The cottony maple scale outbreak described in last weeks newsletter seems to be very limited in distribution. So far, the noticeable presence of the scales fluffy white egg cases on the twigs of silver maple trees has been reported in the relatively small triangular area of NW Iowa between Kossuth, Greene and Sac counties, and in Black Hawk County. Other isolated infestations are certainly possible.

The following points recap the highlights of this pest.

• A cottony maple scale outbreak will not kill the trees.
  
• Only silver maples are likely to be heavily infested though other trees may have some scales.
  
• Treatment is not advised.
  
• Treatment is unnecessary and environmentally disruptive.
  
• ISU advice is to endure the temporary annoyance if possible.
  
• If small trees or trees overhanging decks, etc. MUST be sprayed, wait until early July.
  
• Two treatments are necessary.
  
• Homeowners are encouraged to spray with insecticidal soap if they decide to spray in spite of the absence of any direct threat to tree health and vigor.

Soap or detergent sprays are non-toxic to applicators and people and pets in the yard. They are also less toxic to predators and other natural enemies than are the standard insecticides such as malathion, diazinon, Sevin, Orthene and Isotox.

Insecticidal soap is available from garden center, hardware and department stores under various trade names. Look for a product that lists as the active ingredient "potassium or sodium salts of fatty acids." Mix and apply commercial products according to label directions.

You may substitute ordinary dishwashing detergents for the commercial products with little risk of injury to maple trees. To make your own insecticidal soap spray solution, mix 5 tablespoons of liquid dishwashing detergent in 1 gallon of water.

Soap sprays have no residual activity and only control insects that are contacted directly. Thorough spraying of leaf undersides is important for control.

This article originally appeared in the June 17, 1994 issue, p. 91.