UNDATED (MNN) -  Minnesota Department of Agriculture officials are ramping up with their yearly effort to fight off invasive tree pests.  Aside from lots of purple traps being set in ash trees for emerald ash borer, the fight against gypsy moths begins soon.  Traps going up around central Minnesota include three areas in the west, north and east metro.  The Ag Department's Allen Sommerfeld says the largest area of gypsy moth traps will again be on Minnesota's North Shore and in the Duluth area.  Traps are set to go up by the end of the month.