Perhaps the most effective and fastest way to deal with fungal disease, including pythium, is a fungicide called Heritage G. It's granular, so no messy liquids, and lasts 3-4 weeks between applications. You can find it online, Lesco also carries it. It isn't cheap, about one hundred bucks for 30 lbs, but it's rate is 4 lbs./1000 square feet, so if you have a small yard it will last you 2-3 months. Home Depot carries two turf antifungals, but they are marginal at best. If you don't want to go the chemical route then just cut out the area of disease to prevent spread, unfortunately the fungus is in the soil, so it can affect your seedlings at any time.

Wow! I'm glad this came back around. I think everyone has learned something since this thread was started. And now Houzz does notify you when messages you have posted on get more action. So maybe we can tune both of you up at the same time. You should not have to core aerate, ever, with very few exceptions. If you have hard soil there are chemistry reasons and biological reasons for that. The chemistry reason is most often an imbalance in the salts (magnesium, calcium, sodium, and potassium). Those can be addressed with a good soil test. The better lawn forums have been recommending Logan Labs in Ohio for soil testing for the past few years. Their $25 test is what you need. They will email the results to you. If you post them here morpheuspa will give you an extensive reading of the results and get you on your way toward soil perfection. The other reason the soil might be hard and clay-like is biological. There are fungi in the soil that will soften the soil for you once they have been well fed and watered. Spraying the yard with a surfactant will go a long way to allowing water to penetrate the soil and create the environment needed for healthy beneficial fungi. The surfactant can be anything but some are better than others. Ordinary shampoo is a good one. Any clear shampoo, like baby shampoo, will work. Spray the yard at a rate of 3 ounces of shampoo per 1,000 square feet and follow that up with 1/2 inch to 1 inch of water. Allow it 3 weeks to work. If you have other reasons for core aeration, please, lets discuss them. You should also not have to treat for insects unless you have found them in sufficient numbers to treat. The first clue you might have a grub problem is when you see beetles swarming your porch lights in May and June. If you see that then in July, before you see any damage, dig up a square foot of turf down to about 2 inches looking for grubs. If you see fewer than a dozen, then you don't have a grub problem. If you see an uncountable mass of them, then spray. Chinch bugs are more of a southern problem because they like hot soil, but it is possible to see them elsewhere. Spraying insecticide as a preventive measure is not good for the soil biology. Insects are an integral element of healthy soil. Spraying insecticide kills off the bad bugs, but if you don't have bad bugs, then it just kills the beneficial insects. I suspect both of you have watering and mowing height issues. Here's something I wrote a while ago that summarizes what I've learned over the past decade or so. Basics of Lawn Care After reading numerous books and magazines on lawn care, caring for lawns at seven houses in my life, and reading numerous forums where real people write in to discuss their successes and failures, I have decided to side with the real people and dispense with the book and magazine authors. I don't know what star their planet rotates around but it's not mine. With that in mind, here is the collected wisdom of the Internet savvy homeowners and lawn care professionals summarized in a few words. If you follow the advice here you will have conquered at least 50% of all lawn problems. Once you have these three elements mastered, then you can worry about weeds (if you have any), dog spots, and striping your lawn. But if you are not doing these three things, they will be the first three things suggested for you to correct. 1. Watering Water deeply and infrequently. Deeply means at least an inch in every zone, all at once. Infrequently means monthly during the cool months and no more than weekly during the hottest part of summer. Do not spread this out and water for 10 minutes every day. If your grass looks dry before the month/week is up, water longer next time. If that does not work, then you might have to water more than once per week during the summer's hottest period. Deep watering grows deep, drought resistant roots. Infrequent watering allows the top layer of soil to dry completely which kills off many shallow rooted weeds. You will have to learn to judge when to water your own lawn. If you live in El Paso your watering will be different than if you live in Vermont. Adjust your watering to your type of grass, temperature, humidity, wind, and soil type. It is worth noting that this technique is used successfully by professionals in Phoenix, so...just sayin.' The other factors make a difference. If you normally water 1 inch per week and you get 1/2 inch of rain, then adjust and water only 1/2 inch that week. 2. Mowing Every week mulch mow at the highest setting on your mower. Most grasses are the most dense when mowed tall. However, bermuda, centipede, and bent grasses will become the most dense when they are mowed at the lowest setting on your mower. In fact there are special mowers that can mow these grasses down to 1/16 inch. Dense grass shades out weeds, keeps the soil cooler, and uses less water than thin grass. Tall grass can feed the deep roots you developed in #1 above. Tall grass does not grow faster than short grass nor does it look shaggy sooner. Once all your grass is at the same height, tall grass just looks plush. 3. Fertilizing Fertilize regularly. I fertilize 5 times per year using organic fertilizer. Which fertilizer you use is much less important than numbers 1 and 2 above. Follow the directions on the bag and do not overdo it (unless you use organics in which case you may overdo it without fear of hurting anything). At this point you do not have to worry about weed and feed products - remember at this point you are just trying to grow grass, not perfect it. Besides once you are doing these three things correctly, your weed problems should go away without herbicide.

cut & paste from another thread this morning: "Quinclorac kill crabgrass. It's the active ingredient in Drive XLR8, you can use any brand and it will work. Some people (reeljake) uses Sulfosulfuron (Sedge Ender) and it works fine as well. People have have pretty good results keep most weeds out of their bermuda with Celsius and Sulfosulfuron. Plus there is no issues related to applying in hotter temps. Reeljake also uses Dimension with active ingredient dithiopyr as his pre-emergent, I use Prodiamine. With either you want year round coverage to keep ALL WEEDS from germinating. You will need to start your PreM asap to keep winter weeds at bay, then again in Spring for Spring/Summer weeds. PreM: Prodiamine or Dimension Crabgrass: Quinclorac or Sulfosulfuron General weeds (post-emergent): Celsius - 2,4-D will work also but turns grass yellow If you get the correct products, it won't matter what the weed is, it either will never germinate in your yard, thanks to the PreM, or will die when sprayed with the post-emergent."

Looks like there's a fungal issue.