Problems with Poa

Poa annua

Perhaps you have seen this invasive “winter grass” invade your lawn and flower beds at home in past years. It is a clumpy, spring-green tuft of grass that first appears in October, continues to grow denser and put out an abundance of seed mid to late winter, and finally disappears as the weather warms up in May and June.  Annual bluegrass, Poa annua, is native to Europe, but now found world-wide.  It can grow 6-8 inches tall and can tolerate mowing heights below 1/8 inch as seen on golf course putting greens.  It has been estimated that Poa can produce as many as 14,000 to 63,000 viable seeds per square foot in a year on a golf course green!  Seeds can remain dormant for a few years, but with regular irrigation, most do not show much of a dormancy period.

So, why is Poa a problem, it is green after all. The biggest problem with Poa annua in the Central Valley is that it is a true annual that will abandon you by early summer in full sun areas because it cannot tolerate the heat.  Germination will start as early as August when soil temperatures start to drop below 70 degrees.  Germination will continue throughout the winter and by December (or before) you will start to see the appearance of the open-panicle seedheads popping up.  By February and March you will see the yellow-green patches with seedheads across the lawn areas and throughout the flower beds.  Two to three months later most of the plants will only be brown tufts scattered about.  Just think about the poor golf course superintendent that has to manage greens that are mowed daily at extremely short heights, excessive summer heat, and golfers trampling over the turf throughout the day.  His job is to keep alive what Poa he has and try to minimize its further spread.

Poa annua flowerhead

So what can be done?  If possible, one should try to limit the spread of Poa by not moving the seeds with mowers from bad turf to good turf.  Mowing when the grass is dry can help somewhat, but certainly washing off the mower between lawns is obvious during periods of seeding.  Secondly, a pre emergent herbicide should be applied mid to late August to reduce the likelihood of seed germination.  One must also consider if the lawn is going to be overseeded or spot-seeded late September or early October.  The pre emergent will possibly cause a poor or weak stand of new seedlings as the herbicide will reduce root development.  There are a few options for selectively controlling Poa annua in existing lawns, but they are not available to homeowners and generally they are specific for either warm or cool season grasses. 

Controlling Poa annua in lawns can be tricky, but it’s a no-brainer to apply a pre emergent now in flower beds to interrupt the life cycle this winter and save you a lot of work pulling weeds this spring.

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Why is My Lawn Brown?

This is not an easy question to answer without first asking a few background questions. If the spots are irregular in shape, and not round, I would start with the sprinkler system.  Do you have automatic sprinklers, manually operated sprinklers, or none of the above?  How often do you water? When do you water?  How long do you water?  Next I would look at the sprinklers while they are running.  Are they operating properly?  Is the spacing allowing head to head coverage?  Are there any shrubs or trees blocking the pattern?  Are the heads level and adjusted to the right height? 

Dry spot from lack of water

A soil probe can take a core sample of the top 4-6 inches and tell you if the soil has adequate water and how deep down the water has traveled.  Ideally, you would see good moisture down 4-6 inches deep.  If you can’t get the probe down below 2-4 inches, the soil is likely water deficient.  A standard 6-8 inch screwdriver can also be an easy tool to probe how far down the soil is moist.  Generally, you should be able to push the screwdriver down 4-6 inches with moderate effort.  Too easy…too wet; too hard…too dry.

Pythium Disease

Brown lawns could also be the result of numerous pests.  Diseases generally cause circular yellow-brown patterns in the lawn and symptoms vary with the pathogen involved.  Insect damage can be somewhat random in appearance.  Some pest attack the roots causing failure of the lawn in patches while others feed on the leaves causing thinning or yellowing.

Lastly, and you may not want to hear this, but there could be several cultural habits that cause a lawn to fail during stress periods.  Over watering or watering frequently, especially in the evenings, could encourage disease activity.  Over fertilizing, especially spilling fertilizer, can cause rapid browning due to the high salt content (like pet urine burns).  Mowing too short, too infrequently, or with dull mower blades can stress the lawn as well.  Ideally they should be mowed at least weekly and at the proper height for that particular grass type.  There are also the odd things like sunlight reflection off a large picture window, placing car floor mats on the lawn while cleaning the car, construction cleanups, and space aliens landing at night. 

Hopefully, you now have some ideas on how to troubleshoot your brown spots, or you can always give us a call for a free analysis.  The weather is going to become cooler shortly and many of this summer’s brown spots will be disappearing for several months. Hooray!