Did you fertilize earlier in the year? You should not have. If you did and you only mow once a week, then this sort of thing happens. Waiting until late May (Memorial Day) for your first spring fertilizer will avoid this kind of rapid growth.

Apparently you do not mow at your mower's highest setting. Reset your mower to the highest setting for your normal mowing season. This works for all grasses except bermuda, centipede, and creeping bentgrass.

If you still get grass clumping then go over it again to remulch and blow the smaller pieces down into the turf. I'm taking a break from doing that very thing, right now. My free time has been taken over by a condo remodel, so I have not mowed in a month. It's long, but I'm going over it twice to get the loose grass spread out.

Really just a function of too much grass cut that cannot be immediately dispersed. I get this all the time. Sometimes I have to go over the clumps again. Doesn't look like you have that many clumps either. Stick to cutting no more than a third of the blade (a golden rule) but sometimes you just have to cut before this or double cut.

I have to cut twice a week to avoid clumping.

I need to cut twice a week . i didn't want my grass to be too short. wanted to keep at around 4 inches . I also need to check my mulcher to make sure it's doing it's bit. I haven't fertiliser it yet so that's next . hopefully it's all lush and beautiful soon .

Unless you are taking a significant amount of grass off, or it has gotten out of control, any rotary mower can handle this situation. Instead of blowing the grass clippings into the are that you have already mowed, mow so that the grass cuttings are blown into the uncut grass. This gives you successive cuts over the grass and effectively mulches it with out a mulching attachment.

I mowed my grass by blowing the grass into the uncut ares, and very rarely do I have to worry about the dead grass rows you are seeing. When I do it is a simple task to run the mower over it, or use a leaf blower to spread it over the yard.

Cutting too much at a time, cutting when the grass is wet, or a combination of the two will cause clumping. Some mulching mowers can handle more grass than others. Also, early spring the grass holds more moisture than later in the summer months which can lead to clumping.

Keeping your mower blades sharp will help a lot too and is much easier on the lawn. I cut mine at 4" and occasionally due to rain or something else going on it may get a little out of control. When this happens raise the deck and cut it a little higher, then go back a couple days later and mow at your normal height. Learn what your mower can handle and mow whenever it needs it.