated efforts 
since the adults are minimally affected by insecticides.  My choice of 
insecticide would be Orthene, since it is systemic (taken into the plant 
tissue).  Spray the plant once every two weeks, for at least 2 months.  
The other option is to use isopropyl alcohol (rubbing alcohol).  Dip a 
cotton swab in alcohol and then lightly touch each scale.  You will get 
even better results if you can loosen or lift the shell of the scale 
first.  If this is too labor intensive, you can try spraying the alcohol 
on the plant, but first try it on a few leaves to make sure the alcohol 
will not damage the plant tissue.  New leaves will be the most sensitive. 
 Alcohol can be used on many houseplants safely, such as Boston or 
Maidenhair ferns, parlor palms and Oxalis/ Shamrock plants.  But it will 
damage the young leaves of lemon balm, wax begonia and African violet.  
Good Luck!
(Information taken from "The Scale Insects of Pennsylvania Greenhouses" 
and Rodale's "Organic Gardening", Feb 1986 issue.)

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