Preservative composition for lignocellulosic-based composites providing rapid and long-lasting protection against insect and fungal attack, in both low and high moisture environments, through the use of a combination of higher solubility and lower solubility borates. Pesticidal amounts of a lower solubility borate and a higher solubility borate are combined before or during their incorporation into a lignocellulosic-based composite. Useful low solubility borates include copper borate, zinc borate and barium metaborate. Useful high solubility borates include boric acid, boric oxide, ammonium borate and alkali metal borates such as sodium borate. Some alkaline earth metal borates, including calcium borates, calcium magnesium borates, magnesium borates and calcium sodium borates, are of intermediate solubility and may be used effectively as either a low soluble or high soluble borate depending on the combination used.