Fall is Time to Fertilize Cool-Season Grasses

A turf grass will fall into one of two categories: warm-season grasses or cool-season grasses. These different types of grasses are fertilized at different times of the year.

The cool-season grasses - fescue, Kentucky bluegrass, etc. - are fertilized in the fall. The term for this is winterizing your lawn. This is when they get the majority of their fertilizer. They receive more fertilizer in the spring. Cool-season grasses need no fertilizer in the summer, since they are slowing down their growth to survive the heat. Most of the turf grown in our area is warm- season grass.

With warm-season turf grass, you fertilize in spring and summer. That is the time of the year when these grasses are growing.

As fall and winter nears and the days get shorter, warm-season grasses slow down and start to harden off for winter. They are not using up the nutrients like they were in the spring and summer, so the majority of fertilizer that you put out in the fall is not taken up by the grass.

In addition, nitrogen fertilizer causes the grass to continue to grow, keeping the plants tender and more susceptible to cold damage.

One nutrient that you can fertilize with in the fall is potassium. Potassium is the last number that you find on the fertilizer bag. Potassium strengthens plants' cells and cell walls. It is very important in increasing winter hardiness, and it boosts drought and disease resistance.

You can buy fertilizers that only have potassium in them. One of these is muriate of potash. The level of potassium in your soil will determine if you need to apply the fertilizer in the fall. A soil sample is the best way to determine it. If the soil sample shows a high level, you don't need to apply the fertilizer.

The major problem that we see with fall fertilization of turf grass is diseases. There are two diseases that become major problems in the fall - large patch and take-all disease. Both of these diseases like wet conditions, cool temperatures and an increase in nitrogen. They will attack both cool-season and warm- season grasses.

Large patch is caused by the fungus Rhizoctonia. There are several species of this fungus that attack turf grass. In the past, this disease was known as brown patch, but a few years ago plant pathologists changed how we label this disease. If the disease is in cool-season grasses it is called brown patch. If it is found in warm-season grass it is called large patch. This disease is circular in shape. It starts out as a small circle and continues to spread out from the starting point. There could be several of these circles in a yard, and they could grow together to cover a whole yard.

To help identify if it is large patch, you need to look at the border where the healthy grass meets the diseased grass. Early in the morning while the grass is wet, you can see a smoky, grey color on the grass. As the grass dries, this color will go away. This is the reproductive part of the fungus. To treat for large patch, you need to apply a fungicide and change your management practices. Any of the fungicides for lawns work on large patch. You can help control the disease by letting the grass dry out and not applying any nitrogen fertilizer.

Take-all disease started showing up in our area about two years ago. This is a disease that attacks the grass about the time that we get our first frost. You don't see the symptoms of the disease until the grass doesn't green up next spring.

This disease, caused by the fungus Gaeumannomyces graminis, likes late applications of nitrogen and wet conditions. Also, this disease likes soils with a high pH level, above 6.5. Therefore, apply lime only when called for on a soil sample.

To control this disease, you have to improve the drainage in the soil, use ammonium-based fertilizers during the growing season, use manganese sulfate at 2 pounds per 1,000 square feet and apply a fungicide during the last week of September to the first week of October. Homeowners can use Bayleton, triadimefon, to help control this disease. The timing of the application is important.

With our warm-season turf grass, fertilizing at the right times can help reduce a number of problems.

Columbia County Extension Agent Charles Phillips can be reached at (706) 868-3413 or by e-mail at charlesp@uga.edu. The extension Web address is www.ugaextension.com/columbia.

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