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I just installed couch lawn a few weeks ago. It was thriving, until I started noticing yellow patches which are spreading. I have attached pictures.
Welcome to the Bunnings Workshop community @Missmusonza. It's wonderful to have you join us, and many thanks for your question about lawn care.
I'm so sorry to hear this. That must be devastating.
With newly laid couch turf that was doing well and then suddenly develops yellow patches that spread with very sharp, defined edges, the pattern itself gives a lot of clues.
The first thing to understand is that the couch generally yellows evenly when it is stressed by watering or nutrition issues. Those problems tend to look more gradual and patchy, with the surrounding grass also looking a bit weak. What you are showing here is a very clear line between healthy green turf and yellow or dead turf. That sharp boundary is not typical of watering issues or normal establishment stress.
Fungal problems can affect new lawns, especially in warm, humid conditions, but they usually create softer edges. The grass around the affected area often looks dull, slimy, or mottled before it fully yellows out. The damage tends to creep rather than appear as a clean division between living and dying turf.
One of the most common causes of this exact look is chemical damage. Even a small amount of herbicide overspray can do this. Products like glyphosate, or even strong selective weedkillers used incorrectly, create that very distinct line where the spray stopped. It does not take much, and it can happen from spray drift, contaminated watering equipment, or a spot treatment done nearby.
Dog urine can cause yellowing, but it usually shows as small circular patches with darker green growth around the edges rather than large spreading sections with straight or defined borders. From what you are showing, that seems less likely.
If the turf was recently purchased, it is worth contacting the turf supplier and showing them the photos. They are very familiar with establishment issues and can often identify whether it looks like chemical damage, disease, or something related to turf handling. Unfortunately, if it is a chemical burn, the affected turf generally will not recover, and replacement of those sections is usually the only fix. The healthy surrounding couch should continue to thrive once the cause is identified and removed.
Please let me know if you have any questions.
Mitchell
