But I want to treat with a fungicide and wanted recommendations?

Ordinary Cornmeal @ 20lbs per 1000sqft. It will take a few weeks to work.

I just applied milk at 3 oz - but wanted to know about repeating frequency or if I should try baking soda or something else.

You could use milk every 5-7 days until conditions improve.

Do not spray Baking Soda on the lawn, it could kill it.

Also, water only when 30-50% of the lawn shows signs of stress/wilting. Avoid watering at night. Keep mowing frequently and mow high. Rust usually doesn't reach damaging levels before the grass enters winter dormancy.

According to numerous messages to these forums, corn meal does not work on rust or red thread. Milk apparently does. Another organic solution is garlic juice strained from 2 pounds of garlic pureed with two quarts of water.

Baking soda is the universal fungicide. It should kill red or rusty anything quickly. Unfortunately, being universal, it is non selective and will kill your soil's beneficial fungi, too. There are some grassy plants that seem to rely on the health of surface fungi. Bermuda and St Augustine do not seem to be among those plants but crabgrass does seem to be in that number. Thus, there are some recipes on the market that use baking soda to kill crabgrass in southern lawns. But since baking soda is so hard on the soil microbes, if you used it and left it alone your turf could suffer due to the lack of microbial support. If you were to use baking soda, I would suggest letting it work for 2 weeks and then follow up with compost at the rate of 1 cubic yard per 1,000 square feet or with good compost tea at a rate of a gallon per 1,000 square feet.

Apply baking soda at a rate of 3 ounces per gallon. For a hose end sprayer you could dissolve it in water and concentrate it so the sprayer would dilute it in the mixer. I suddenly need to drive to the big city and can't afford the time it would take to calculate the concentration and dilution, but it isn't that hard (when you're not distracted). Good luck. Looking at the date on your original message you are probably seeing some improvement from the milk.