Thanks for the advice yardtractor1!

Do you recommend using a synthetic fertilizer to encourage fast top growth?Like a synthetic 24-0-11?

Regardless, it looks like I will be forced to wait until Tuesday - heavy rains in the forecast, I don't want the fertilizer to wash away before the lawn absorbs it!

You want a fast release (uncoated) synthetic. Urea 46-0-0 is fine. If unsure or you can't find a high first number fast release, use a starter fertilizer with a high first number ( like this). Almost all starters are fast release synthetic. Unless you're facing torrential rains and your lawn is on a hillside, application prior to rain is not a problem and desirable.

Had pretty bad problem last summer and got some good advice in this thread.

http://forums2.gardenweb.com/discussions/3247412/rust-disease-questions

Yes the good news is that it was only rust. You can spray it off the grass and down into the soil using shampoo in a hose end sprayer. Apply about 3 ounces of any clear shampoo (like generic baby shampoo) per 1,000 square feet. Give the soil a chance to dry from your rain first. The shampoo has other benefits, too, but washing fungus off of plants is a big one. Don't substitute dish soap. It is antibacterial and you don't want that.

I think you were watering too long. If you could have gotten 1/3-inch 3x per week that would have been better. Then going forward the idea is to back off on the frequency and maintain 1 inch until the temps cool off (now???). Here's more on watering for mature turf.

Watering: Deep and infrequent is the mantra for watering. This is for all turf grass all over the place. Deep means 1 inch all at one time. Put some cat food or tuna cans around the yard, and time how long it takes your sprinkler(s) to fill all the cans. Memorize that time. That will be the time you water from now on. My hose, sprinkler and water pressure takes 8 full hours to fill the cans. Your time will likely be less. I like gentle watering. As for watering frequency, that depends on the daytime air temperature. With temps in the 90s, deep water once per week. With temps in the 80s, deep water once every 2 weeks. With temps in the 70s, deep water once every 3 weeks. With temps below 70, deep water once a month. Note that you have to keep up with quickly changing temps in the spring and fall. This deep and infrequent schedule works in Phoenix and in Vermont, so it should work for you. The reason for deep and infrequent is to grow deeper, more drought resistant roots and to allow the soil to dry completely at the surface for several days before watering again. If it rains, reset your calendar to account for the rainfall.

That last sentence may need to be modified. The Texas Hill Country received 11 inches of rain on Memorial Day weekend. Subsequently my lawn went 11 weeks with no irrigation at all. Coincidence? 11 inches and 11 weeks? I think some of it was coincidence. If we had a drier climate like West Texas or further west to Palm Springs in CA it would not have lasted 11 weeks.

Thanks for the advice guys!

In hindsight, I was definitely concern when posting earlier! In my defense, the lawn really did transform from looking good to looking BAD very quickly!!

Please see below for an update.

Update: the lawn looks much better already (without me doing anything). The sun actually come thru this weekend/week and I mowed again @ 4 inches today (mowing 2x per week now...). The mower was not coated in rust and the yellowing areas have decreased in size substantially.

I think strange weather (it was overcast for about 1.5weeks and we did get 'torrential rains' (3+ inches one day, 2.xx inches the next etc.) contributed to this problem.

Regardless, I did not take any chances and hit the lawn with fast release synthetic nitrogen after mowing today.

Julian 6A - Thanks for the link! My mower looked like yours - covered in rust in less than 7days time.

Also, I did find another RUST thread that I though was helpful in addition to what everyone added here, in case someone else get hit with a 'rust outbreak'.

http://forums2.gardenweb.com/discussions/1503832/what-kind-of-disease-is-this-rust