Tuesday, July 20, 2010

Brown Spots in the Lawn by Mary Small

Does your lawn have a case of “those horrid brown spots”? You’re not alone.  Mine’s got them, too. When spring rains and cool temperatures are followed by hot dry weather, brown patches and spots just seem to appear out of nowhere.  One of the most common causes is an improperly adjusted sprinkler system.

Check to see how yours is functioning.  Manually turn on each zone and observe where the water is and isn’t going.  When my husband and I did this, we discovered that one sprinkler head was knocked out of alignment.  Instead of heading for the lawn, the water was making a direct hit on a nearby shrub.  Some water made it past the shrub, but quickly dropped to the ground.

In another location, the sprinkler head popped up part way and was only irrigating a small area.  In a third spot, we discovered a partially plugged head. No wonder we had brown spots!

If you run the sprinkler system and don’t see any obvious problems (other than those darned brown spots), try the “tuna can test”.  Place several straight-sided containers (like empty tuna cans) in the zone you want to check.  Run the system for 15 minutes, then measure the depth of water in all the containers and average them. Which cans hold less than average? Which hold more?  This shows you where there might be adjustment issues.

Site features can create irrigation problems.  Sprinkler water that hits a tree trunk or similar “obstruction” will cause a dry spot on the opposite side.  Hot, dry and windy exposures may need twice the water of shaded lawns.  Sloped areas often brown because applied water runs down slope before it can sink in. Try the “cycle and soak” treatment on slopes by splitting their irrigation times into two or three parts.
Different types of heads apply different amounts of water. Mix head types in the same zone and you can easily apply too much and too little water at the same time! Low daytime water pressure often creates brown areas.  Apply water at night or in the wee hours of the morning to take advantage of higher water pressure and better irrigation coverage. 

For more information, see the following CSU Extension fact sheets: 
Operating and Maintaining a Home Irrigation System

Irrigation:  Inspecting and Correcting Turf Irrigation System Problems