March 2019 Ready, Set, Grow!

We may still have a day or two of cool weather to deal with but spring is definitely here. A mild winter and mostly warm spring has led to an early green-up of lawn grasses. That early growth also leaves us open to turf diseases, especially brown patch. It’s also been excellent weather for weeds but that’s another story.

Brown patch (also known as “large patch”) is probably the most common disease we see in turf grass. It’s most prevalent in fall and spring with relatively cool (below 80 degrees) temperatures and high humidity. Believe it or not, humidity is lower during the day in hotter months, as the sun evaporates morning moisture more quickly.

A fungal organism called Rhizoctonia solani is the culprit, and it likes fresh growth and lots of water. Many lawns never went completely dormant this winter and Lord knows we had enough rain. We see this disease more often in lawns that were over-fertilized or fertilized at the wrong time as well. While it might have been tempting to fertilize in February, that could have led to more problems. Late March is the earliest we should fertilize.

So how do you know if you have brown patch? Well, if you have St. Augustine or centipede grass (the vast majority in our area) and it’s brown now, there are few other likely causes. (It may attack other grasses, but these are the most common hosts.) Chinch bugs attack in summer and tend to cause similar but very irregular damage. Large patch can be pretty irregular as well, but closer inspection often shows several overlapping circles.

As I said, it’s more common in cool weather. But even in summer, improper watering can make fungal diseases worse. Always water early in the morning. Evening watering will leave the leaf blades wet overnight, giving the fungus plenty time to make itself at home. Also, water deeply (the equivalent of at least one or two inches of rain) once a week. Daily watering is too frequent and again you’re leaving leaves wet too long.

If you do have brown patch, chemical treatment can help. Fungicides are available in granular and liquid formulations. Granulars are fine as preventive treatments, but the liquids will give you better coverage in areas already affected. Granular formulas will need to be watered in, but liquids should be allowed to dry on the leaf blades to be effective.

Systemic fungicides are your best bet, as they stay in the plant’s vascular system for a while. These include the active ingredients (fine print on the fungicide bag) propiconazole, myclobutanil, thiophanate-methyl, and chlorothalonil. Brand names include Scott’s Disease Ex, Fung-onil, Spectricide Immunox Lawn Disease Control, Bayer Advanced Fungus Control for Lawns, and several others. Use them according to label directions and they should be perfectly safe for pets, kids, and other yard-dwellers.

These chemicals aren’t miracle workers, so expect to re-apply fungicide (per label directions) a couple more times. Do realize that just about all our fungicides are better preventive agents than curative. The brown blades of grass will not turn green, but their growing and your mowing will eventually take the brown parts off. The result is ultimately a green lawn. Success can be better measured by the fact that the disease is no longer spreading.

If you want to know more about gardening, landscaping, or anything else horticultural, contact the St. John, St. James, & St. Charles Parishes County Agent André Brock at Also, the LSU Ag Center’s website can be accessed at with lots of user-friendly information, including this article.

3/15/2019 6:12:52 PM
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