Are You Seeing Circles?

If you are like me, you may have spent countless hours watching the Olympic coverage the past few weeks, but I am not talking about those circles.  Lawns in the Central Valley have been taking a beating with the 15 plus days of temperatures exceeding 100 degrees. We have seen spots and circles as a result of the weather conditions favoring various disease and insect activity.

Before one jumps to the conclusion that they must have either a disease or insect problem because they see parts of their lawn turning brown, one must first see if the lawn has sufficient water in the top 4-6 inches to meet the lawn’s water needs.  If a screwdriver can be pushed into the ground 4-6 inches with moderate effort most likely there is sufficient water in the root zone.  Dry soils will only allow the screwdriver to go in 2 inches or less in non-sandy soils.

Next, one looks for patterns to the brown areas.  Are they circular spots or rings or angular?  Do the leaves have spots or lesions or are they chewed off shorter than the mower could possibly cut (possible cutworms or webworms)?

Lawn diseases are typically circular in their pattern.  Three distinct fungal pests thrive in the summer heat on tall fescue, rye, and bluegrass lawns.  Pythium is a water mold that can quickly cause small to large brown blotches in the lawn and is associated here with excessive watering in most cases.  It is not the number one problem, but it is relatively easy to reduce its damage by reducing the amount of water applied and not mowing the lawn when it is wet and or boggy.  Rhizoctonia brown patch will form small to large patches of browning turf due to the numerous tan lesions that damage the blades.  It thrives in sunny locations with poor air movement and often increases with evening watering.  Faint to distinct yellow-brown circles with green centers in the lawn ranging from 1 to 12 feet in diameter usually signals southern blight.  One can usually note little seed-like sclerotia along the outside edge in the thatch to confirm the identification. By mid September these will likely all be subsiding as the evenings start to cool off.

Cultural practices like watering deeply 3-4 times a week and avoiding irrigation in the evening may reduce disease incidence.  Preventive fungicides are available that provide up to 30 days control and are a great option for the months of June, July, and August.  Like people, the cool-season grasses enjoy the 65-80 degree weather and cool nights, but unfortunately we have no control on that.  

Relief is coming soon!