I have brown ugly mushrooms growing in my
yard can you tell me what causes this? I routinely fertilize and spray my yard for weeds.

There are all sorts of fungi that will develop in areas where decaying organic matter is present.

One interesting fungus is the puffball mushroom. These pure white to dirty white globes are commonly found in woodland areas and they can reach basketball size. They will explode when mature, releasing a cloud of spores that will fall to the ground and start the lifecycle all over again. So usually once you see them in an area, you should be able to return every fall to view them again.

Of course the most common fungi are the mushroom that will feed off of decaying material like tree roots and mulch. If you have recently removed a tree or large shrub, the roots decaying underground will be a prime feeding source for mushrooms. You can mow over them, or knock or rake them over, but they will likely return. They should run their course within a few weeks, and won’t do any harm to your lawn.