Lawn Diseases Struggle When the Humidity is Higher than Normal

Q. I live in Henderson where we enjoy having a lawn as part of our yard. It was thick and beautiful when we moved in, but it soon withered after we made some changes to sprinkler layouts and had the water off for awhile. I laid fresh sod and it too struggled. I tried a fungicide and that seemed to help but it then died completely.  Now the rest of the lawn is headed in the same direction. I’m at the point of desperation and could use some sound advice in the midst of some differing opinions.

This is the lawn the reader talked about. It is dying in patches. The reader asked me to look at it (consult) but I think the disease problems we had (high humidity) earlier had a lot to do with it.

A. Outside of watering, some lawns experienced disease problems earlier in the season that lingered after we had high humidity due to the rain. That change in our weather encouraged plant diseases to occur. In the desert, it’s usually the higher humidity that’s the problem.

I will take a look at this lawn and see if the disease is advancing or has stayed put. That will tell me what his options are. Now he must stop the lawn disease (if advancing) and get the grass to come back.

The humidity is now below 15% (except directly above lawns) and lawns should not need a fungicide application to keep the disease from spreading if we allow the lawn to dry after we apply water, and it is in good health. When there was higher humidity, some lawns along with some other plants, may have needed a fungicide. A lot of it had to do with the lawns current health.

If you applied a lawn fungicide, it should have stopped needing the applications if the general humidity was above let’s say 25%. Plant disease susceptibility is sometimes compared to a three-legged stool. Plants are susceptible to fungal disease if: 1. the disease organism is present, 2. general health and susceptibility of the plant is good, and 3. the current weather. In this case, all diseases like moisture. A couple of months ago the weather (humidity) was the problem. The higher humidity is now over. The relative humidity is now in the “desert” range. I think you are seeing old lawn disease damage (unless the lawn grasses are in poor health).

Make sure you follow label directions when you apply any fungicide. Any traditional broad-spectrum fungicide should work, but generally the higher-priced fungicides for lawns are usually a better choice in that respect.

This fall we should be watering lawns about two to three times each week. No more than four times each week for sure! Water early in the morning (imperative) and wet the lawns from 8 to 10 inches deep in a single application when you water. Sloped areas, or hard soils, may need multiple starts, about 30 minutes to one hour apart, to keep the water from “puddling” into low spots.

            Your lawn may not need it but try “aerifying” your lawn with a gasoline driven core aerifier. Then “topdress” your lawn with a rich compost to fill the aerification holes. Irrigate your lawn immediately after this. This process of filling the aerification holes, followed by topdressing and irrigation, improves the rooting depth of the grass. This will improve a lawns (grass) health.