If you want to maintain your fence in a good condition, you should spray it and keep it in good health. You can use good insecticides from companies such as Ronseal. Incidentally, Ronseal also gives you the sprayers which can do the job effectively. Take for example the Pump Sprayer which Ronseal has introduced. It is a pressurised sprayer. It requires no assembly. It is a ready to use sprayer. It delivers fast, accurate and even coverage. It requires no power or battery. It is much faster than a brush. You can complete treating one panel in about 3 minutes time. You can use any Ronseal product with it.