Other than watering deeply, I have a couple questions about what I should be doing next:
1) What are the differences between corn meal as a fertilizer and the Garden-ville fertilizer I am using? Which is preferable for controlling fungus, which I have had problems with in the past?
The difference is ingredients and cost. I think I get the same results from applying only corn meal as I would if I applied a commercially bagged organic fertilizer that costs 6x more. Pure ordinary corn meal is the only material that has a long record of 'curing' fungal diseases. Coffee grounds might do the same thing but the lawn experience with coffee is lacking. Apparently mushroom growers do not use coffee because it is anti fungal.
2) When should I fertilize next?
I fertilize on the federal holidays. They are easy to remember and they work for me. I start on Washington's Birthday, then Memorial Day, 4th of July, Labor Day, and Thanksgiving. Washington's Birthday happens to fall 3 weeks prior to the 'last frost' date in San Antonio. Usually there are specific trees in bloom and I could use those as my start date. Look for the day the redbud trees start to show and fertilize then. The application rate for all grain type fertilizers is 10-20 pounds per 1,000 square feet. Then wait 3 full weeks to evaluate whether you used enough and adjust from there. You can apply twice as much with no harm but there's not necessarily any benefit to using more.
3) I tend to see lots of weeds in the early spring and late fall. I missed the opportunity to control them with corn gluten this spring, and next year will put it down by mid-February. Can I also apply it late in the fall to control late season weeds?
If you have St Aug you should be mowing at the highest position on your mower deck. If you combine the deep infrequent watering with mowing high, you should have minimal weed problems. The weeds you see in early spring are wild flowers that sprouted from seed last fall. Check with your local county extension agent to find out when the wild flower seeds germinate. Still there are certain weeds that might get started that will choke out St Augustine. Those include dichondra, henbit, clover, and oxalis. You will have to pull those out by hand or spray them on a hot, sunny day with strong vinegar. Vinegar will also kill St Aug so try to shield the spray from the grass and only get it on the weed.
4) How often should I apply beneficial nematodes?
Usually twice a year is plenty. Once in late winter will take out ticks, thrips, and fleas. Another application when you see June bugs swarming your porch lights will take out fleas and June bug larvae.
Beneficial nematodes work best when it is raining hard. They need lots of moisture to move around. They are extremely prolific if there are plenty of host critters in the soil. Interestingly they kill the host by infecting them with a disease that only affects insects. I have not used beneficial nematodes in years...of course we have not had much rain in the past few years.