Brown spots on lawn could be fungus

Help! Our lawn is looking terrible! We live out on the Redlands, and we were out of irrigation water a week or two ago. We worried about that, but the lawn came through in pretty good shape. We started watering again once it was back on and now a few days later we’re getting great big brown patches in it. What’s going on and are we going to lose the lawn?

— Jay

You’re not alone in dealing with this problem—lots of folks from the Redlands have been coming into the Garden Center this past week with this situation. I can’t be certain without seeing it, but I’m pretty darn sure that you’re dealing with a fungal lawn disease.

There are three fungal diseases common to western Colorado lawns: melting out, ascochyta leaf blight and dollar spot. The truth is that differentiating between them is not that important since their behavior and their control is pretty much the same for all three.

A fourth disease that occurs rarely called necrotic ring spot is a different animal altogether and requires a completely different and much more involved treatment regime.

The important thing to realize is that these three diseases are not aggressive pathogens   —they attack lawns (or portions of lawns) that are weak and under stress for some reason.

Because of this, we encourage people to look deeper for the possible source of stress that predisposed the lawn to develop the disease in the first place. A lush, vigorous, robust lawn rarely, if ever, has problems with these diseases.

Far and away the most common source of stress is watering issues, and I’m sure that’s what’s going on in your case. Too much but especially too little water (either not watering often enough or more commonly, not watering deeply enough) will trigger disease.

The stress on your lawn doesn’t have to be a chronic, week in and week out situation — it can be a one-time problem like what you experienced with the water outage on the Redlands.

Parts of the lawn became drought-stressed, and even though you got the water back on and the grass seemed to recover, that stress was present and that’s all the opening these fungi need to get started.

What I’m telling most people to do right now is just to keep on taking good care of the lawn. Take the opportunity to double check soil moisture, making sure that the soil is watered deeply (at least 8 inches down) but not kept soggy all the time. Giving the lawn the care it needs tips the balance of power back in favor of the lawn and not the disease. If the lawn is happy and healthy, it can fend off the disease on its own.

Now, if you want, you can apply a fungicide to help out. Fungicides are an effective tool to help combat these diseases,  but without correcting any chronic stresses, the disease will reoccur again and again.

The fungicide I usually recommend is Fertilome Systemic Fungicide. It will kill existing infections as well as prevent new ones. Apply it twice, 10 days apart. If the disease isn’t generally spread throughout the lawn, just treat the spot(s) along with several feet of good grass around the margin. Hope this helps.

Dennis Hill is the nursery manager at Bookcliff Gardens, bookliffgardens.com. Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506; or email .(JavaScript must be enabled to view this email address).


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