Re: Scales

In a message dated 99-07-01 12:04:02 EDT,  Kemberly wrote:

>> Janis -  Is this why when I see the dead scale on the orchids I think my 
problem is  over and sure enough months later the plant is covered again?<<

Yes, precisely.  You see the dead females, but there are eggs hidden under 
her dome just waiting to hatch.  

>>  How do you treat the dormant eggs?<<

Scales are most effectively treated in the crawler stage.  The adult female 
(and thus the eggs under her) are protected by the waxy dome that acts as a 
barrier to insecticides.  But, you can just scrape the adults off  with a 
fingernail, or brush them off with a soft toothbrush.  Rubbing alcohol will 
penetrate the adult shells, you can apply it with a cotton swab to each 
scale.  Of course, these methods are rather impractical with a large plant or 
a bad infestation.  
 
>> What method would you use to completely rid yourself of this problem.....I 
know what kind  of pesticides work and usually I treat for 6 weeks (4 
times)....is this 
 enough?<<

Timing and frequency of treatment depends upon which scale species you have 
because the life cycles differ.  If you can tell me the plants affected, I 
might be able to help.  If you are asking about your orchids, send me a 
private e-mail since houseplants are off topic.  Timing also depends on the 
insecticide you are using.  This information should be on the label.  

The best defense, as always, is healthy plants. Scale infestations can be 
triggered by environmental stress, in particular too much or too little water 
or excessive nitrogen fertilizer.  

Scales have natural enemies -- certain birds, lady beetles and parasitic 
wasps.  Avoid broad-spectrum and persistant insecticides as they will make 
the problem worse by killing the natural predators.  So, if you do use 
insecticides, do so only when they are most effective, when scales are in the 
crawler stage .  Otherwise you will only be spending your time and money to 
make a pest-free environment in which the scales will flourish.  

It helps to know the species of scale, but crawler stage can be monitored by 
putting two-sided sticky tape around the stem of the plant.  Crawlers will 
appear as orange or yellow specks (the size of a period).  Use a hand lens to 
identify them, they are round or oblong with microscopic appendages.  

Insecticidal Soap is environmentally safe and kills the crawlers.  You can 
add alcohol to the mix to treat the adults.  Recipe:  Mix 1 cup isopropyl 
alcohol and  1 tablespoon insecticidal soap concentrate in 1 quart of water.  
Apply every 3 days for 2 weeks.  

You can also use a 2 or 3 percent solution of a narrow-range, light 
horticultural oil (also called supreme or superior oil).  Spray it directly 
on the scales because it works by suffocating them.  This can be safely used 
during the growing season and is less toxic to plants than dormant oils. 

Pyrethrum applied directly to the scales works.  You can combine it with 
isopropyl alcohol (1 tablespoon alcohol to 1 pint diluted pyrethrum mix).  
Make a second treatment 3 to 5 days after the first.  

Finally, as usual, good garden hygene is important.  Don't leave infected 
foliage in the garden, especially over winter.  

--Janis

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