Annual bluegrass is a very problematic weed in Oregon home lawns and landscapes.  This winter annual has the perfect life cycle for the climatic conditions in the Pacific Northwest, particularly the conditions west of the Cascade Mountains.  Annual bluegrass germinates in the fall when soil temperatures begin to drop.  The newly established plant thrives through the cool, wet winter while your lawn grows very slowly.  The weed then produces abundant amounts of seed through the spring before dying in the early summer as thing heat up.  The spring produced seeds ensure the survival of the next fall generation.  Therefore, pre-emergence herbicides applied in the fall are an essential tool when managing this problematic weed.  However, annual bluegrass also has a tendency to develop perennial biotypes when established in areas that receive frequent mowing, fertilization and irrigation, just like a well maintained home lawn.  Perennial biotypes (because they do not die annually) will not be affected by pre-emergence herbicides and in this case post-emergence products must be utilized.  However, postemergence herbicides capable of provide annual bluegrass control, with the exception of bispyribac sodium (Velocity) and ethofumesate (Prograss), will also kill the cool-season grasses grown in Oregon home lawns.  When considering using Velocity or Prograss it is important to note that this product will injury your lawn and multiple applications are required to achieve varied levels of control. 

Preemergence herbicides will prevent annual bluegrass germination if applied at the correct time; however, these herbicides will not control established weed.   Apply preemergence herbicides in early fall as soil temperatures approach 70° F (or an air temperature of 75° F) and again in the winter.  If you plan to seed your lawn, preemergence herbicides will prevent your seed from germinating.  Application of preemergence herbicides will have to been done every year, annual bluegrass is a master of survival and dormant seeds will popup if preemergence control is not executed annually.  Some preemergence herbicides affective on annual bluegrass include… 

• Common name : active ingredient 
• Pendulum : pendimethalin    
• Prograss : ethofumesate
• Balan: benefin
• Bensumec: bensulide
• Dimension: dithiopyr
• Quali-Pro Prodiamine:  prodiamine

It is not uncommon for home owners to spot treat lawns with non-selective herbicides like glyphosate (Round-Up) and then re-sod or seed these areas.  This is often the preferred method for control of perennial biotypes (annual bluegrass plants that live through the summer).  Applications of nonselective herbicides will kill your lawn and should be limited to spot treatment in problematic annual bluegrass areas, remember reestablishment form seed or sod is required.  Another possibility is establishing your lawn with glyphosate resistant ryegrass (Gly-Rye varieties include ‘Replay’ and ‘JS501’).  A lawn established with this grass can tolerate applications of glyphosate (Round-Up) applied at 0.25 lbs of active ingredient per acre (8-12 fl oz of product depending on the formulation).  More information about Gly-Rye is available at… http://pesticidetruths.com/wp-content/uploads/2011/12/Reference-Jacklin-Newsletter-2011-Vol.-14-Issue-2-Glyphosate-Tolerant-Perennial-Rye.pdf

Annaul bluegrass is a diverse and highly adaptable plant; therefore, repeated use of one herbicide can result in resistant populations.  To prevent this from occurring cycle though the different preemergence products and spot treat with nonselective products as needed.    

To prevent annual bluegrass invasion raise your mowing height (to 3 inches if possible).  High mowing heights will encourage turf competition and reduce annual bluegrass germination.  Fall nitrogen fertilizer applications should be kept to a minimum.  A balanced fertility program 6 lbs of nitrogen, 1 lbs of phosphorus and 4 lbs of potassium, supplemented with 2 lbs of sulfur annually will enhance turf growth and development while minimizing annual bluegrass establishment.  If you plan to aerify (core cultivate) your lawn this process should be done in the spring during active turf growth, fall aerification often promotes annual bluegrass establishment.

Finally, I would like to remind you that annual bluegrass is perfectly adapted to life in the Pacific Northwest; therefore, preemergence herbicide applications will need to be made in the fall and winter annually, and occasional spot treatments will nonselective herbicides will be required for the management of this highly invasive weed.