The Forestry Forum

What are you guys spraying your air dried lumber with for insects? thanks.

98% disodium octaborate tetrahydrate.  Two brand names are Timbor and Solubor.

Danny,
Do you spray any of it after it's dried or only when still green?

I spray green.  If it is air dry, the PPB's could already have laid eggs and have larvae inside the wood.  Spraying at that point will prevent re-infestation, but you already have them in the wood, so it is too late. 

I would also think you risk staining and warp by spraying dried lumber depending on how wet you spray.

The main insect is the ambrosia beetle that attacks air drying lumber.  The lyctid powderpost beetle attacks well air dried and kiln dried lumber.  Both make 1/16" diameter holes.

Large commercial operations do not spray lumber before or during air drying.  A few sawmills do dip their lumber in a fungicide in warm weather.  Sometimes, the dip has an insecticide too.  Most mills do not dip for insects.  The risk of insect damage increases with time and lower MCs.  Commercial air drying is often just 90 days, so the risk is small.  Also, the best control for insects is to keep the air yard free of wood debris.  The insects do not fly in from the neighbors but breed in wood debris in the yard.  Clean up the wood often.  Run the untreated 4x4s through the kiln once or twice a year.

A kiln heating wood to 133 F will kill all insects and eggs.  Keep this KD wood separated from air drying wood to prevent re-infection after drying.  Keep kiln dry storage areas clean.  Never bring in wood dried by someone else, especially foreign wood, into your KD area.

Note that large operations can lose a pile without much financial damage, but a small operation might find a one pile loss to be very costly.

Note that borates and some other insecticides are water soluble, so rain will wash them away.

As noted, sprays and dips only provide a poisoned, protective layer on the outside of the lumber, so any insects inside are not affected...treat right after sawing.