Breakout of "yellow-patch" in St. Augustine turfgrass

[lep]

A pattern I have observed over the last few years is that as soon as the temperature drops (we are in Texas), something appears to cause the lawn to lose its immunity, such that small regions turn yellow and then die rather quickly. I have been able to maintain a thick dark-green turf all year (since spring) and fundamentally, there is no reason why anything needs to change as soon as we get the first cold snap -- but something does occur. A yellow rust-type fungus sets in very quickly and grass in these regions dies rapidly, and all you see is dead grass. The remaining areas seem just like the rich dark green during spring-summer type.

I pretty much keep the insect infestation down by use of neem oil, and have noticed there are no chomped up blades of grass suggesting anything like sod-webworms or cutworms. I also haven't been hit with any brown spot or fungal infection all summer long. Through the latter part of summer we only used the irrigation system (1/2" water) twice a week and now I will turn it off if it rains.

There must be some type of cycling the plant goes through after the first few periods of temp drop, causing poor immunity. Are there any organic applications (rules of thumb, independent from soil test pH, etc.) which can knock or alter this dormant-immunity switching mechanism?

[Kiril]

Got pictures?

[Landscape Poet]

Originally Posted by lep

A pattern I have observed over the last few years is that as soon as the temperature drops (we are in Texas), something appears to cause the lawn to lose its immunity, such that small regions turn yellow and then die rather quickly. I have been able to maintain a thick dark-green turf all year (since spring) and fundamentally, there is no reason why anything needs to change as soon as we get the first cold snap -- but something does occur. A yellow rust-type fungus sets in very quickly and grass in these regions dies rapidly, and all you see is dead grass. The remaining areas seem just like the rich dark green during spring-summer type.

I pretty much keep the insect infestation down by use of neem oil, and have noticed there are no chomped up blades of grass suggesting anything like sod-webworms or cutworms. I also haven't been hit with any brown spot or fungal infection all summer long. Through the latter part of summer we only used the irrigation system (1/2" water) twice a week and now I will turn it off if it rains.

There must be some type of cycling the plant goes through after the first few periods of temp drop, causing poor immunity. Are there any organic applications (rules of thumb, independent from soil test pH, etc.) which can knock or alter this dormant-immunity switching mechanism?

I am thinking given the outbreaks are during cold period I would start by looking and seeing if it is Brown Patch. Come over to the FL forum at the bottom of the forum page right below pesticide forum link and look for the BP thread. We have several photos up of different outbreaks there so you can see real field photos to help you ID it if it is indeed BP.
It could be a variety of things including different fungus but I would start there looking at brown patch.

[PlantscapeSolutions]

The problem you see is caused by a soil born fungus that flares up in the fall when air and soil temps get just right. Usually, it's when the first fall cool fronts roll in around late September thru mid October. If we get a warm November like we did this year the season for fungal issues will be longer.

The fungal issues that can occur during periods of wet cloudy weather in spring or summer is not the same. The use of Anderson's Golf Products Compass Fungicide will cure either of these problems.

In my opinion it is fall fungal issues that cause all turf grass's growth rate to taper off suddenly in October. But only the St. Augustine is so genetically flawed that it gets the classic fungal rings.