You can apply too much Prodiamine but the good news is that the impacts won’t likely be disastrous. The biggest issue you might see is that the Prodiamine becomes less effective. This is because, when you over apply this product, it causes microbes in your lawn to break it down too quickly and to multiply at an undesired rate. So in effect, applying too much Prodiamine ends up leaving you with less Prodiamine overall.