Here is a description of wormgaurd:
Organic poultry dewormer is safe and natural; FDA approved. Concentrated food grade diatomaceous earth, whole flaxseed, grape seed extract as well as 4 strain of Lactic acid bacteria for improved digestion and feed conversion. Feed daily to keep poultry worm free. Add 3 cups to 50 lbs of feed or 1 tablespoon to 1 lb of feed. Mix well. No egg or meat discard. Safe for us in layers and broilers.
With those ingredients, I seriously doubt it could eradicate an actual infestation. DE is a preventative, not a de-wormer. If you want to try it, I would be prepared to test again for worms (fecal float), and use a proven de-wormer if necessary.