How blunt mower blades damage your lawn: Thought it was fungal? It might be your mower blades
This was from a job this morning. I thought I was walking into a fungal issue, but it turned out to be blunt mower blades. A sharp blade slices the grass leaf cleanly. A dull blade doesn’t cut, it tears. The difference shows up the next day. Look closely at the tips of a freshly mown lawn cut with blunt blades and you’ll see frayed ends where the leaf has been ripped rather than sliced. Those torn ends dry back into a brown stub, which gives the lawn that pale, off-colour look 24–48 hours after mowing.That torn surface is also a wide-open entry point for fungal pathogens, especially in damp conditions when disease pressure is high. Clean cuts heal quickly, torn cuts don’t.
There are no signs of fungal lesions anywhere on the leaf, this is purely cutting damage. It is a good idea to sharpen rotary mowers about every 20-25 hours of use.
I wonder if they've been putting brews down before/after mowing? At this time of the year I don't like mowing soon after a foliar brew. I find the new growth that's been pumped up by the brew is softer and more prone to tearing.
The common advice is to wait 4-6 hours after a foliar before mowing, but I personally leave it 2-3 days when its colder. The leaf hasn't had time to firm up the new tissue with lignin and structural components, so the mower shreds it instead of slicing it cleanly. That's where you get those torn, frayed leaf tips that dry back over the next couple of days.
The way I run it now it's cooled down is mow first, wait around 6 hours for the ends to heal, then put the brew down. After that I leave it 2-3 days before the next mow so the new growth has time to harden off, otherwise you're back to the same problem.
@Jonny Hicks and @Garry B thanks for sharing this. I had no idea about this when using liquids.