 Since Zyway can move systemically upward in the plant, that's why you'll see some mid-season disease control and even suppression on tar spot. However, you can't expect Zyway to last forever. With most foliar fungicides, we'd say two to three weeks is the maximum residual. With Zyway in furrow, I would expect it to last up to a couple of months. Beyond that, it's time to spray a foliar fungicide if you're concerned about diseases like tar spot, gray leaf spot, or southern rust. I'm Darren Hefty.