Each spring when I start tilling and mowing I hang a jug of "Amdro" on the tiller and mower handles then dose each mound I come across.
I dont like to use it in or around the garden but have come to the conclusion its about the only way to keep them under control. If I dont get them killed off early they will start killing the plants when it gets hot and dry.
They will bore through Okra plants at the roots and travel all the way up the stalk and exit at the crown then feed on the blooms and young pods, they make their nests in the roots of other plants and do enough damage that the plants die - they move on to the next one then.
A non toxic way to control them is to pour boiling water into the nest, it will kill them and anything else around the nest so its not a real good solution in all cases but it is a weapon in the arsenal against them.
I have used DE and it does work but it takes forever to complely kill the mound.
