I correctly applied the pre-emergent crabgrass prevention in the spring, and no crabgrass came up. Fast forward to late July/early August, and crabgrass has grown rapidly in my lawn. I’ve seen this all over the area as well. Is there a second time period we should apply more pre-emergent in the summer to avoid this late season resurgence?
No, no second application should be necessary. If your spring application was properly timed and applied as the Forsythia flowers are falling to the ground (not when they are on the shrub) which is the same time as the lilacs are opening, you should have prevented the crabgrass. The most common mistake is applying too early. This spring was tricky because cool weather held the forsythia flowers on the shrubs longer than usual. Many people were fooled into applying too early…as usual.