Yes, but...you can. I see it in San Antonio all the time. The ONLY secret is to keep the St Augustine watered once a week (very deeply if possible). The secondary secret to allow full coverage for St Aug is to mow at your mower's highest settinng. In those circumstances, in San Antonio, St Aug wins out every time. But if you stop watering for a couple weeks then suddenly the entire area will be bermuda. I have done this myself and gone back and forth. My driveway in the back is stone. The St Aug escaped into it years ago and the bermuda volunteered. We never water the area except for my experiments with shifting back and forth from one grass to the other. In my absence and a drought year, the St Aug is all gone now. Oh and I always forget about the load of dirt the city used to backfill a repair on my water meter. It grew nutgrass and bermuda, but the St Aug filled back in. I did nothing and now it is all St Aug. Here's the problem in a nutshell. When there is a drought, if you don't water bermuda, it goes dormant and will return at the first sign of moisture. If you don't water St Augustine, it goes dead and will not return, period. So if you have an unirrigated and mixed lawn, the bermuda will win. But at the same time, bermuda cannot tolerate any shade. That's why you have areas of St Aug now. They are in the shade of something (fence, building, tree, etc.). Since bermuda is so sun loving, anything you can do to shade it will give the edge to the St Augustine. Mowing the grass at the highest setting will provide enough shade from the St Augustine to choke out the bermuda. St Augustine will spread 10 feet in all directions in one season. A few strategically placed flats (about $1 each at most SA nurseries) should give you a full St Aug lawn by October. If you are going to get on an organic program, now is a good time to start with fertilizer. If you are on a chemical program, do not fertilize until after you mow real grass (not weeds) for the second time. Waiting like that ensures you are putting fertilizer on active grass roots and not just weed roots. My lawn could not be easier to care for. I changed to organic in 2002 and life got real easy. All I have to do is water deeply once a week, mow high (as high as my wife will let me), and fertilize on the federal holidays. I only get weeds in the back where the dog and kids live. There is a FAQ on organic lawn care over on the Organic Gardening forum. It describes an inexpensive, clean, and very effective program.

really hard to tell for sure but typically fungus in my area is reddish/yellow. You may have multiple problems. The problem with newbies is that they want to solve problems with chemicals (I was one of the worst offenders). The worst time to add fertilizer is when a grass is stressed and excessive nitrogen will show up as patterns matching the application method. If you just applied the nitrogen within the last few days you can reduce the effect by watering heavily for one day but if you applied it more than a few days ago you are probably past the danger period. Again, check the soil moisture at about 2-6" deep at several areas in your lawn each week. It should be slightly wet the day of watering and then let it go to slightly damp before watering again. Wet all the time just rots the roots and causes yellowing due to lack of nutrients. With most soils a twice weekly 1" watering in the summer is all you need. When the grass comes back on it's own (and I'm almost certain it will) then evaluate the soil like I said and take any corrective action required. Guessing and throwing chemicals at it will probably make things worse.

Are you cutting at the same height as the old mower, or trying to go lower? Any other differences between the old mower & new? Maybe the old one had a higher blade count or something? I'd check the Fiskars to make sure everything is aligned properly, but it's only 5 blades, so some tufting, pulling & ridges are expected. I'd also like a close up of the bad spots when you get a chance. Did you buy the bagger for the Fiskars?

There's a good chance your neighbor doesn't know what problem he has/had. Grubs are easy to find. Dig up 1 square foot of turf. If you can count fewer than a dozen grubs, you don't have a problem. If you have an uncountable mass of grubs, then you have a problem. A lot of people don't know what crabgrass looks like and believe that the weed they have is crabgrass. The problem is trying to treat a weed that is not crabgrass often does not work. Crabgrass is a summer annual plant that will get a good start in mid to late spring IF THE SOIL STAYS WET FOR A FEW DAYS IN A ROW. Crabgrass seed needs full sunlight and continued moisture over several days. If you maintain tall turf, say 3+ inches high, that will go a long way to preventing crabgrass from ever getting started. But if the grass thins out from disease or grubs, then crabgrass can break in the following spring. But it also needs continual moisture. This is one reason why seeding northern grasses in the spring is a bad idea, because the same treatment used for germinating new grass seed is ideal for germinating crabgrass seed. And the crabgrass will germinate faster than any of the cool season grass seeds giving you the impression that you're a lawn genius. Many people will pull back on watering just before the real grass seed germinates. What they end up with is a full crabgrass lawn by July. Crabgrass will completely die after the first frost of autumn. With this in mind, I'm going to suggest you do not water twice a week during spring and only do that when the temps are real close to 100 degrees F. Once a week with temps in the 90s should be fine as long as you water 1 full inch, all at one time. You can treat your hard soil by spraying it with baby shampoo at a rate of 3 ounces per 1,000 square feet. Or you could do 3 ounces per 100 square feet. It's not going to hurt anything if you use too much. Follow that up with 1/2 to 1 inch of irrigation or rain to take the shampoo deep into the soil. If water runs off rather than soaking in, stop watering immediately and wait 15 to 30 minutes for the water to soak in. Then resume until you get the 1/2 to 1 inch. You can measure the water with a tuna can or cat food can. The shampoo works by setting up the perfect environment underground for holding moisture and keeping it cool. The microbes living in the soil will soften it for you. Give it 3 weeks to see the improvement. If you have bare spots now, rather than seeding in the spring, it would be better if you could cover it with sod. The sod will help keep the crabgrass seed from germinating if it is already there.