GARDENING: Short duration waterings encourage turfgrass diseases

We still are receiving many calls concerning turfgrass diseases this year. Some of these are real diseases and others are management problems. I would strongly urge anyone with a lawn not to apply water to their lawns in short waterings, particularly at night, unless they need to prevent runoff into the streets.

First of all, short duration watering encourages turfgrass diseases. Turfgrass diseases will run rampant whenever stressed, warm turfgrass is kept wet. This is a plain, simple truth for any plant.

Secondly, most turfgrass diseases favor wet conditions. Frequent short waterings at night keep the turfgrass environment wet and never give it a chance to dry out. This is very favorable for disease development. Diseases like warm, humid places to grow. Your turfgrass lawn is like a pygmy jungle. The air above the grass where weather instruments are located may be dry, but the air inside that pygmy jungle is as humid as any tropical rain forest after a rain.

Thirdly, short irrigation cycles waste water. As any farmer knows, when water is applied in short cycles there is more water lost from evaporation.

What is the answer then? We must go back to the old fashioned basics of watering your lawn. Water the lawn long enough to water the entire root zone. On some lawns this may be to a depth of 12 inches. On others this may be only 2- or 3-inch depths. The only way to know is to stick a long screwdriver in the lawn in several places and see how far it can penetrate. The roots can go this deep as well if the lawn is managed properly.

Timing may vary from 10 or 12 minutes for spray heads to double that for sprinklers that rotate. Try to do the entire irrigation in one application if you can. If you do get runoff or puddling, then split it into two or three applications in succession, no more than half an hour apart.

Water during the early morning hours. Avoid nighttime applications. If the disease seems to be spreading slowly or hardly at all, then avoid applying a fungicide. It is my recommendation that if you are relatively certain that you have a disease problem on your lawn and it appears to be actively spreading, then make an application of a broad-spectrum fungicide to contain the disease. Do this according to the label only.

Remember that these products are poisons and have associated health risks. Some of the health risks are noted on the bag or label with the words "Caution," "Warning" and "Danger." Read the label to learn of some of these associated health risks.

If at all possible avoid the application of pesticides unless it is warranted. If the disease problem is not spreading rapidly, try changing some of your management practices instead of applying a fungicide. Increase or decrease your mowing height, irrigate at a different time or cut back on fertilizers.

Other possible causes of brown spots? One reason for brown spots is irrigation. In the spring we often get caught off guard when hot, dry weather is upon us. This year in particular hot weather was delayed and then came on very quickly with dry winds.

Brown spots caused by a lack of water can be distinguished from other types of brown spots usually because the leaf tips dieback in the affected area. If it's severe, the tips or blades may dieback all the way to the soil. However, when the brown leaf blades are peeled back exposing the inner stem, the stem is succulent and healthy. When plenty of water and fertilizer is resupplied, the healthy stems will explode with new leaves in one or two weeks.

Overseeding of Bermuda grass for winter color should start in about a month, and the window for getting it done will be about three to four weeks. Use perennial rye grass at a rate of 8 to 10 pounds per thousand square feet for the homeowner. Professionals can use lighter rates if they are experienced. If you are planning to keep it mowed short, then you should double the seeding rate.

The ideal time to overseed is when the temperatures have been cooling off so the Bermuda grass growth is slowing but rye grass still loves it. The temperatures should begin to discourage Bermuda grass growth and encourage rye grass growth. This will help rye dominate the grass stand. Because rye grass is a cool-season grass, then this should be when daytime temperatures are in the 80s and nighttime temperatures are in the 50s or high 60s. As the fall temperatures continue to drop, Bermuda grass will continue to slow in growth and rye will dominate the seeded area.

What happens if you overseed too early? The stand of winter rye grass will be spotty. In the hottest places the Bermuda won't allow the rye to take because it will dominate with its competitive advantage because of the temperatures. The rye grass will be successful only where it is cooler, such as shady areas or north sides of buildings, or wetter areas such as in low spots. So if you are timing your overseeding to the golf course operation, be careful. They may be too early this year because they are forced to be early, not because the timing is right.

Question: There are dead spots in my lawn from either disease or insects that are quite large. How do I fix these?

Answer: If this is a tall fescue lawn then you must wait until it gets cooler, probably around the end of September. If this is a Bermuda lawn then you must repair it immediately or it won't recover by fall. In late September, the fescue lawn should be mowed close but not closer than 1 1/2 inch.

Check the irrigation system and make sure that you have even coverage. The areas that are dead should be raked until you can see bare ground. If these are large areas, you might consider renting a dethatcher or power rake to remove the dead grass.

The seed can be sown directly into the dead areas. The lawn does not need to be cultivated. Select a superior tall fescue for home lawns, not Kentucky 31. These are usually quite a bit more expensive than K 31. Actually, K 31 has many good qualities but most people are not happy with its coarse appearance.

Fertilize the dead, raked areas with a lawn starter fertilizer high in phosphorus, the middle number on the bag. Probably the least expensive fertilizer available to do this is 16-20-0. Spread the seed and fertilizer evenly in the raked areas.

Cover with a topdressing making sure that it is no deeper than 1/4 inch. This can be manure if you don't mind the inconvenience of the smell and messiness. Otherwise, any kind of soil that is finely textured like a potting soil will work. Water the area three times a day for five minutes until the seed germinates. Usually in four to five days.

Bob Morris is a horticulture specialist with the University of Nevada Cooperative Extension.


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